LECTURE 2
DERMATOZOONOSIS. PYODERMA.
SCABIES
Scabies is an itchy, highly contagious skin condition caused by an infestation by the itch mite Sarcoptes scabiei.
Direct skin-to-skin contact is the mode of transmission.
A severe and relentless itch is the predominant symptom of scabies.
Sexual contact is the most common form of transmission among sexually active young people, and scabies has been considered by many to be a sexually transmitted disease (STD).
Scabies produces a skin rash composed of small red bumps and blisters and affects specific areas of the body.
Treatment includes oral or topical scabicidal drugs.
What is scabies? What causes scabies infestation?
Scabies is an itchy, highly contagious skin disease caused by an infestation by the itch mite Sarcoptes scabiei. Mites are small eight-legged parasites (in contrast to insects, which have six legs). They are tiny, just 1/3 millimeter long, and burrow into the skin to produce intense itching, which tends to be worse at night. The mites that infest humans are female and are 0.3 mm-0.4 mm long; the males are about half this size. Scabies mites can be seen with a magnifying glass or microscope. The scabies mites crawl but are unable to fly or jump. They are immobile at temperatures below 20 C, although they may survive for prolonged periods at these temperatures.
Scabies infestation occurs worldwide and is very common. It has been estimated that worldwide, about 300 million cases occur each year. Human scabies has been reported for over 2,500 years. Scabies has been reported to occur in epidemics iursing homes, hospitals, long-term care facilities, and other institutions. In the U.S., it is seen frequently in the homeless population but occurs episodically in other populations of all socioeconomic groups as well.
How do you get scabies?
Direct skin-to-skin contact is the mode of transmission. Scabies mites are very sensitive to their environment. They can only live off of a host body for 24-36 hours under most conditions. Transmission of the mites involves close person-to-person contact of the skin-to-skin variety. It is hard, if not impossible, to catch scabies by shaking hands, hanging your coat next to someone who has it, or even sharing bedclothes that had mites in them the night before. Sexual physical contact, however, can transmit the disease. In fact, sexual contact is the most common form of transmission among sexually active young people, and scabies has been considered by many to be a sexually transmitted disease (STD). However, other forms of physical contact, such as mothers hugging their children, are sufficient to spread the mites. Over time, close friends and relatives can contract it this way, too. School settings typically do not provide the level of prolonged personal contact necessary for transmission of the mites.
Can you catch scabies from a dog or cat?
Dogs and cats are infected by different types of mites than those which infect humans. Animals are not a source of spread of human scabies. Scabies on dogs is called mange. When canine or feline mites land on human skin, they fail to thrive and produce only a mild itch that goes away on its own. This is unlike human scabies which gets worse and worse unless the condition is treated.
What are risk factors for scabies?
Scabies can infest any human who comes in contact with the mites. The only known risk factor is direct skin contact with someone who is infested. The contact one experiences in social or school settings is not likely to be sufficient to transmit the mites. Sexual or other close contact (such as hugging) is required to spread the condition. The condition does appear in clusters, so outbreaks may occur within a given community.
What does scabies rash look like? What are scabies symptoms and signs?
Scabies produces a skin rash composed of small red bumps and blisters and affects specific areas of the body. Scabies may involve the webs between the fingers, the wrists and the backs of the elbows, the knees, around the waist and umbilicus, the axillary folds, the areas around the nipples, the sides and backs of the feet, the genital area, and the buttocks. The bumps (medically termed papules) may contain blood crusts. It is helpful to know that not every bump is a bug. In most cases of scabies affecting otherwise healthy adults, there are no more than 10-15 live mites even if there are hundreds of bumps and pimples on the skin.
The scabies rash is often apparent on the head, face, neck, palms, and soles of the feet in infants and very young children but usually not in adults and older children.
Textbook descriptions of scabies always mention “burrows” or “tunnels.” These are tiny threadlike projections, ranging from 2 mm-15 mm long, which appear as thin gray, brown, or red lines in affected areas. The burrows can be very difficult to see. Often mistaken for burrows are linear scratch marks that are large and dramatic and appear in people with any itchy skin condition. Scratching actually destroys burrows.
What does scabies feel like?
It is important to note that symptoms may not appear for up to two months after being infested with the scabies mite. Even though symptoms do not occur, the infested person is still able to spread scabies during this time. When symptoms develop, itching is the most common symptom of scabies. The itch of scabies is insidious and relentless and often worsens over a period of weeks. The itch is typically worse at night. For the first weeks, the itch is subtle. It then gradually becomes more intense until, after a month or two, sleep becomes almost impossible.
What makes the itch of scabies distinctive is its relentless quality, at least after several weeks. Other itchy skin conditions — eczema, hives, and so forth — tend to produce symptoms that wax and wane. These types of itch may keep people from falling asleep at night for a little while, but they rarely prevent sleep or awaken the sufferer in the middle of the night.
How is a scabies infestation diagnosed?
