Intraocular production of Toxoplasma gondii-specific antibody in cats has been estimated by comparing the ratio of T gondii-specific antibody in aqueous humor and serum with the ratio of total immunoglobulins in serum and aqueous humor (Goldmann-Witmer coefficient; aqueous antibody coefficient; C value). It has been proposed that in human beings, comparison of the ratio of T gondii-specific antibody in aqueous humor and serum with the ratio of antibodies against a nonocular pathogen in serum and aqueous humor is more accurate than methods using total immunoglobulin quantification. We developed an ELISA for detection of calicivirus-specific antibodies in the serum and aqueous humor of cats. By evaluating calicivirus-specific antibody concentrations in the aqueous humor of healthy and diseased cats, calicivirus was assessed as a nonintraocular pathogen. The ratio of T gondii-specific antibodies in the aqueous humor and serum and the ratio of calicivirus-specific antibodies in serum and aqueous humor were evaluated as a means of estimating intraocular T gondii-specific antibody production. A field strain of feline calicivirus was isolated, cultured, and purified. A calicivirus-specific IgG ELISA was developed for detection of feline calicivirus-specific IgG in serum and aqueous humor. Calicivirus-specific IgG was measured in the serum and aqueous humor from 3 groups of control cats. Results suggested that calicivirus is a nonintraocular pathogen in cats and that calicivirus IgG detected in aqueous humor is attributable to leakage across a damaged blood-ocular barrier. Intraocular production of T gondii-specific antibodies was estimated, using 2 formulas. The C value was calculated by multiplying the ratio of T gondii-specific IgM or IgG in aqueous humor and serum by the ratio of total immunoglobulins (using the corresponding IgM or IgG class) in serum and aqueous humor. The Ctc value (Toxoplasma-calicivirus Goldmann-Witmer coefficient) was calculated by multiplying the ratio of T gondii-specific IgM or IgG in aqueous humor and serum by the ratio of calicivirus-specific IgG in serum and aqueous humor. Serum and aqueous humor samples were obtained from 41 client-owned cats with uveitis, and T gondii-specific C values and Ctc values were calculated. Toxoplasma gondii-specific IgM or IgG C values of 10 or greater or T gondii-specific IgM or IgG Ctc values of 1 or greater were considered to be suggestive of intraocular T gondii-specific antibody production. Of the 41 cats, 20 (48.7%) had evidence of intraocular production of T gondii-specific antibody on the basis of either an IgM or IgG C value of 10 or greater. A Ctc value could not be calculated in 3 cats because calicivirus-specific IgG was not present in aqueous humor. Of the 38 cats for which Ctc values could be calculated, 25 (65.8%) had evidence of intraocular production of T gondii-specific antibody on the basis of either an IgM or IgG Ctc value of 1 or greater. The C values and Ctc values were in agreement for 75.9% of IgM containing samples and 75% of IgG containing samples. Sensitivity, specificity, predictive value of a positive test result, and predictive value of a negative test result for an IgM or IgG C value, when compared with the corresponding IgM or IgG Ctc value were determined. The results indicate that use of the C value for estimation of intraocular T gondii-specific antibody production will result in 28.6 (IgM) to 50% IgG) false-negative results and 12.5% (IgM and IgG) false-positive results, when compared with the Ctc value.

Toxoplasma gondii-specific IgA, IgM, and IgG were measured by ELISA in the serum and aqueous humor of 29 client-owned cats with indigenous aviates and 7 specific-pathogen-free cats tested sequentially for 20 weeks after inoculation with T. gondii. Local antibody production in aqueous humor was estimated by multiplying the aqueous humor-to-serum T gondii-specific antibody ratio by the serum-to-aqueous humor total IgG (C value) or IgG (C value) ratio. Evidence for local production of antibody in aqueous humor was defined as C value greater than 8 or CTC value greater than 1. Toxoplasma gondii-specific IgM CTC values, IgG CTC values, or IgA CTC values greater than 1 were detected in the aqueous humor of 18 of 29 (62.1%) client-owned cats with endogenous uveitis; 2 cats had IgA CTC values greater than 1 without detectable IgM or IgG in aqueous humor. Toxoplasma gondii-specific IgM was not detected in the aqueous humor of experimentally inoculated cats before or after inoculation. Immunoglobulin G C values greater than 8 were detected in all 7 experimentally inoculated cats and ranged from 10.4 to 145.5. Immunoglobulin G C values greater than 8 were first detected 4 to 8 weeks after T gondii inoculation and were undetectable by week 16 after inoculation. Immunoglobulin A C values greater than 8 were detected in 4 of 7 cats and ranged from 12.7 to 264.3. Immunoglobulin A C values greater than 8 were first detected 4 to 8 weeks after inoculation, and were detected in 2 cats during week 20 after inoculation. It was concluded that some cats infected with T gondii develop detectable concentrations of T gondii-specific IgA in aqueous humor.

