Page 1550 - Small Animal Internal Medicine, 6th Edition

1522 PART XIV Infectious Diseases

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FIG 98.5
Unstained Toxoplasma gondii unsporulated oocysts. The
oocysts are 10 × 12 µm.

(Fig. 98.5). Results of a research study confirm that the T.
gondii oocyst-shedding prepatent period is stage-dependent
(ingestion of bradyzoites has a shorted prepatent period than FIG 98.6
ingestion of sporozoites) and not dose-dependent (Dubey Punctate chorioretinitis caused by Toxoplasma gondii in an
et al., 2006). In addition, transmission of T. gondii is most experimentally inoculated cat.
efficient when cats consume tissue cysts (carnivorism) and
when intermediate hosts consume oocysts (fecal-oral trans-
mission). Toxoplasma gondii infection of rodents changes the tissues are commonly involved. Kittens infected by the trans-
behavior of the prey species, making it less averse to cats, placental or transmammary routes develop the most severe
potentially increasing the likelihood the definitive host signs of extraintestinal toxoplasmosis and generally die of
(felid) will become infected and potentiate the sexual phase pulmonary or hepatic disease. Common clinical findings in
of the organism (Vyas et al., 2007). A number of studies have cats with disseminated toxoplasmosis include depression,
now evaluated whether T. gondii infection is associated with anorexia, and fever followed by hypothermia, peritoneal
behavioral abnormalities in people with mixed results (see effusion, icterus, and dyspnea.
Chapter 99). In one study of clinically ill cats in the United If a host with chronic toxoplasmosis is immunosup-
States, T. gondii antibodies were detected in 31.6% of the pressed, bradyzoites in tissue cysts can replicate rapidly
12,628 cats tested (Vollaire et al., 2005) so cats are commonly and disseminate again as tachyzoites; this is common in
exposed to the agent, likely from predation in most. people with acquired immunodeficiency syndrome (AIDS).
Disseminated toxoplasmosis has been documented in cats
Clinical Features concurrently infected with feline leukemia, feline immuno-
Approximately 10% to 20% of experimentally inoculated cats deficiency, or feline infectious peritonitis viruses, as well as
develop self-limiting, small-bowel diarrhea for 1 to 2 weeks after cyclosporine administration for skin disease or after
after primary oral inoculation with T. gondii tissue cysts; this renal transplantation (Barrs et al; 2006). The acute respira-
is presumed to be from enteroepithelial replication of the tory distress syndrome was recently documented in a cat
organism. However, detection of T. gondii oocysts in feces is with disseminated toxoplasmosis (Evans et al., 2017).
rarely reported in studies of naturally exposed cats with or Sublethal, chronic toxoplasmosis occurs in some cats.
without diarrhea because of the short shedding period. For Toxoplasma gondii infection should be on the list of differ-
example, in a study in Germany the oocyst-shedding rate ential diagnoses for cats with anterior or posterior uveitis,
was estimated at 0.8% in 8640 cats (Barutzki and Schaper, cutaneous lesions, fever, muscle hyperesthesia, myocarditis
2011). Toxoplasma gondii enteroepithelial stages were found with arrhythmias, weight loss, anorexia, seizures, ataxia,
in intestinal tissues from two cats with inflammatory bowel icterus, diarrhea, or pancreatitis (Fig. 98.6). Cutaneous toxo-
disease. Positive response to anti-Toxoplasma drugs in these plasmosis is characterised by hyperemic nodules that may or
two cats suggests that toxoplasmosis may occasionally induce may not be ulcerated. On the basis of results of T. gondii–
inflammatory bowel disease. specific aqueous humor antibody and PCR studies, toxoplas-
Fatal extraintestinal toxoplasmosis can develop from mosis appears to be a common infectious cause of uveitis in
overwhelming intracellular replication of tachyzoites after cats. Distal polyneuropathies can occur in dogs or cats (Mari
primary infection; hepatic, pulmonary, CNS, and pancreatic et al., 2016).