Scabies is suggested by the presence of the typical rash and symptoms of unrelenting and worsening itch, particularly at night. Ultimately, the definitive diagnosis is made when evidence of mites is found from a skin scraping test. By scraping the skin (covered with a drop of mineral oil) sideways with a scalpel blade over an area of a burrow and examining the scrapings microscopically, it is possible to identify mites, eggs, or pellets. This process can be difficult, however, since burrows can be hard to identify. Sometimes scratch marks are mistaken for burrows, and even the examination of scrapings from 15 or more burrows may only reveal one or two mites or eggs. If the characteristic physical findings are present, scabies can often be treated without performing the skin scrapings necessary to identify the mites.
What are treatment options and home remedies for a scabies infestation?
Curing scabies is rather easy with the administration of prescription scabicide drugs. There are no approved over-the-counter preparations that have been proved to be effective in eliminating scabies.
The following steps should be included in the treatment of scabies:
1. Apply a mite-killer like permethrin (Elimite). These creams are applied from the neck down, left on overnight, then washed off. This application is usually repeated in seven days. Permethrin is approved for use in people 2 months of age and older.
2. An alternative treatment is 1 ounce of a 1% lotion or 30 grams of cream of lindane, applied from the neck down and washed off after approximately eight hours. Since lindane can cause seizures when it is absorbed through the skin, it should not be used if skin is significantly irritated or wet, such as with extensive skin disease, rash, or after a bath. As an additional precaution, lindane should not be used in pregnant or nursing women, the elderly, people with skin sores at the site of the application, children younger than 2 years of age, or people who weigh less than 110 pounds. Lindane is not a first-line treatment and is only recommended if patients cannot tolerate other therapies or if other therapies have not been effective.
3. Ivermectin, an oral medication, is an antiparasitic medication that has also been shown to be an effective scabicide, although it is not FDA-approved for this use. The CDC recommends taking this drug at a dosage of 200 micrograms per kilogram body weight as a single dose, followed by a repeat dose two weeks later. Although taking a drug by mouth is more convenient than application of the cream, ivermectin has a greater risk of toxic side effects than permethrin and has not been shown to be superior to permethrin in eradicating scabies. It is typically used only when topical medications have failed or when the patient cannot tolerate them.
4. Crotamiton lotion 10% and cream 10% (Eurax, Crotan) is another drug that has been approved for the treatment of scabies in adults, but it is not approved for use in children. However, treatment failures have been documented with the use of crotamiton.
5. Sulfur in petrolatum applied as a cream or ointment is one of the earliest known treatments for scabies. It has not been approved by the FDA for this use, and sulfur should only be used when permethrin, lindane, or ivermectin cannot be tolerated. However, sulfur is safe for use in pregnant women and infants.
6. Antihistamines, such as diphenhydramine (Benadryl), can be useful in helping provide relief from itching. Sometimes, a short course of topical or oral steroids is prescribed to help control the itching.
7. Wash linens and bedclothes in hot water. Because mites don’t live long away from the body, it is not necessary to dry-clean the whole wardrobe, spray furniture and rugs, and so forth.
8. Treat sexual contacts or relevant family members (who either have either symptoms or have the kind of relationship that makes transmission likely).
Just as the itch of scabies takes a while to reach a crescendo, it takes a few days to subside after treatment. After a week or two, relief is dramatic. If that doesn’t happen, the diagnosis of scabies must be questioned.
Are cases of scabies often misdiagnosed?
Scabies is very easy to misdiagnose because early subtle infestation may look like small pimples or mosquito bites. Those affected may believe they have another condition, such as bedbug bites or other kinds of rashes. Over a few weeks, however, mistakes like this become evident as patients feel worse and worse with symptoms they can’t ignore.
What are possible complications of scabies?
The intense itching of scabies leads to prolonged and often intense scratching of the skin. When the skin is broken or injured due to scratching, secondary bacterial infections of the skin can develop from bacteria normally present on the skin, such as Staphylococcus aureus or beta-hemolytic streptococci.
Can a scabies infestation be prevented?
Scabies can be prevented by avoiding close personal contact with infested people. Sexual contacts and household members of people who develop scabies can be treated as soon as the condition is identified so that they will not develop the signs or symptoms of the condition. The treatment for these exposed people is the same as the treatment of the infested individual.
In what special situations can scabies be more easily spread?
Elderly and weakened people iursing homes and similar institutional settings may harbor scabies without showing significant itching or visible signs. In such cases, there can be widespread epidemics among patients and health care workers. Such cases are dramatic but, fortunately, uncommon.
What is Norwegian or crusted scabies?
Norwegian scabies, or crusted scabies, is a severe form of scabies first described in Norway. Crusted scabies almost always affects people with a compromised immune system and is observed most frequently in the elderly, those who are mentally or physically disabled, and in patients with AIDS, lymphoma, or other conditions that decrease the effectiveness of the immune response. Due to the poor function of the immune system, an individual may become infested with hundreds of thousands of the mites. The lesions of this distinctive form of scabies are extensive and may spread all over the body. The elbows, knees, palms, scalp, and soles of the feet are most commonly the original sites of involvement, and the scaly areas eventually take on a wart-like appearance. The fingernails can be thickened and discolored. Interestingly, itching may be minimal or absent in this form of scabies.
A particular danger of crusted scabies is that these lesions often predispose to the development of secondary infections, as with staphylococcus or streptococcus bacteria.
