Page 1551 - Small Animal Internal Medicine, 6th Edition

CHAPTER 98 Polysystemic Protozoal Infections 1523

Kittens infected transplacentally or lactationally com- Some cats with clinical toxoplasmosis will have reached
monly develop ocular disease. Immune complex formation their maximal IgG titer or have undergone antibody class
VetBooks.ir and deposition in tissues and delayed hypersensitivity reac- shift from IgM to IgG by the time they are serologically
evaluated, so the failure to document an increasing IgG titer
tions may be involved in chronic, sublethal clinical toxoplas-
mosis. Although chronic tissue infection and immune
clinical toxoplasmosis. Because some healthy cats have
complex formation are common, there was no association or a positive IgM titer does not exclude the diagnosis of
between T. gondii antibodies and chronic kidney disease in extremely high serum antibody titers and some clinically ill
one study (Hsu et al., 2011). None of the anti-Toxoplasma cats have low serum antibody titers, the magnitude of titer
drugs totally clear the body of the organism, so recurrence is relatively unimportant in the clinical diagnosis of toxo-
of disease may occur in some cats, and serum IgG titers plasmosis. Because the organism cannot be cleared from the
rarely become negative. body, most cats will be antibody positive for life, so repeating
serum antibody titers after the clinical disease has resolved
Diagnosis is not necessary.
Cats with clinical toxoplasmosis can have a variety of clini- The combination of aqueous humor or CSF T. gondii–
copathologic and radiographic abnormalities, but none specific antibody detection and T. gondii DNA amplification
documents the disease. Nonregenerative anemia, neutro- by PCR is the most accurate way to diagnose ocular or CNS
philic leukocytosis, lymphocytosis, monocytosis, neutro- toxoplasmosis (www.dlab.colostate.edu; Diagnostic Labora-
penia, eosinophilia, proteinuria, and bilirubinuria, as well tory, College of Veterinary Medicine and Biomedical Sci-
as increases in serum protein and bilirubin concentrations, ences, Colorado State University, Fort Collins). For example,
creatinine kinase, alanine aminotransferase, alkaline phos- in one study of six cats with uveitis, five had T. gondii DNA
phatase, and lipase activities occur in some cats. Pulmonary in blood or aqueous humor but were seronegative for T.
toxoplasmosis most commonly causes diffuse interstitial to gondii antibodies (Powell et al., 2010). Whereas T. gondii–
alveolar patterns or pleural effusion. Mass lesions may be specific IgA, IgG, and T. gondii DNA can be detected in
detected on computed tomography or magnetic resonance aqueous humor and CSF of both normal and clinically ill
imaging examinations. CSF protein concentrations and cell cats, T. gondii–specific IgM has only been detected in the
counts are often higher than normal. The predominant white aqueous humor or CSF of clinically ill cats and therefore may
blood cells in CSF are small mononuclear cells, but neutro- be the best indicator of clinical disease. Because T. gondii
phils are also commonly found. DNA can be amplified from the blood of healthy cats, posi-
The antemortem definitive diagnosis of feline toxoplas- tive PCR results do not always correlate to clinical disease
mosis can be made if the organism is demonstrated; however, (Burney et al., 1999).
this is uncommon, particularly in association with sublethal
disease. Bradyzoites or tachyzoites are rarely detected in Treatment
tissues, effusions, bronchoalveolar lavage fluids, aqueous Supportive care should be instituted as needed. Clindamy-
humor, or CSF. Visualization of 10 × 12 µm oocysts in feces cin hydrochloride (10-12 mg/kg PO q12h) administered for
in cats with diarrhea suggests toxoplasmosis but is not defin- 4 weeks has been used most frequently by the author for
itive because Besnoitia and Hammondia infections of cats the treatment of clinical feline toxoplasmosis. Azithromy-
produce morphologically similar oocysts. cin (10.0 mg/kg PO q24h) has been used successfully in a
Toxoplasma gondii–specific antibodies (IgM, IgG, IgA), limited number of cats, but the optimal duration of therapy is
antigens, and immune complexes can be detected in the unknown. Ponazuril was apparently successful for the treat-
serum of normal cats, as well as in those with clinical signs ment of T. gondii infection in a dog and also has been shown
of disease, so antemortem diagnosis of clinical toxoplasmo- to have anti-T. gondii effects in a mouse model (Mitchell
sis is impossible on the basis of these tests alone. Of the et al., 2004). Ponazuril is known to be safe in cats for the
serum tests, IgM correlates the best with clinical feline toxo- treatment of Isospora spp. infection and should be studied
plasmosis because this antibody class is rarely detected in further for use in affected cats. Trimethoprim-sulfonamide
serum of healthy cats. The antemortem diagnosis of clinical combination has been used at 15 mg/kg PO q12h for 4
toxoplasmosis can be tentatively based on the combination weeks in some cats with toxoplasmosis but is not tolerated
of the following: by many cats. Pyrimethamine combined with sulfa drugs
is effective for the treatment of human toxoplasmosis but
• Demonstration of antibodies in serum, which documents commonly results in vomiting or inappetance and can cause
exposure to T. gondii anemia in cats. Cats with systemic clinical signs of toxoplas-
• Demonstration of an IgM titer above 1 : 64 or a fourfold mosis, such as fever or muscle pain combined with uveitis,
or greater increase in IgG titer, which suggests recent or should be treated with anti-Toxoplasma drugs in combina-
active infection tion with topical, oral, or parenteral corticosteroids to avoid
• Clinical signs of disease referable to toxoplasmosis secondary lens luxations and glaucoma. Toxoplasma gondii–
• Exclusion of other common causes for the clinical seropositive cats with uveitis that are otherwise normal
syndrome can be treated with topical glucocorticoids alone unless
• Positive response to appropriate treatment the uveitis is recurrent or persistent. In these situations,