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Staphylococcus
spp
Infection: |
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S
aureus
and
S
epidermidis
are gram-positive bacteria commonly found on the skin of most animal species, including mice and rats. In rats, ulcerative dermatitis may be observed on the head and neck, often secondary to skin trauma from fighting or scratches. Cutaneous infection in nude mice may lead to conjunctivitis and facial abscesses. Abscesses occasionally enlarge and form disfiguring subcutaneous lumps around the face and head (furunculosis). Treatment includes topical antibiotic or
antibiotic/steroid ointments. Therapy may be prolonged without correcting the irritant stimulus, and immunosuppressed animals do not respond well. Clipping toenails of the hindfoot helps prevent further damage caused by scratching. |
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Corynebacterium
bovis
Infection: |
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C
bovis
causes scaly skin hyperkeratosis in nude mice. With the exception of other hairless strains, most infected immunocompetent mice are asymptomatic. Bacteria can be present on the skin or in the oral cavity, and transmission occurs by direct contact and fomites. Clinically, affected mice have weight loss, pruritus, and transient hyperkeratosis, primarily along the dorsum. Mortality is low. Diagnosis is based on isolation of the causative organism, PCR for bacterial
antigen, gross lesions, and histopathology. Treatment with ampicillin or penicillin may help alleviate clinical signs. |
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Dermatophytosis (Ringworm): |
| Fungal skin infections occur infrequently in mice and rats. The most commonly isolated dermatophytes are
Trichophyton
and
Microsporum
spp
. Infection is often asymptomatic or characterized by small, patchy areas of alopecia with reddened margins, dermatitis, and flaky exfoliation. Transmission occurs by direct contact or on fomites such as cage bedding. Diagnosis is based on lesions, Wood’s lamp examination, isolation of fungus in or on infected hairs, and histology of lesions with a silver stain. Effective treatment includes topical fungicidal ointments, clipping hair from affected areas,
povidone-iodine scrubs, or oral griseofulvin (25 mg/kg for 30-60 days). Ringworm is contagious to humans and other animals. |
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Acariasis: |
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Several mites may infest the skin and fur of mice, most often
Myocoptes
musculinus
and
Myobia
musculi
and less frequently,
Radfordia
affinis
and
Psorergates
simplex
. The most commonly reported rat fur mite is
R
ensifera
. Transmission is by direct contact. Clinically, rodents may be asymptomatic, or with heavy infestation, demonstrate constant scratching leading to self-induced skin trauma, alopecia, and ulcerative dermatitis. Black-haired mice are reported to be more sensitive to infection. Mites spend their entire life cycle on the host. Lesions are often found along the head and neck and between the shoulder blades. Chronic cases sometimes develop secondary bacterial infections.
Diagnosis is accomplished by direct observation of mites or eggs from hair and skin of dead or anesthetized mice. As pelts of recently deceased mice cool to room temperature, mites will crawl up to the tips of the hairs, appearing as white specks. Treatment includes application of silica or pyrethrin dusts, ivermectin solutions in drinking water (equine preparation at 8 mg/L drinking water once a week for 3 wk), or 0.1% ivermectin solutions applied topically. Caution should be
exercised (eg, testing) before colony treatment because ivermectin may be toxic in certain strains of mice. Repeat treatments should account for the mite’s life cycle. Unhatched eggs may lead to reinfection. |
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Pediculosis: |
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Polyplax
spinulosa
and
P
serrata
are blood-sucking lice commonly encountered in wild rats and mice, but rarely seen in laboratory rodents. The lice spend their entire life cycle in the host and transmission occurs by direct contact. Clinical signs with heavy infestation include pruritus, restlessness, debilitation, and anemia. Diagnosis is based on identification of adult lice, nymphs, or eggs on the fur. Treatment and control area similar to mite infection (see above). |
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Fleas: |
| Rodent fleas (
Xenopsylla
and
Nosopsylla
spp
) are uncommon in laboratory or pet rats and mice, but can signal contamination by wild rodents. They are also important potential vectors of zoonotic disease such as
Yersinia
pestis
,
Rickettsia
typhus
, and
Rodentolepis
nana
tapeworms. Diagnosis is based on identification of fleas on affected rodents. Treatment includes carbaryl dusts or pyrethrin sprays and preventing wild rodent contamination. |
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Ringtail: |
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Low environmental humidity, high temperatures, and drafts predispose young rats and mice to develop annular constrictions of the tail and occasionally feet or digits. Localized edema can lead to dry gangrene and tissue sloughing. Diagnosis is based on clinical signs and history. Treatment is supportive, and tail stumps usually heal without complication. Prevention is accomplished by providing environmental humidity of 40-70%, reducing drafts,
and maintaining room temperatures at 70-74°F (21-23°C). |
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Barbering: |
| Barbering is an abnormal behavior frequently observed in groups of male or female mice and occasionally rats. Dominant members of the group chew the hair and whiskers of subordinates. Affected areas around the face or anterior dorsum appear clean shaven, although the underlying skin is normal. Treatment consists of removing the dominant mouse that has not been barbered. |
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Fight Wounds: |
| Mice and rats, usually males, often fight and cause trauma to the face, back, and genital areas. Clinically, the skin may have focal alopecia and scabs. Affected mice lose weight and sometimes die. Secondary bacterial infection and abscesses may occur. Tail biting can lead to gangrene and sloughing. Treatment includes cleaning the wounds with povidone-iodine solution, lancing and draining abscesses, and appropriate topical antibiotic ointments. Aminoglycosides are toxic and
should be avoided. Control is achieved by separating affected mice. |
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