This article is from the Sep./Oct. 1991 AFRMA Rat & Mouse Tales news-magazine.

Internal and External Parasites of Rats and Mice

By Carmen Jane Booth
Domestic rats and mice are hosts to far fewer parasites than their wild counterparts, because husbandry practices interrupt complex life cycles. It is imperative that feed, bedding, and water remain uncontaminated with urine and feces from wild rats, mice, birds, insects, and domestic cats in order to prevent cross contamination and infection since some parasites require multiple hosts (different species) to complete their life cycle. In addition, some parasites are nonpathogenic (do not cause disease) in some hosts, but are highly pathogenic in others. Only the more common parasites will be discussed here since treatment is often the same and some are difficult to diagnose.

Internal: Endoparasites

For the parasites that shed eggs in the feces, a fecal flotation and microscopic exam can be done to demonstrate the presence of infection. For Syphacia species, the scotch tape test can be done—take a piece of tape and press it a few times in the perianal region and look under a microscope for the presence of eggs. Many of these parasites can be diagnosed post mortem (after death) but become impossible to find if many hours have passed since the animal died.

*Potential Zoonosis, i.e. can infect humans

External: Ectoparasites - Diagnosis - skin scrapings, scotch tape test, histology

All of these lice and mites spend their entire life cycle on the host except for O. bactoi. The common signs include: itching (pruritus), hair loss (alopecia), blood loss (anemia), skin irritation (dermatitis), unthriftiness, restlessness, and rough hair coat. In order to get rid of these beasts, the life cycle must be disrupted for those that spend their life on the host, and the environment treated for those that can live off the host. A new treatment not listed in the tables is Ivermectin 400 micrograms/kilograms subcutaneously two treatments two weeks apart. This is not a federally approved use for Ivermectin, but can be done by your veterinarian. The ivermectin needs to be diluted in sterile saline to meet the dose requirement.

I personally had my rat Poly treated with Ivermectin for her pruritus and rough hair coat. I had done numerous skin scrapings and scotch tape tests to try and find evidence of parasites and was unsuccessful. My dermatology professor advised me to treat her and see if she improved. Poly is no longer scratching and her coat looks great.

Included are 2 tables with treatment protocols from a 1984 text.

Table 1 - RATS
Selected Treatment Regimens for Common Parasites ^a,b

^a Information kindly supplied by Dr. J. W. Streett, Yale university.
^b A number of these compounds have adverse effects on the experimental usefulness of treated rats and therefore should be used with discretion and full knowledge of the investigator.

Table 2 - Mice
Reported Treatment for Ectoparasitism of Laboratory Mice ^a

^a From Weisbroth (1982).

(Anyone suspecting their animal(s) of having a medical problem should seek the care of their local veterinarian.)

From Donna Galins, Brea, CA
I had a rat named Cynder. She was about l½ years old. I never bred her and she shared a cage with another rat, also l½ years old and never bred. The other rat’s name was Blossom.

Back in January of 1991, I found blood in the cage. I was not able to find out which rat, if either, was bleeding or injured. Also at that time, Blossom’s mammary gland (first left) was swelling and looked white. I took her to the vet thinking that maybe she was the one that was bleeding. The doctor took a sample of the liquid from the mammary gland. We didn’t know what to think. The vet drew all of the fluid out and she seemed to be all right.

When I went to place her back in the cage and found more blood, it was then that I knew it must be from Cynder. I picked her up and discovered blood on her rear end. After discussing the situation with the vet, he didn’t know what the problem could be. The bleeding continued off and on for a few months. However, she was eating, eyes very alert, active, gaining weight, and generally doing well. During this time, Blossom’s mammary continued filling with white liquid and getting bigger. We kept draining the gland, finally discovering that the fluid was milk. For an unknown reason she was producing milk, with all the other glands showing the same thing.

She then began to drag Cynder around the cage, attempting to “mother” her. I didn’t know what to do for her. We kept draining her glands, trying to make her more comfortable. Finally, I talked with Karen and she suggested that I give her some babies to nurse. I did this, but all she did was drag them around the cage, never nursing them. Her mammary glands continued to swell.

Cynder was bleeding worse during this time. Her body started to feel mushy, but was still alert, eyes clear, and eating. I had decided it was time to put them to sleep—it was a very sad thing to do. We did a necropsy on Cynder and we found that she had a very bad infection called pyometra (an infection of the uterus). There was a large mass and another one growing.

I was glad I made the decision to put Blossom and Cynder to sleep. I will always remember them with a happy heart and will miss them.

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