Persistence of the vaccine RH strain of Toxoplasma gondii was studied by bioassay and histologically in 14 pigs. Pigs were euthanatized 2, 4, 7, 8, 14, 15, 21, 29, 36, 42, 52, 57, and 76 days after IM inoculation with 100,000 T gondii tachyzoites. Viable T gondii tachyzoites derived from the RH strain were isolated by bioassay in mice inoculated with tissues of pigs euthanatized up to 14 days after vaccination. Except for fever, pigs vaccinated IM with the RH strain remained clinically normal. Two other pigs inoculated IV with 100,000 T gondii tachyzoites of the RH strain became ill, and 1 pig was comatose by 4 days after inoculation. These findings indicate that route of inoculation may influence the response of pigs to T gondii. To evaluate protective immunity in pigs vaccinated with the RH strain, 16 age-matched pigs were allotted to 4 groups (A-D) of 4 pigs each. Eight pigs (groups A and C) were vaccinated IM with 100,000 RH strain tachyzoites and 8 pigs (groups B and D) were nonvaccinated controls. Pigs of groups A and C were challenge-inoculated orally with a lethal dose of T gondii oocysts (100,000 oocysts) 81 days after vaccination, pigs of groups B and D were inoculated similarly 220 days after vaccination. The concentration of T gondii at 3 days after challenge inoculation of pigs vaccinated 81 days earlier was reduced 100,000-fold in mesenteric lymph nodes, compared with that in a nonvaccinated pig euthanatized at 3 days after challenge inoculation. Another nonvaccinated pig became comatose and had to be euthanatized at 7 days after challenge inoculation, numerous tachyzoites were in its mesenteric lymph nodes, intestines, and liver. The vaccinated pigs generally remained clinically after challenge inoculation with oocysts. Toxoplasma gondii was not isolated by bioassays from tissues of 5 of 8 vaccinated pigs, but was recovered from all nonvaccinated pigs. Results indicate that protective immunity persisted in pigs for at least 7 months after vaccination with the nonpersistent RH strain of T gondii.

During the hunting season of 1992, 322 black bears from Pennsylvania were examined for Toxoplasma gondii- and Trichinella spp-induced infections. Toxoplasma gondii antibodies were found in 79.8% of 322 bears--titer < 1:25 in 65 (20.2%), 1:25 in 18 (5.6%), 1:50 in 11 (34.5%) and 1:500 in 128 (38.7%) bears--by use of the modified agglutination test. Muscle tissues from 89 of these bears were bioassayed for T gondii parasites. Muscles from 64 bears, including heart from 1 bear, and heart alone from another bear, were digested in pepsin, and the digested samples were bioassayed in mice. Toxoplasma gondii was isolated from 5 bears; from the heart of 1, heart and skeletal muscles of 1, and skeletal muscles of 3. The T gondii antibody titers for the 5 bears with detectable T gondii were: greater than or equal to 1:25 in all 5 bears by use of the modified agglutination test; < 1:10 (3 bears, considered Toxoplasma-negative), 1:20 and 1:320 by use of the Sabin-Feldman dye test; < 1:64 (3 bears, considered Toxoplasma-negative), 1:128, 1:512 by use of the indirect hemagglutination test, and < 1:16 (2 bears, considered Toxoplasma-negative), 1:32, 1:64, and 1:512 by use of the latex agglutination test. Toxoplasma gondii was not isolated from feces of 5 cats fed muscles from the remaining 25 bears with T gondii antibody titer < 1:25. Tissue cysts of the 4 T gondii isolates from bears were rendered noninfective by freezing at -13 C. Antibodies against Trichinella spp were found in 6 (1.8%) of 319 bear sera; Trichinella spp larvae were detected in muscle digests of 2 of 63 bears, and in histologic sections of muscles from 3 of 162 bears. Genetic typing indicated that the 2 Trichinella isolates from bears were a sylvatic genotype and were not the species found in domestic pigs.

