II. Cestodes
III. Nematodes
IV. Arthropods
Spironucleus muris and Giardia muris are protozoa that colonize the upper small intestine; Spironucelus muris dwells in the mucosal crypts of the small intestine and in the pylorus, and Giardia muris resides along the villous enterocytes in the anterior small intestine. Trichomonads can be found in the lower small intestine and the large intestine. Ingestion of infective cysts is the primary mode of transmission. Infected adult rats are clinically unaffected. Direct smears of the small intestinal contents can be performed to look for the fast darting motility of Spironucleus and "tumbling leaf" motility of Giardia. Trichomonads have a wobbly motility and the action of the undulating membrane can be easily observed. Cysts can be detected in the feces. Dimetridazole (1mg/ml) or metranidazole (2.5 mg/ml) in drinking water has been reported to decrease the parasite load, but does not eliminate the infection.
A. Rodentolepis nana (dwarf tapeworm) and Hymenolepis diminuta (the rat tapeworm) can infect rats. However, the incidence of infection is rare. For information about these parasites, please see the Hamster Parasitic Disease section.
B. Taenia taeniaformis - Rats serve as intermediate
hosts for the cat tapeworm Taenia taeniaformis. The cysticercoid
cyst (Cysticercus fasciolaris) embeds in the liver and may cause
a palpably enlarged liver if cysts are numerous. Infection occurs
when rats ingest ova in rat food or bedding contaminated with cat feces.
No treatment is necessary but prevention of feline fecal contamination
of rat food or bedding is required. This infection uncommonly occurs
in research facilities since bedding and food sources and storage practices
prevent cat fecal contamination.
A. Syphacia muris (Rat Pinworm)
1. Transmission: Syphacia muris deposits eggs in the perianal region. Transmission of infection occurs via ova ingestion. The eggs are very light and have been shown to aerosolize, resulting in widespread exposure. The incidence of infection is high.
2. Clinical Signs: No signs are usually seen. It has been reported that heavy parasite loads may lead to catarrhal enteritis, or perianal irritation causing hair to be chewed off the tail base.
3. Diagnosis: Direct exam of cecal contents, fecal flotation,
and tape test of the perianal region will identify adults and eggs, respectively.
The eggs are slightly smaller and more symmetrical than those of Syphacia
obvelata.
5. Treatment: If treatment is desired, piperazine (4 to 7 mg/ml water) for 3 to 10 days is effective. Karo syrup can be added to the solution if the rats refuse to drink it. Fenbendazole medicated feed provided every other week for 5 weeks has been an effective treatment method. Other successful treatments include ivermectin at 0.2 mg/kg subQ weekly for 2 to 3 weeks or in drinking water (25 mg/liter) for 4 to 5 daily treatments 3 days apart.
6. Control: Prevention and control of infection are often difficult. Rigid sanitary procedures, use of filtered cage tops to prevent aerosol transmission, and regular ova examinations with treatment may control the parasitism.
B. Syphacia obvelata and Aspiculuris tetraptera pinworms may transiently infect rats. The comments made about Syphacia muris also apply to Syphacia obvelata, with which it is frequently confused. Aspiculuris tetraptera inhabits the colon and deposits its eggs in the feces; thus, it cannot be diagnosed by use of the anal tape test. Treatment is the same as for Syphacia muris.
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.
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