What is the prognosis (outlook) for scabies?
Scabies is curable with scabicide medications. Treatment failures are not common but are possible, and people with Norwegian scabies may require a combination of different treatment methods.
PEDICULOSIS
HISTORY
Head lice (pediculosis capitus) are small parasitic insects that live on the scalp and neck hairs of their human hosts. The presence of lice is most often detected through the presence of adult lice or nits (eggs) attached to the hair shaft of the host, most often at the nape of the neck and behind the ears. Complications of infestations are rare and involve secondary bacterial skin infection (Lebwohl, Clark & Levitt, 2007).
Pruritis (itching) is the most common symptom of a lice infestation, along with the following additional symptoms:
ü a tickling feeling or a sensation of something moving in the hair;
ü irritability and sleeplessness; and
ü sores on the head caused by scratching. Sores caused by scratching can sometimes become infected with bacteria normally found on a person’s skin (CDC, 2010).
DESCRIPTION OF ISSUE
Some people consider pediculosis to be a public health issue that is brought into the school setting. Families and school staff expend innumerable hours and resources attempting to eradicate lice infestations, both live lice and their nits. The Centers for Disease Control and Prevention (CDC) (2010) reports an estimated 6 million to 12 million infestations (some experts believe that the true prevalence is considerably lower) (Pollack, 2010) occur each year in the United States among children 3 to 11 years of age. It is thought that head lice infestations are often misdiagnosed when medical and lay individuals identify the presence of lice based on the presence of eggs (Pollack, Kiszewski & Spielman, 2000). In addition, millions of dollars are spent annually on pediculicides, lice combs, physician visits, and parental time away from work. In an effort to find an easy, effective, and safe treatment, a variety of alternative therapies (e.g., occlusive agents such as oil-based and grease-based products, electric combs, herbal shampoos and enzyme solutions,) have been attempted by parents. There is little scientific evidence regarding the effectiveness of these alternative treatments, and all have an associated cost (Frankowski & Bocchini, 2010). Treatment recommendations for pediculosis should be based on evidence based literature from public health, medical and nursing content experts rather than anecdotal reports or commercial advertisements.
Parents, school staff, and the community often become unduly anxious when a case of head lice occurs within a classroom, and this anxiety is multiplied if more than one case is identified. A negative social stigma frequently accompanies the identification of pediculosis as well as the frustration involved with the cost, time and effort needed for treatment and environmental control (Gordon, 2007). It is important, as a part of a comprehensive educational program, that the school nurse emphasizes that head lice are not associated with poor hygiene (Lebwohl, Clark & Levitt, 2007).
In 2007, international guidelines established for effective control of head lice infestations reinforced that policies that required a student to be free of nits to attend school, known as “no nit” policies, were based on misinformation rather than objective science and were therefore unjust and should be discontinued (Mumcuoglu et. al., 2007).
The CDC (2010) cites the following reasons to discontinue “no nit” policies in school:
ü Many nits are more than ¼ inch from the scalp. Such nits are usually not viable and unlikely to hatch to become crawling lice, or may in fact be empty shells, also known as casings.
ü Nits are cemented to hair shafts and unlikely to be transferred successfully to other people.
ü The burden of unnecessary absenteeism to the students, families and communities far outweighs the risks associated with head lice.
ü Misdiagnosis of nits is very common during nit checks conducted by nonmedical personnel.
RATIONALE
The school nurse is the key health professional to provide education and anticipatory guidance to the school community regarding best practice guidance in the management of pediculosis. The school nurse’s goals are to facilitate an accurate assessment of the problem, contain infestation, provide appropriate health information for treatment and prevention, prevent overexposure to potentially hazardous chemicals, and minimize school absence.
There is discussion in the scientific community on the best way to control head lice infestation in school children. No pediculicide is 100% ovicidal, and resistance has been reported with lindane, pyrethrins, and permethrin (Frankowski & Bocchini, 2010). New categories of pediculicides have recently been developed, including benzyl alcohol (CDC, 2010).
Head lice screening programs have not had a significant effect on the incidence of head lice in the school setting over time and have not proven to be cost effective (Frankowski & Bocchini, 2010). Research data does not support immediate exclusion upon the identification of the presence of live lice or nits as an effective means of controlling pediculosis transmission. By the time a child with an active head lice infestation has been identified, he or she may have had the infestation for one month or more and, therefore, poses little additional risk of transmission to others (Frankowski & Boochini, 2010). The school nurse is in a position to take the lead in eliminating school exclusion policies and, instead, incorporate evidence-based practices that reduce the stigma associated with head lice, and work to increase classroom time with an emphasis on keeping students in school (Gordon, 2007).
DEMODOCOSIS
Background
Observation of the arachnid, Demodex folliculorum, has been reported since 1840. This hair follicle mite is the only metazoan organism commonly found in the pilosebaceous components of the eyelid of humans.
Pathophysiology
D. folliculorum (all stages) is found in small hair follicles and eyelash hair follicles. In all forms, immature and adult, it consumes epithelial cells, produces follicular distention and hyperplasia, and increases keratinization leading (in eyelashes) to cuffing, which consists of keratin and lipid moieties.