Four-week-old chickens were inoculated orally with 1,000 or 100,000 oocysts of the ME-49 or GT-1 strain of Toxoplasma gondii, and their antibody responses were measured, using the direct modified agglutination test, latex agglutination test, indirect hemagglutination test, ELISA, and the Sabin-Feldman dye test. Antibodies against T gondii were detected by use of the modified agglutination test and ELISA within 2 weeks of oocyst inoculation, and antibodies persisted until termination of the study by postinoculation day 68. The latex agglutination test was insensitive in detecting T gondii antibodies, and antibodies were not detected by use of the dye and indirect hemagglutination tests. Of tissues bioassayed in mice for tissue cysts by pepsin digestion of individual organs of chickens on postinoculation day 68, tissue cysts were found in the brain of all 5, heart of 3, and leg muscles of 2, but not in the liver and breast muscles. None of the birds developed clinical toxoplasmosis.

Kittens are the principal disseminators of Toxoplasma gondii. They can shed > 10(8) oocysts in the feces after initial infection with bradyzoites in tissue cysts. Thereafter, most kittens develop protective immunity and do not shed oocysts again if they are reinfected. Bradyzoites of a T gondii mutant, designated T-263, were used to vaccinate kittens. Their use did not result in oocyst shedding, but successfully prevented 84% (31/37) of the kittens from shedding oocysts when challenge exposed with a normal isolate of T gondii. Vaccination of outdoor-roaming cats and kittens would be a useful public health measure to prevent transmission of toxoplasmosis near homes, on farms, and in zoos. It is anticipated that several years will be required for a lyophilized bradyzoite vaccine to be ready for licensing and possible commercial availability.

Seventeen sows were fed 1,000 Toxoplasma gondii oocysts of isolates GT-1 or PT-1 at 32 to 92 days of gestation, and the products of conception were examined for T gondii antibodies and parasites. Twelve of these sows were euthanatized near term between 21 and 62 days after being fed T gondii; fetal body fluids or fetal sera were examined for agglutinating T gondii antibodies, and tissues were bioassayed in mice for T gondii parasites. Six sows produced pigs that had been transplacentally infected with T gondii; one of them aborted a T gondii-infected fetus 17 days after ingesting oocytes. Agglutinating antibodies were detected in fetuses infected in utero, but transplacental transfer of T gondii antibodies was not observed in noninfected fetuses. Transcolostrally acquired T gondii antibodies disappeared by 3 months of age. Diagnosis of transplacental toxoplasmosis was confirmed on the basis of detection of T gondii organisms in fetal tissues by use of histologic examination and bioassay in mice. In conclusion, finding of T gondii antibodies in body fluids could serve as a rapid screening test for transplacental T gondii infection in pigs.

An ELISA was developed to detect circulating antigens of Toxoplasma gondii in the serum of cats. For the experiment, toxoplasmosis was induced in a group of cats by oral administration of bradyzoites. An ELISA that detects anti-Toxoplasma IgG, an ELISA to detect circulating antigens, and fecal examinations were performed on samples from each cat for 1 year after inoculation. When coupled with IgG-class antibody measurement, antigen detection can aid in the diagnosis of some cases of subclinical feline toxoplasmosis.

Toxoplasma gondii, goats, prevention of abortion and neonatal death by vaccination with nonpathogenic coccidium Hammondia hammondi

Toxoplasma gondii is a major neglected parasitic infection occurring in settings of extreme poverty in Africa. Apart from causing reproductive failure in animals it is also a significant zoonotic concern. The objective of this study was to determine the seroprevalence and associated risk factors of T. gondii infection in cats, chickens, goats, sheep and pigs in the southeast of South Africa, of which little is known. Sera was obtained from 601 domestic animals including 109 cats, 137 chickens, 128 goats, 121 sheep and 106 pigs managed under different production systems in different agro-ecological regions and evaluated by the Toxoreagent, a latex agglutination test for T. gondii antibody detection. Household-level and animal-level data were collected by interviewing animal owners and/or herders using a closed-ended questionnaire. The study revealed an overall farm seroprevalence of 83.33% (125/150 farms) with the highest rate of infection for the parasite found in sheep with 64.46% (78/121), followed by goats with 53.91% (69/128), pigs with 33.96% (36/106), cats with 32.11% (35/109 cats) and chickens with 33.58% (46/137). The risk factors that were found to be statistically significant (p < 0.05) to different species of seropositivites were age, location, climate, animal production system, rodent control, seropositive cat, cat-feed access and cat faecal disposal. The relatively high seroprevalence of T. gondii detected in this region suggests that domestic animals may pose a substantial public health risk through the consumption of T. gondii-infected raw meat as well as via contact with cat faeces.