Toxoplasma gondii Antibodies in Cats: Detection by Indirect Hemagglutination and Indirect Fluorescent Antibody Tests

Abstract

The distribution of Toxoplasma gondii infection in cats is usually reported as specific antibody titers detected by the Sabin-Feldman dye test, indirect hemagglutination (IHA) test, or indirect fluorescent antibody (IFA) test. The dye test has been compared to the IHA (Jacobs and Lunde, 1957, Journal of Parasitology 43: 308314) and IFA tests (Walton et al., 1966, American Journal of Tropical Medicine and Hygiene 15: 149-152) in humans and to the IFA test in cats (Claus et al., 1977, Journal of Parasitology 63: 266). The IHA and IFA (using anti-cat serum) tests also have been compared in cats (Behymer et al., 1973, Journal of the American Veterinary Medical Association 162: 959-963). This report compares the detection of T. gondii antibodies by the IHA and IFA (using either anticat whole serum or anti-cat IgG) tests in 324 cats from Beirut, Lebanon. From September 1980 through July 1983 (35 mo) 324 domestic stray and owned cats in Beirut, Lebanon were tested for antibodies to T. gondii. The data from the 2 groups of cats were combined because the prevalence of cats with antibody titers >1:64 was not significantly different between stray and owned adult cats in Beirut (Deeb et al., Journal of Tropical Medicine and Hygiene, in press). A commercially available kit (Wampole Laboratories, Div. of Carter-Wallace Inc., Cranbury, New Jersey 08512) was used for the IHA test. Sera were screened at a dilution of 1:64 and titrated using two-fold serial dilutions to a dilution of 1:2,048. Sera were absorbed with unsensitized, stabilized sheep erythrocytes to remove nonspecific agglutinins. The IFA test was modified from Kagan and Norman (1976. In Manual of clinical immunology, pp. 382-385) and performed using lyophilized T. gondii organisms, immunofluorescence test slides, and buffered solutions obtained from bio-Merieux, Marcy l'Etoile, 69260 Charbonnieres les Bains, France. Two-fold serial dilutions of sera from 1:64 to 1:2,048 were made using phosphate-buffered saline (PBS) at pH 7.2. A 1:32 dilution of fluorescein-labeled goat anticat IgG or anti-cat whole serum, containing 0.2% Evans blue (Cappel Laboratories, Div. of Biological Corp. of America, Cochranville, Pennsylvania 19330) was added. Both of the fluorescein-labeled products were filtered through a 0.45 ,um membrane filter (Millipore Corp., U.S.A.). The fluorescein-labeled products measured the same titer when used on a known anti-toxoplasma cat serum control. Slides were examined with a fluorescent microscope, using known positive and negative cat sera as controls. A positive reaction consisted of green fluorescence around the entire periphery of the parasite; a negative reaction was polar but not circumferential fluores-