Demodex brevis (all stages) is present in the eyelash sebaceous glands, small hair sebaceous glands, and lobules of the meibomian glands. Adults and immature forms consume the gland cells in all of these loci and, when infestations are heavy, can affect the formation of the superficial lipid layer of the tear film coacervate. Demodectic mites produce histologically observable tissue and inflammatory changes, epithelial hyperplasia, and follicular plugging.
Follicular inflammation produces edema and results in easier epilation of the eyelashes. It also affects cilia construction, and lashes are observed to be more brittle in the presence of demodicosis. Madarosis (loss of lashes) is associated with abundant mites, the loss of eyelashes as a result of intercellular edema in the hair shaft, and loss of hair resiliency. Although epithelial hyperplasia associated with follicular plugging is often encountered, dermal changes seldom extend beyond the perifollicular epidermal area. Once believed to be mite excreta, this plugging is now known to be epithelial hyperplasia with interspersed layers of lipid. The formation of a collar of tissue around the base of the lashes is observed clinically. This occurs significantly more often in follicles infected with D folliculorum. The epithelial hyperplasia is hypothesized to be most likely a product of the abrasive action of the mite’s claws.
Accumulation of waste material of the follicle mite may occur in affected follicles or sebaceous glands. Electron micrographs of the mite surface and feces show bacterial, viral, and rickettsial elements. Specific reports have revealed that both species pierce epithelial cells and consume cytoplasm. Only D brevis has been observed with channels burrowed to the germinal epithelium in the sebaceous glands.
Demodex species-induced pathologic changes have been implicated in dry eye conditions. When follicular plugging involves the meibomian gland (D brevis) or the gland of Zeis (D folliculorum or D brevis), reduction of the superficial lipid layer of the tear film occurs. The effect of D brevis on the meibomian structure has been implicated in chalazion formation. D brevis has been observed in the center of these meibomian granulomas. Lid infestation by the Demodex species may or may not accompany dermatologic changes of the nose, the cheek, or the forehead.
D. folliculorum has been suggested as a factor in pityriasis folliculorum. This dermal inflammation manifests itself as a diffuse erythema of the affected areas; scaly, dry skin; and, in certain cases, rosacealike lesions.
Epidemiology
Mortality/Morbidity
Madarosis (loss of lashes) may result from untreated demodicosis.
Race
No racial predilection has been observed.
Sex
Infestation by these parasites is equal in males and females. Infestation is correlated to the number of sebaceous glands but not to the density of the hair follicles.
Age
Post reported that D folliculorum was observed in 84% of the sample population with a mean age of 61 years and in 100% of those older than 70 years.
History
Symptoms
ü Ocular irritation
ü Itching
ü Scaling of lids
Physical
ü Gross observation
o Lid thickening
o Scaling of lids
o Madarosis (loss of lashes)
o Conjunctival inflammation
o Meibomian gland dysfunction
o Rosacea
o Decreased vision
ü Slit lamp findings
· Collar of tissue around the base of the eyelashes
· Follicular distention
· Dry eye
· Cornea
· Superficial corneal vascularization
· Marginal corneal infiltration
· Phlyctenule-like lesion
· Superficial corneal opacity
· Nodular corneal scar
Causes
· Demodex species specific to humans occupy 2 periocular sites hidden from external observation. They are small in size and possess the ability to move across the skin surface.
· D folliculorum is found in hair and eyelash follicles associated with pilosebaceous glands in the eye or elsewhere on the face and the body. A single follicle may contain as many as 25 D folliculorum organisms.
· D brevis leads a much more solitary lifestyle in sebaceous glands of the body and in the meibomian gland and the gland of Zeis.
· D folliculorum measures 0.3-0.4 mm in length, whereas D brevis is one half the size of D folliculorum (0.15-0.2 mm) with similar structure of the head and the thorax but a shorter abdomen.
· The 8 legs of this arachnid are segmented and provide locomotion at a rate of 8-16 mm/h.
· D folliculorum and D brevis, also known as follicle mites, are believed to be more active in the dark, although capture in daylight is possible.
· The bright light of the day and especially the biomicroscope cause the mite to recede back into the follicle. Therefore, the mite can be observed only when an epilated lash is observed under a low-power microscope.
· The life stages of D folliculorum begin with copulation at the mouth of the follicle. Reproduction is believed to occur in darkness; a fact that is significant in symptomatology and treatment.
· Following copulation, the female burrows back into the follicle near the opening of the pilosebaceous gland and lays her eggs.
· Spickett reported the life cycle of D folliculorum and estimated that only 14.5 days elapse from ovum to adult stage, including 120 hours as an adult. Females may live an additional 5 days after oviposition.
· Sexes are separate; sexual maturity is reached in the larval form (neoteny).
· Females are territorial; they remain in their respective follicles and wait for the nomadic philandering males that travel over the surface of the skin from one follicle to another in seek of females.
· Adults reside in the follicle parallel to the hair shaft, head inward, often with the tail end (opisthosoma) protruding onto the surface of the skin at the base of the eyelash.
Differential Diagnoses
Laboratory Studies
ü Diagnosis is made on a high index of clinical suspicion.
