dog and cat assay data sheet
Toxoplasma gondii
Test code: X0002
- Qualitative
detection of Toxoplasma gondii by PCR
Toxoplasmosis is the most common parasitic
infection worldwide affecting humans and a number of domestic
animals. The organism that causes toxoplasmosis is Toxoplasma
gondii - a single-celled organism.
The cat is the only animal in which sexual
reproduction of the organism occurs. Thus, cats are the only
domestic animal that has the potential to shed the organism’s
eggs. Although there is generally a high prevalence of
infection in cats, most surveys show a less than 1% incidence
of oocyst shedding. This is to be expected as infected cats
generally do not re-shed oocysts following their first
exposure to Toxoplasma gondii.
Dogs may transmit Toxoplasmosis to humans by
rolling in foul-smelling substances and by ingesting fecal
material. The fact that 50% of stray dogs and cats carry T. gondii antibodies suggests that they have been infected with
the parasite. Reports show that dogs in shelters, dogs living
in close contact with wild birds and rodents in rural areas,
and dogs fed raw meat are at much higher risk for being
infected by T. gondii.
Despite the high prevalence of Toxoplasma
gondii infection, significant clinical disease in cats (and
other species) appears to be very rare. This implies that many
infected animals can be carriers of the parasite with
unnoticed symptoms. When disease does occur, it may develop
either following primary infection due to an inadequate immune
response to stop the invasive tachyzoites, or as a result of
reactivated infection due to compromised immunity. Clinical
disease appears to be most common in young cats (less than 2
years of age), and this may be due, in part, to a poorly
developed immune response in these cats. Reactivation of
infection in older cats may be linked to co-infection with
feline leukemia virus or feline immunodeficiency virus in some
cats. The most commonly reported clinical signs associated
with feline toxoplasmosis are anorexia, weight loss, lethargy,
dyspnea (due to pneumonia), ocular signs (iritis,
chorioretinitis) and pyrexia. Other less common features
include gastrointestinal signs (vomiting and diarrhea),
neurological signs, lymphadenopathy, jaundice, myositis and
abortion.
Toxoplasmosis presents a serious health risk
for people living in close contact with these animals.
Infection is especially dangerous for people with suppressed
immune system, such as AIDS and cancer patients, and for
pregnant women. Swollen glands and fever are the most common
findings in those who have any symptoms. Infected infants may
show various symptoms including jaundice, encephalitis, mental
defects, and eye disease.
The diagnosis of toxoplasmosis is
problematic and a definitive diagnosis rests on demonstration
of the active form of the organism in tissues taken at post
mortem examination or in biopsy samples. Laboratory tests may
also be used as diagnostic aids. The “gold standard” for the
detection of T. gondii in clinical specimens is mouse
inoculation and then the detection of T. gondii-specific
antibodies. This method is sensitive and specific but very
time-consuming, taking up to six weeks to obtain a diagnosis.
Cell culture detection of this parasite is also slow and lack
sensitivity. An ELISA test may be used, but is difficult in
animals with severe immune dysfunction. Furthermore,
serological tests cannot detect cats that are shedding the
parasite in their feces. Molecular detection by PCR method
overcomes these difficulties and provides a highly sensitive
and specific determination of an animal’s infection status.
Utilities:
- Confirm the disease causing agent
- Ensure that animal groups are free of T. gondii
- Early prevention of spread of this
parasite among a group of animals
- Minimize human exposure to this parasite
References:
Dubey, J.P. (1993) Toxoplasma, Neoplasma, Sarcocystis, and
other tissue cyst-forming coccidian of human and animals.
pp1-56. In: Parasitic protozoa (Kreier, P.J. ed), vol. 6, 2nd
ed., Academic Press, Inc., San Diego, California.
Inoue, M. (1997) Acute toxoplasmosis in squirrel monkeys. J.
Vet. Med. Sci. 59:593-595.
Ruch, T.C. (1959). pp.297-299, 313-318, 423-424. In:
Diseases of laboratory primates. W.B. Saunders Co.,
Philadelphia.
Cunningham, A.A., Buxton, D. and Thomson, K.M. (1992) An
epidemic of toxoplasmosis in a captive colony of squirrel
monkeys (Saimiri sciureus). J. Comp. Pathol. 107:207-219.
Furuta, T., Une, Y., Omura, M., Matsutani, N., Nomura, Y.,
Kikuchi, T., Hattori, S. and Yoshikawa, Y. (2001) Horizontal
transmission of Toxoplasma gondii in squirrel monkeys (Saimiri
sciureus). Exp. Anim. 50:299-306.
Grover, M.C., Thulliez, P., Remington, J.S. and Boothroyd,
J.C. (1990) Rapid prenatal diagnosis of congenital Toxoplasma
infection by using polymerase chain reaction and amniotic
fluid. J. Clin. Microbiol. 28:2297-2301.
Dupouy-Camet, J., de Souza, S.L., Maslo, C., Paugam, A.,
Saimot, A.G., Benarous, R., Tourte-Schaefer, C. and Derouin,
F. (1993) Detection of Toxoplasma gondii in venous blood from
AIDS patients by polymerase chain reaction. J. Clin. Microbiol.
31:1866-1869.
Ho-Yen, D.O., Joss, A.W.L., Balflour, A.H., Smyth, E.T.M.,
Baird, D. and Chatterton, J.M.W. (1992) Use of the polymerase
chain reaction to detect Toxoplasma gondii in human blood
samples. J. Clin. Pathol. 45:910-913.
Johnson, J.D., Butcher, P.D., Savva, D. and Holliman, R.E.
(1993) Application of the polymerase chain reaction to the
diagnosis of human toxoplasmosis. J. Infect. 26:147-158.
Cristina, N.H., Pelloux, C., Goulhot, J.P., Brion, P.,
Leclercq, P. and Ambrosis-Thomas, P. (1993) Detection of
Toxoplasma gondii in AIDS patients by the polymerase chain
reaction. Infection 21:150-153.
Farmley, S.F., Goebel, F.D. and Remington, J.S. (1992)
Detection of Toxoplasma gondii in cerebrospinal fluid from
AIDS patients by polymerase chain reaction. J. Clin. Microbiol.
30:3000-3002.
Hussein, A.H., Nagaty, I.M. and Fouad, M.A. (2002)
Evaluation of IgM-ELISA versus PCR in diagnosis of recent
Toxoplasma gondii infection. J Egypt Soc Parasitol. 32:639-46.
Specimen requirement: 0.5
ml whole blood in EDTA (purple top) or ACD (yellow top) tube,
or 1 ml cat feces, or 0.5 ml amniotic fluid, CSF or tissue,
shipped overnight at room temperature; or tissue shipped
frozen.
For specimen types other than those listed
here, please call to confirm specimen acceptability and
shipping instructions.
For all specimen types, if there will be a
delay in shipping, or during very warm weather, refrigerate
specimens until shipped and ship with a cold pack unless more
stringent shipping requirements are specified. Frozen
specimens should be shipped so as to remain frozen in transit.
See shipping instructions for
more information.
Turnaround time: 2 business
days
Methodology: Qualitative
polymerase chain reaction
Normal range: Nondetected