Toxoplasmosis and Other Systemic Protozoal Infections

Chapter 21 Toxoplasmosis and Other Systemic Protozoal Infections



The protozoa that infect dogs and cats can be classified broadly into those that disseminate and cause systemic disease and those that primarily live in the intestinal tract. This chapter describes toxoplasmosis, the most important systemic protozoal infectious disease in North America, and other emerging systemic protozoal infections—neosporosis, hepatozoonosis, and leishmaniasis. These and other systemic protozoal infections are summarized in Table 21-1, including trypanosomiasis, babesiosis, cytauxzoonosis, encephalitozoonosis, acanthamebiasis, and pneumocystosis.



Protozoa that parasitize erythrocytes, such as Babesia spp. and Cytauxzoon felis, are discussed in Chapter 22. Enteric protozoal infections (coccidiosis, giardiasis, tritrichomoniasis, amebiasis, and balantidiasis) are discussed in Chapter 69.



TOXOPLASMOSIS





Routes of Transmission


Warm-blooded vertebrates can be infected by ingestion of any of the three life stages of the parasite (see the next section) or transplacentally.






Stages of Infection


The three stages of Toxoplasma infection are (1) intestinal replication (cats only), (2) acute dissemination and intracellular replication, and (3) chronic tissue encystment.






Clinical Signs


Clinical toxoplasmosis is recognized more frequently in cats than in dogs, but the spectrum of signs is similar for both species. Clinical signs depend on the location and extent of tissue damage that results from extraintestinal dissemination and rapid intracellular replication of tachyzoites. The most commonly affected organs are lung, eyes, liver, and pancreas, as well as CNS and skeletal muscle. Organ-specific clinical signs are usually accompanied by anorexia, depression, and fever (often >104°F and unresponsive to antibiotics).













Laboratory and Radiographic Findings


Abnormalities found on routine diagnostics are varied and nonspecific.






Diagnosis


The diagnosis of clinical toxoplasmosis is usually based on the combination of clinical findings and serologic and PCR testing of blood, CSF, and aqueous humor. PCR assays and serologic tests for immunoglobulin M and G (IgM and IgG) are available to the practicing veterinarian through the Veterinary Diagnostic Laboratory (College of Veterinary Medicine, Colorado State University, Fort Collins, CO 80523) and other reference labs.





Serology


Enzyme-linked immunosorbent assay (ELISA) methods are generally most reliable for determining Toxoplasma-specific antibody titers. Positive IgG and IgM antibody titers document previous or current infection. The IgM titer reflects the early immune response and has the best correlation with clinically active toxoplasmosis.





Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Toxoplasmosis and Other Systemic Protozoal Infections

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