ü Occasionally, nasal skin scrapings may be requested to rule out the possibility of acne rosacea.
Procedures
Slit lamp biomicroscopy
Histologic Findings
All reported histologic sections of lid follicles infested with D folliculorum show distention and thickening. Coston claims that less than half the specimens he observed showed perifollicular lymphocytic infiltration.[1] Follicular inflammation produces edema and results in easier epilation of the eyelashes. It also affects cilia construction, and the lashes are observed to be more brittle in the presence of demodicosis. Dermal changes seldom extend beyond the perifollicular epidermal area, although epithelial hyperplasia associated with follicular plugging is often encountered.
Medical Care
The treatment regimen is divided into in-office care and at-home care.
ü In the office, D folliculorum can be lured to the follicle surface with the use of volatile fluids, such as ether (not allowed in the United States), brushed vigorously across the external lid margin, following 0.5% proparacaine instillation. Five minutes later, a solution of 70% alcohol is applied in a similar manner. This regimen is reported to successfully reduce both the symptoms and the observed number of mites by the end of 3 weekly visits. Ether and alcohol should be used with caution, and corneal contact should be prevented.
ü A combination of this in-office treatment with a home regimen is suggested. The home regimen includes scrubbing the eyelids twice daily with baby shampoo diluted with water to yield a 50% dilution and applying an antibiotic ointment at night until resolution of symptoms.
ü Various treatments have been used to control Demodex mites. Most treatments involve spreading an ointment at the base of the eyelashes at night to trap mites as they emerge from their burrow and/or move from one follicle to another.
o Mercury oxide 1% ointment is frequently used.
o Pilocarpine gel reduced the number of mites and alleviated the symptom of itching in 11 patients in a nursing home. Celerio et al hypothesized that pilocarpine was directly toxic to the mites because its muscarinic action impedes respiration and motility.
ü The latest popular treatment regimen includes the use of 50% tea tree oil with Macadamia nut oil, applied with cotton tip applicators, after one drop of tetracaine.
o Aggressively debride the lashes and the lash roots first with scrubs. Try to get the oil into the lash roots and along the lashes to kill any eggs. Treat the eyebrows as well. Three applications, 10 minutes apart, per visit are recommended; treatment is completed with compounded 20% tea tree ointment. Repeat for 3 visits, each one week apart.
o Home regimen includes the following:
§ Use tea tree shampoo on hair and eye lashes every day.
§ Use tea tree soap or face wash every day.
§ Buy new makeup and discard old makeup; do not use makeup for 1 week.
§ Clean sheets and buy new pillows.
§ Check spouse; if both have this problem, both need to be treated.
§ Check pets.
§ For the first few weeks, use the ointment at night after tea tree shampoo scrubs. If inflammation is present, combination steroid-antibiotic ointments may be applied for one week. This is then replaced with a pure antibiotic ointment or with compounded 10% tea tree ointment.
ü Antibiotics
· Erythromycin ophthalmic (E-Mycin)
· Mercury oxide 1% ointment
· Cholinergics/miotic agents
· Pilocarpine 4% gel (Akarpine, Adsorbocarpine, Pilagan)
Further Outpatient Care
Eyelash scrubs twice daily with a 50-50 mixture of baby shampoo and water using a cotton swab or a rough washcloth provide symptomatic relief. The assumption that patients are knowledgeable about this procedure should not be made; demonstrating the eyelash scrub technique to the patient may be necessary.
The patient should be prescribed two 3.5-g tubes of a viscous ointment, preferably an antibiotic ointment, mercuric oxide ointment, or 10% tea tree oil ointment. The patient should be instructed to squeeze out 1 inch of ointment and apply liberally to each lid immediately before bedtime. This is believed to inhibit the reproductive attempts of the adult Demodex. The patient is also instructed to wash out the ointment every morning with the eyelash scrubs.
Preventive facial hygiene with daily soap and water washes is encouraged. Long-term compliance may be a problem in patients with dry skin.
Dermatologic consultation may be helpful in a patient with recurrent episodes or in those with accompanying dermatologic involvement.
Typically, 3-4 weeks of treatment is necessary. In patients who respond to the above outlined treatment, the eyelid scrubs may be reduced to once a day and an ointment at bedtime.
Consequently, the treatment is reduced until the condition resolves or recurs. If recurrence of symptoms occurs during the tapering period, the patient is advised to go back to the previous treatment level and to continue at that level.
If the patient is unresponsive to treatment, consider noncompliance or other underlying etiologies.
Inpatient & Outpatient Medications
50-50 mixture of baby shampoo and water
Erythromycin ointment
Mercury oxide 1% ointment
Pilocarpine 4% gel
10% tea tree oil ointment
PYODERMA
Although pyoderma is common, the clinical signs can be overlooked. The lesions consistent with pyoderma include papules, pustules, collarettes, and patchy alopecia.
Pyoderma Management:
Recognition of the type and depth of infection and, in many instances, identification of the pathogenic organism in order to make appropriate treatment recommendations. Treatment usually involves the use of systemic antibiotics, often accompanied by topical therapy.
