Page 555 - The Veterinary Laboratory and Field Manual 3rd Edition

492 Susan C. Cork

trichinosis Signs in animals: Initially there may be few
signs. Later in the disease the animal may have
Cause: Trichinella spiralis enlarged lymph nodes and become thin. In the
pulmonary form the animal may show respira-
Epidemiology: This is a nematode helminth that tory signs with coughing and laboured breathing.
is common in the muscles of pigs, wild boar and
other omnivores including rodents and bears. Diagnosis: The tuberculin test (a skin fold test)
Humans and other omnivores become infected by may be used to diagnose the infection in live
eating meat infected with tissue cysts of T. spiralis. animals. It must be mentioned, however, that
infection with non-pathogenic environmen-
Signs in animals: There may be none. There tal Mycobacteria spp., for example, M. avium
will be cysts in the muscles which may cause a may cause false positive results on this test so
transient myositis. In some animals, including advice should be sought from a veterinary offi-
humans, there will be an initial gastroenteritis cer on performing and interpreting the results
after consumption of the meat followed by signs of the tuberculin test. Most diagnoses of bovine
of anaphylactic shock up to 2 weeks later when tuberculosis are made at post-mortem or meat
the helminth larvae migrate through the tissues. inspection. Send fresh and fixed tissues to the
There will be fever, headache and vomiting. laboratory (especially enlarged lymph nodes).
Diagnosis: The cysts in meat can be identified at Microscopy and culture should be performed
official meat inspection but need to be followed where possible and feasible. Molecular tech-
up by trichinoscopy at the veterinary laboratory. niques are also commonly used. Some serological
An ELISA test and molecular tools are also now screening tests are also under development but
available to screen meat for this parasite. the performance of these is highly variable.
Control: Tuberculin testing and quarantine pro-
Control: Official meat inspection (including pork, cedures. Treatment should not be attempted.
horse meat and game). Cook meat well before Milk should be boiled before consumption
eating (note that drying and smoking meat does by humans and all meat should be officially
not kill T. spiralis). Do not feed pigs uncooked inspected. Note that in countries where human
waste food. Control rodents in the piggery. tuberculosis is endemic livestock may become
infected with Mycobacterium tuberculosis. In Asia,
human tuberculosis is prevalent in domesticated
tuberculosis elephants and other species.

Cause: Mycobacterium bovis. Epidemiology:
Mycobacterium bovis is an obligate intracellular bac- typhus
terium most commonly identified in cattle but
it also infects deer and other ungulate species. Cause: Rickettsia species
Wildlife may also be important for the transmis- Epidemiology: Most of the agents causing
sion of the bacterium from one area to another. typhus are transmitted by an arthropod vector.
Once the disease becomes endemic in wildlife it Tick typhus (Rickettsia conori) and scrub typhus
is very hard to eradicate. The organism may be (Orienta tsutsugamushi) are transmitted to humans
located in focal areas in the liver, lungs and lymph by various tick and mite species (respectively)
nodes at post-mortem. Humans may be infected by from wildlife reservoirs (especially rabbits,
drinking unpasteurized milk from an infected cow rodents, also quail). Human typhus (epidemic
or when handling or consuming infected meat. typhus; R. prowazekii) is now less common. It is

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