II. Mammary Fibroadenoma
III. Ringtail
IV. Staphylococcal Dermatitis
A. Radfordia ensifera is a host-specific mite closely related to Myobia musculi and Radfordia affinis of mice.
1. Life Cycle: The life cycle, transmission, and pathologic effects are unknown, but presumably are similar to those of Myobia musculi of mice.
2. Diagnosis: Visualization of the mites on cervical hairs
with the aid of a dissecting microscope is done in diagnosing rat as well
as mouse mites. 
3. Treatment: Treatment and control of the infestation
is the same as for Myobia musculi of mice. Ivermectin at 0.2
mg/kg subQ may be effective when administered every 2 to 3 weeks for a
total of 3 treatments.
B. Polyplax spinulosa (Spined Rat Louse)
1. Transmission: The louse lives its entire life cycle on the rat. Direct contact is the method of transmission. The parasite is rarely seen in research rats, but is common in wild rats.
2. Clinical Signs: Scratching, restlessness, and debilitation occur in heavy infestation.
3. Pathological Effects: The louse is a blood sucker and can cause anemia.
4. Diagnosis: Identification of adult lice, nymphs, or eggs on the fur provides the diagnosis.
5. Treatment: Adults and weanlings can be dusted once a week with pyrethroids or pyrethrin dusts. Ivermectin may also be effective at a dose of 0.2 mg/kg subQ administered every 2 to 3 weeks for 3 treatments.
6. Control: Regular examinations and treatments may eventually rid the colony of lice.
This is the most common tumor of rats. Because of the extensive
mammary tissue present in rats, tumors may be found practically anywhere--behind
the shoulder blades, at the base of the tail, etc. Tumors may occur
in males as well as in females. The tumors, which appear as subcutaneous
lumps, may be quite extensive (photo on left). Ulceration and subsequent
dermatitis occur frequently. Mammary tumors are usually encapsulated
and benign. Occasionally mammary adenocarcinomas are diagnosed from excisional
biopsies. With surgical removal, the prognosis is good, although recurrence
in another location is common. Histologically, both fibrous an dglandular
components are hyperplastic (photo on right). The progression of
either the glandular or fibrous component to malignancy is rare.
Insufficient environmental humidity (<20%), artificially increased
temperature and drafts predispose this condition. Other physiological factors (age, hydration,
nutritional status, and genotype) can also be involved. Annular constriction
of the tail is observed in young (suckling and weanling) rats. Necrotic tails may slough.
Diagnosis is made via clinical signs and history of low environmental humidity.
There is no treatment for affected rats. Tail stumps usually heal
without complication. Prevention of ringtail is accomplished by providing
sufficient environmental humidity, reducing drafts, and maintaining room
temperatures between 70oF to 74oF. 
A syndrome of ulcerated to scabby skin lesions on the dorsal cervical
or cranial regions occur frequently in some rat colonies (A.). This
syndrome appears to be seasonal with most cases occurring in the spring
and occasionally the fall. Trauma to the skin from fighting, scratching,
etc. is thought to be an inciting factor. In colonies of rats on
dermal toxicity studies, the shaving of the skin as well as the substance
application provides the skin irritation necessary to initiate scratching.
In many cases, Staphylococcus sp., including S. aureus and
S.
epidermidis, have been isolated from the wounds. Since Staphylococcus
sp.
can be frequently isolated from the nasopharynx and feces of rats with
dermatitis, the fastidious grooming and scratching activities of the rat
provide a constant source of staphylococcal inoculum for the wound.
The skin lesions are excoriations of varying sizes with a serous to sanguinous
discharge. Successful treatment of the dermatitis with topical antibiotic
or antibiotic/steroid ointments has been reported. Combination therapy
of oral benadryl (10 mg/kg) and chloramphenicol (50 mg/kg) has resulted
in resolution of ulcerative lesions. Length of therapy may be prolonged
if the initial irritating stimulus is not corrected. Clipping
toenails of the hind foot has allowed healing of the wounds without antibiotic
therapy.
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