Treatment choices vary depending on whether the pyoderma is a first-time infection or whether it is recurrent iature.
Treatment choices also depend on whether the infection is focal or generalized, surface, superficial or deep.
Factors to consider when choosing an antibiotic
Choice of antibiotics will depend on many factors:
These include the type of infection.
Depth of infection.
The cost of the antibiotic.
Route and frequency of administration.
Potential side effects of the drug need to be taken into account.
The impact that the antibiotic may have on the normal flora may also need to be considered.
Empirical antibiotic selection
Antibiotics may be chosen without prior culture and susceptibility in a number of situations. Specifically, antibiotics may be empirically chosen in uncomplicated superficial skin infections, in recurrent infections when the previous antibiotic choice successfully cleared the infection, and in deep infections pending culture and susceptibility results.
Because Staphylococcus pseudintermedius (formerly known as S. intermedius) is the most frequent organism isolated in canine skin infections, antibiotics chosen should have a known spectrum of activity against Staphylococcus spp. Antibiotics that should be avoided for empirical treatment of pyoderma include penicillin, ampicillin, amoxicillin, and tetracycline.
Antibiotic selection based on culture and susceptibility testing
Cultures should be obtained from all cases of deep pyoderma, skin infections that fail to respond to empirical treatment, infections in dogs on immunosuppressive medications, infections in dogs with prior exposure to many classes of antibiotics (eg. recurrent pyodermas), and lesions in which intracellular rod bacteria are identified cytologically.
Antibiotic choices
First-line antibiotics are those antibiotics that may be chosen empirically or based on culture and susceptibility that target Staphylococcus spp. primarily with minimal impact on other bacteria. Antibiotics included here are erythromycin, lincomycin, and clindamycin. These antibiotics have a narrow spectrum of action and are considered bacteriostatic for most bacteria. They are generally effective when chosen empirically to treat first-time skin infections; however, repeat exposure to these antibiotics results in the development of resistance. In addition, cross-resistance occurs among these three antibiotics. Therefore, use of these antibiotics to treat recurrent infections should be based on culture and susceptibility results.
Potentiated sulfonamide antibiotics (trimethoprim-sulfonamide; ormetoprim-sulfamethoxine) may also be considered as first-line antibiotic choices but their use should be avoided when long-term administration is required. Potentiated sulfonamides are bactericidal and demonstrate good efficacy against Gram-positive bacteria. Bacterial resistance to this class of antibiotics is quite variable, ranging from 0 to 33%; therefore, use of this antibiotic based on culture and susceptibility results may be more appropriate. Side effects in dogs associated with potentiated sulfonamides include hypothyroidism, keratoconjunctivitis sicca, neutropenia, hepatopathy and polyarthritis.
High levels of resistance to tetracyclines exist in S. pseudintermedius; therefore, this class of antibiotics cannot be regarded as a good empirical choice. Yet, doxycycline has been used effectively to treat bacterial skin infections caused by susceptible strains. Therefore, because of its narrow spectrum of action, doxycycline would be a good first-line antibiotic choice based on culture and susceptibility results.
Many people use first-generation cephalosporins (cephalexin, cefadroxil) as first-line antibiotics. These antibiotics are bactericidal and have a broad spectrum of action but primarily target gram positive bacteria. Resistance to this class of antibiotics is only now being identified. Ideally, use of these antibiotics should be reserved for those cases in which culture and susceptibility indicate they are the antibiotic of choice. For cases in which there have been multiple antibiotic exposures (e.g. recurrent infections) and success of other antibiotics is questioned, then first-generation cephalosporins can be used empirically.
Two third-generation cephalosporins, cefovecin and cefpodoxime proxetil, have recently been registered in the USA and Europe. Cefovecin is a long-acting injectable antibiotic which lasts 14 days and cefpodoxime proxetil is an oral antibiotic that can be administered once daily. While both drugs offer good activity against staphylococci, their activity against S. pseudintermedius is not superior to first-generation cephalosporins. In addition, they are active against a wide range of Gram-negative bacteria. Therefore, their use has the potential for selection of both methicllin resistance in staphylococci and multi-resistant E. coli. In spite of their convenient dosing, these drugs should only be used as first-line antibiotics if compliance is anticipated to be a problem.
Amoxicillin with clavulanate is also a broad-spectrum bactericidal antibiotic that primarily targets Gram-positive bacteria. It, too, should be reserved for those cases of pyoderma in which culture and susceptibility indicate it is the preferred antibiotic. In addition, it can be used empirically similar to first-generation cephalosporins.
Second-line antibiotics should be based solely on culture and susceptibility results. Antibiotics included here include chloramphenicol, rifampin, and amikacin. Chloramphenicol is a bacteriostatic, narrow spectrum antibiotic. While it meets the criteria to be a first-line antibiotic, it is reserved for treatment of methicillin resistant S. pseudintermedius which are sometimes only susceptible to this antibiotic. Chloramphenicol is administered three times daily. In addition to this inconvenient frequency of administration, it often causes gastrointestinal disturbances, is associated with drug interactions, and may cause bone marrow suppression.
