Background: Oxyuriasis, pinworms; are a
persistent problem of well-managed animal colonies.
Pinworms that commonly infect laboratory colonies
include Syphacia muris, S. obvelata, and Aspiculuris
tetraptera.
Transmission: The pinworm life cycle is direct. Adult
worms inhabit the colon and cecum. Eggs are shed in
the feces or deposited on the perianal region of the
rodent. The eggs are very light and aerosolize easily
facilitating infection. Embryonated eggs are ingested,
resulting in infection.
It has been shown that embryonated eggs can
survive at room temperature for extended periods of
time.
Clinical Signs: Clinical signs are related to the
parasite burden in a particular animal. In general,
weanling animals and males tend to be more heavily
parasitized.
The infection is usually subclinical, with no
apparent clinical signs. However, infected mice can
develop rectal prolapses, intussusceptions, fecal
impactions, poor weight gain, rough hair coats, bloody
feces, and perianal irritation. The disease is usually
more severe in athymic nude mice.
Diagnosis: Diagnosis is usually based on identification
of the parasite eggs in a fecal flotation (Aspiculuris sp.)
or by examining a tape test (Syphacia sp.). Adult
worms can also be seen with direct examination of
the cecum and colon with a dissecting microscope.
Effects on Research: Pinworm infections have
resulted in significantly higher antibody production to
sheep red blood cells, reduced occurrence of
adjuvant-induced arthritis, and impaired intestinal
electrolyte transport. As athymic nude mice are more
susceptible to these infections, increased morbidity
can interfere with research using infected mice.
Prevention: To prevent this disease, obtain
replacement stocks from sources that are known to
be free of disease. Personnel working with infected
animals should not enter rooms that contain naïve
animals.
All animals should be placed in microisolator
caging environments that are handled with the aid of
a laminar flow hood using sterile techniques during
handling and observation of the animals.
Eradication: Currently there are two widely accepted
medication regimens for eradicating pinworms from
rodents: ivermectin or fenbendazole. Both methods
have advantages and disadvantages for the
researcher, animal and animal care staff.
Ivermectin is either applied topically to the
perineum of the affected animals or administered in
the drinking water. Although ivermectin is not
expensive, this treatment regiment is extremely labor
intensive. All animals need to be handled daily for 7 to
10 days if it is being applied topically. MI bottles need
to be changed daily for 7 to 10 days if it is being
administered in the water. Ivermectin can interfere
with neurological function and is generally not
recommended in colonies doing behavioral research.
Fenbendazole is administered orally through
specially prepared rodent chows. These diets are
expensive when compared to normal rodent diets.
Typically, the rodents are fed the diet containing
fenbendazole for at least four 7 to 10-thy treatment
periods with intervening 7 to 10-day periods of
feeding with non-medicated chow. Alternatively, the
diet may be given for 6 weeks straight. Fenbendazole
may interfere with liver function, making it an
undesirable choice for studies that require normal
liver function,
Regardless of medication selected, increased
sanitation should be practiced. All caging, equipment,
and room surfaces should be disinfected as directed
by the veterinarian. Generally, compounds such as
chlorine disinfectants and quatemary ammonia
compounds are recommended. Autoclaving and
power washing may also be of benefit.
A recent study (Huerkamp, 2000) suggests that if
five fenbendazole treatment periods are used (for a
total of 9 weeks of treatment) to treat Syphacia,
intensive sanitation may not be required for colonies
of rats. This is promising information, but may not be
applicable to Aspiculuris sp. or infections in mice.
Further information is required before this can be
uniformly recommended, but this method may be
suggested by the veterinary staff.
References:
Baker, DG. 1998. “Natural Pathogens of Laboratory Mice, Rats,
and Rabbits and Their Effects on Research.” Clinical Iviicrobiology
Reviews. 11:231-266.
Huerkamp, MJ etal. 2000. “Fenbendazole treatment without
environmental decontamination eradicates Syphacia muris from all
rats in a large, complex research institution.” Contemporary Topics.
39(3): 9-12.
This document has been excerpted from the Division of Laboratory Animal Resources University of Illinois and is used by permission. |