Rifampin is a bactericidal antibiotic with excellent tissue penetration. It has a broad spectrum of activity against many Gram-negative and most Gram-positive microorganisms and is the most active antibiotic known against staphylococci. Resistance to rifampin readily develops with monotherapy; therefore, it is best to use in combination with another antibiotic such as clindamycin or cephalexin. Rifampin is potentially hepatotoxic and this side effect appears to occur more commonly in dogs than in people. Mild increases in alkaline phosphatase activity occur frequently and appear to be benign; however, treatment should be discontinued if there are concurrent increases in other hepatic enzyme activities. Other rare signs associated with rifampin administration in dogs include thrombocytopenia, hemolytic anemia, anorexia, vomiting, diarrhea, and death.
Amikacin is an aminoglycoside that is not typically considered for treating dogs with skin infections. It is an injectable antibiotic and is nephrotoxic. Therefore, use of this antibiotic is only based on culture and susceptibility results wheo other antibiotic would be effective.
Third-line antibiotics should be chosen last because of the pressure they place on bacteria in terms of selecting for antimicrobial resistance. These include the third-generation cephalosporins (see above) and fluoroquinolones. While staphylococci often are susceptible to fluoroquinolones, resistance develops rapidly. In addition, fluoroquinolone use appears to select for methicillin resistance. Use of this class of antibiotics should be preserved for cases of deep infections associated with Gram-negative organisms.
Topical therapy
Topical therapy may be used as both an adjunct to systemic therapy or, in some cases, as the sole therapy for cutaneous skin infections. Topical therapy includes whirlpool baths, especially for dogs with deep pyodermas, and antibacterial shampoos. Chlorhexidine, benzoyl peroxide, and ethyl lactate containing shampoos all have demonstrated beneficial responses in dogs with infections. Bathing should be done two to three times per week with a 10 minute contact time. In a study using topical therapy alone to treat superficial pyodermas, 50% of the cases were treated effectively when bathed three times per week. In cases of recurrent or resistant infections, a topical chlorhexidine spray is very beneficial when used once to twice daily.
Focal lesions can be treated with chlorhexidine spray, mupirocin ointment, benzoyl peroxide gel, or fusidic acid (not available in the USA).
Duration of therapy
Length of therapy depends of the depth of infection and is determined by clinical cure. For superficial infections the average duration of therapy is 3 to 4 weeks with treatment continued 1 week past clinical cure. For recurrent superficial infections the average duration of therapy is a bit longer and is continued for 10 to 14 days past clinical cure. Deep infections require 6 to 12 weeks of antibiotics with treatment continued 2 weeks past clinical cure. If lesions recur within 1 week after discontinuing therapy, it is likely that treatment was not long enough.
In order to determine if clinical cure is achieved, the dog should be re-examined before the antibiotic course is completed. Discontinuation of therapy too soon leads to the selection of resistant bacteria. A common reason why pyodermas fail to respond to treatment or recur is if the length of therapy is too short.
BACTERIAL SKIN INFECTIONS
The 28th most common diagnosis in hospitalized patients. Cellulitis, impetigo, and folliculitis are the most common bacterial skin infections seen by the family physician. The percentage of office visits for cellulitis was 2.2 percent, and for impetigo, it was 0.3 percent, in a cohort of almost 320,000 health plan members (data taken from primary physician diagnosis codes from January 1, 1999 to December 1, 1999 for Intermountain Health Care, Salt Lake City). Knowledge of the presentation, histopathology, and microbiology for each type of infection is important for proper care of the patient.
IMPETIGO
Impetigo is most commonly seen in children aged two to five years and is classified as bullous or nonbullous. The nonbullous type predominates and presents with an erosion (sore), cluster of erosions, or small vesicles or pustules that have an adherent or oozing honey-yellow crust. The predilection for the very young can be remembered by the common lay misnomer, “infant tigo.” Impetigo usually appears in areas where there is a break in the skin, such as a wound, herpes simplex infection, or maceration associated with angular cheilitis, but Staphylococcus aureus can directly invade the skin and cause a de novo infection.
The bullous form of impetigo presents as a large thin-walled bulla (2 to 5 cm) containing serous yellow fluid. It often ruptures leaving a complete or partially denuded area with a ring or arc of remaining bulla. More than one area may be involved and a mix of bullous and nonbullous findings can exist. Nonbullous impetigo was previously thought to be a group A streptococcal process and bullous impetigo was primarily thought to be caused by S. aureus. Studies now indicate that both forms of impetigo are primarily caused by S. aureus with Streptococcus usually being involved in the nonbullous form. If the infection is a toxin-producing, phage group II, type 71 Staphylococcus (the same toxin seen in Staphylococcus scalded skin syndrome, a medical emergency where large sheets of the upper epidermis slough off), large bullae will form as the toxin produces intradermal cleavage. Otherwise, smaller bullae develop and the honey-crusted lesions predominate.
A study published in 1990 concluded that topical mupirocin (Bactroban) ointment is as effective as oral erythromycin in treating impetigo. However, because the lesions of bullous impetigo can be large and both forms of impetigo can have satellite lesions, an oral antibiotic with activity against S. aureus and group A beta-hemolytic streptococcal infection is warranted ionlocalized cases. Because of developing resistance, erythromycin is no longer the drug of choice. Azithromycin (Zithromax) for five days and cephalexin (Keflex) for 10 days have been shown to be effective and well-tolerated. Dicloxacillin (Pathocil), oxacillin (Prostaphlin), first-generation cephalosporins, or amoxicillin-clavulanate are also acceptable alternatives. Broad-spectrum fluoroquinolones have also been shown to be effective, and several have been approved by the U.S. Food and Drug Administration for treating skin and soft tissue infections. These medications have excellent skin penetration and good bioavailability, but no generic forms are currently available, and they are only approved for use in adults.
As with other diseases involving Streptococci, there is a small chance of developing glomerulonephritis, especially in children aged two to six years. Presenting signs and symptoms of glomerulonephritis include edema and hypertension; about one third of patients have smoky or tea-colored urine. Streptococcal glomerulonephritis usually resolves spontaneously although acute symptoms and problems may occur. Impetigo can be spread by direct person-to-person contact, so appropriate hygiene is warranted. Nasal carriage of S. aureus has been implicated as a source of recurrent disease and can be reduced by the topical application of mupirocin twice daily for five days.
FOLLICULITIS
Hair follicles can become inflamed by physical injury, chemical irritation, or infection that leads to folliculitis. Classification is by the depth of involvement of the hair follicle. The most common form is superficial folliculitis that manifests as a tender or painless pustule that heals without scarring. The hair shaft will frequently be seen in the center of the pustule. Multiple or single lesions can appear on any skin bearing hair including the head, neck, trunk, buttocks, and extremities. Associated systemic symptoms or fever rarely exist. S. aureus is the most likely pathogen; however, commensal organisms such as yeast and fungi occasionally appear, especially in immunocompromised patients. These lesions typically resolve spontaneously. Topical therapy with erythromycin, clindamycin, mupirocin, or benzoyl peroxide can be administered to accelerate the healing process.
Staphylococci will occasionally invade the deeper portion of the follicle, causing swelling and erythema with or without a pustule at the skin surface. These lesions are painful and may scar. This inflammation of the entire follicle or the deeper portion of the hair follicle (isthmus and below) is called deep folliculitis. Oral antibiotics are usually used in the treatment and include first-generation cephalosporins, penicillinase-resistant penicillins, macrolides, and fluoroquinolones.
Gram-negative folliculitis usually involves the face and affects patients with a history of long-term antibiotic therapy for acne. Pathogens include Klebsiella, Enterobacter, and Proteus species. It can be treated as severe acne with isotretinoin (Accutane), but use of isotretinoin is associated with major side effects, including birth defects.
“Hot tub” folliculitis is caused by Pseudomonas aeruginosa contamination of under-treated water in a hot tub or whirlpool. Multiple pustular or papular perifollicular lesions appear on the trunk and sometimes extremities within six to 72 hours after exposure, and mild fever and malaise may occur. Lesions in the immunocompetent patient typically resolve spontaneously within a period of seven to 10 days. Treatment is directed at prevention by appropriately cleaning the whirlpool or hot tub and maintaining appropriate chlorine levels (bromine and copper solutions are less common alternatives) in the water.
FURUNCLES AND CARBUNCLES
Furuncles and carbuncles occur as a follicular infection progresses deeper and extends out from the follicle. Commonly known as an abscess or boil, a furuncle is a tender, erythematous, firm or fluctuant mass of walled-off purulent material, arising from the hair follicle. These lesions may occur anywhere on the body, but have a predilection for areas exposed to friction. Furuncles rarely appear before puberty. The pathogen is usually S. aureus. Typically, the furuncle will develop into a fluctuant mass and eventually open to the skin surface, allowing the purulent contents to drain, either spontaneously or following incision of the furuncle.
Carbuncles are an aggregate of infected hair follicles that form broad, swollen, erythematous, deep, and painful masses that usually open and drain through multiple tracts. Constitutional symptoms, including fever and malaise, are commonly associated with these lesions but are rarely found with furuncles. With both of these lesions, gentle incision and drainage is indicated when lesions “point” (fluctuant or boggy with a thin shiny appearance of the overlying skin); caution should be taken to not incise deeper than the pseudo capsule that has been built at the site of infection. Loculations should be broken with a hemostat. The wound may be packed (usually with iodoform gauze) to encourage further drainage. In severe cases, parenteral antibiotics such as cloxacillin (Tegopen), or a first-generation cephalosporin such as cefazolin (Ancef), are required. The physician should be aware of the potential for gas-containing abscesses or necrotizing fasciitis, which require immediate surgical debridement.
Final Comment
The majority of bacterial skin infections are caused by the gram-positive bacteria Staphylococcus and Streptococcus species. Antibiotics are used empirically with consideration for resistance patterns. Current antibiotic recommendations include penicillinase-resistant penicillins, first-generation cephalosporins, azithromycin, clarithromycin, amoxicillin-clavulanic acid, or a second-generation fluoroquinolone in the skeletally mature patient. Gram-negative coverage with a second-, third-, or fourth-generation cephalosporin is usually indicated in children under three years and in patients with diabetes or who are immunocompromised.
