Prevalence of Toxoplasma gondii infection in man and animals in Guangdong, People's Republic of China
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To determine the seroprevalence of Toxoplasma gondii (T. gondii) infection in dogs and cats in Zhenjiang City, Jiangsu Province, Eastern China, and to evaluate the main associated risk factors relating to exposure to T. gondii in this region. Sera from 160 dogs and 116 cats from Zhenjiang City were tested for anti-T. gondii antibodies using ELISA. The seropositivity by area of activity, sex and age was analyzed. Overall, 21 dogs (13.1%) and 24 cats (20.7%) had antibodies to T. gondii. The infection rate in stray dogs (38.7%) and cats (28.6%) was significantly higher (P<0.05) than in household dogs (6.9%) and cats (18.2%). The seroprevalence in male dogs (14.8%) and cats (21.05%) were slightly higher than their female counterparts (11.4% in dogs and 20.0% in cats), but were not significantly differenent (P>0.05). A high proportion of dogs at 3 to 6 years of age were positive to T. gondii (20.0%) while cats with relatively high seropositivity rates were at 0 to 1 year of age (33.3%). The prevalence of T. gondii infection in dogs and cats in Zhenjiang City was high, which is probably the main source of T. gondii infection in this area.
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The prevalence of Toxoplasma gondii antibodies in 80 domestic cats was studied in the city of Colima, Mexico, using an indirect IgG-ELISA. Antibodies were found in 28.8% of the cats, with significantly higher (P = 0.029) prevalence in southern and central zones (33.8%) than the northern zone (6.6%). Prevalence among cats fed with homemade food was higher than those eating commercial pellets (40.6% [vs.] 20.8%; P = 0.055). Overall, the prevalence of T. gondii antibodies in the cats of Colima was lower than in many other countries.
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Serum and aqueous humor samples, collected from 14 clinically normal cats and 96 cats with clinical evidence of intraocular inflammation, were assayed with ELISA for Toxoplasma gondii-specific immunoglobulin M (IgM), T gondii-specific IgG, T gondii-specific antigens, total IgG, and total IgM. Additionally, serum was assayed with ELISA for feline leukemia virus p27 antigen and antibodies against the feline immunodeficiency virus as well as with an immunofluorescent antibody assay for antibodies against feline coronaviruses. Calculation of the Goldmann-Witmer coefficient (C-value) for the T gondii-specific antibodies detected in aqueous humor established the likelihood of local antibody production. Serologic evidence of present or prior infection by an infectious agent was found in 81.9% of the clinically affected cats from which serologic results were available (77/94 cats). Seropositive results for toxoplasmosis were found in 74.0% of the clinically affected cats. Anterior segment inflammation was found in 93.1% (81/87 cats from which information was available) of the clinically affected cats, most of which were older males. Toxoplasma gondii-specific antibodies were not detected in the aqueous humor of 6 seropositive, clinically normal cats. The C-values for aqueous T gondii antibodies were greater than 1 in 44.8% of the cats and greater than 8 in 24.0% of the cats. Response to treatment with clindamycin HCl was positive in 15/20 (75%) of the T gondii-seropositive, clinically affected cats treated with this drug. In 13/15 (86.7%) T gondii-seropositive, clinically affected cats having a C-value greater than 1, response to treatment with clindamycin HCl was positive.(ABSTRACT TRUNCATED AT 250 WORDS)
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Abstract Toxoplasma gondii is a widespread parasitic pathogen that infect humans and all warm-blooded animals, causing abortion and stillbirth in pregnant women and animals, as well as life threatening toxoplasmosis in immune compromised individuals. Felines are the only definitive hosts of Toxoplasma and oocysts shed by infected felines are the major source of infection for humans and other animals. Given the critical role of felines for T. gondii transmission, control of feline toxoplasmosis has significant impacts on reducing the overall prevalence of animal and human toxoplasmosis. However, reliable diagnosis of feline toxoplasmosis is still challenging. In this study, we found that the putative micronemal protein 17A (MIC17A) that was abundantly expressed in Toxoplasma merozoites is a good diagnostic marker for serological diagnosis of Toxoplasma infection in felines. T. gondii encodes four paralogs of MIC17A in total and the expression of three of them is drastically upregulated in merozoites than in tachyzoites. In contrast, when proteins like GRA1 and MIC3 that are more abundantly expressed in tachyzoites than in merozoites were used as diagnostic antigens to test feline toxoplasmosis, they reacted with Toxoplasma specific IgG antibodies poorly. Taken together, these results suggest that merozoite antigens are better suited for the diagnosis of feline toxoplasmosis than antigens that are highly expressed at tachyzoite or bradyzoite stages.
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Immunity to Toxoplasma gondii, as measured by oocyst shedding, was studied in cats. In 3 trials, 12 3-mo-old T. gondii-free cats were fed tissue cysts of the ME-49 strain of T. gondii. All cats shed T. gondii oocysts for approximately 1 wk starting 3-5 days after ingesting tissue cysts. One cat became ill because of toxoplasmic pneumonia and was killed 17 days after inoculation. The remaining cats remained clinically normal. Approximately 3 mo after primary infection, these 11 cats (immune) and 11 age-matched or littermate uninfected cats (nonimmune) were challenged orally with tissue cysts of the ME-49 strain. In trials 1 and 3, 1 immune and 1 nonimmune cat were killed at 36 hr, 60 hr, 5 days, and 12 days after challenge and the development of T. gondii in intestines was studied histologically; in trial 2, cats were killed at 36 hr, 60 hr, and 5 days only. None of the "immune" cats shed oocysts after challenge. Asexual T. gondii types were found at 36 and 60 hr and at 5 days, indicating partial development of T. gondii in the intestine of immune cats. There were no significant differences in lymphocyte CD4+/CD8+ from spleen, popliteal, and mesenteric lymph nodes of immune cats compared to nonimmune cats.
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The tachyzoite-induced cycle of Toxoplasma gondii was studied in 46 cats. Tachyzoites of the M-7741 or Me-49 strain of T. gondii were administered orally to cats by pouring into the mouth or by stomach tube, or by intraintestinal inoculation. Ten weaned cats that had been inoculated with tachyzoites directly in the intestine were killed 1, 3, 6, 9, 12, 15, 18, or 25 days later, and their tissues were studied histologically and bioassayed in mice. Toxoplasma gondii was demonstrable in the blood of 8 cats and in other tissues of all these 10. Four out of five 1- to 8-day-old cats fed tachyzoites by stomach tube became infected with T. gondii, and 1 became ill because of toxoplasmosis. All 19 weaned cats fed tachyzoites (poured into the mouth) became infected, and 6 died of acute toxoplasmosis 9–15 days after being fed T. gondii. Six out of 12 weaned cats fed tachyzoites by stomach tube became infected but were asymptomatic. Overall, 12 out of 26 cats observed for 19 days or more shed oocysts with a prepatent period (pp) of 19 days or more, with the sole exception of 1 cat that shed oocysts with a pp of 5 days. Entero-epithelial stages of T. gondii were not found in any cat before oocysts were shed. Cats shed up to 360 million oocysts in a day, and oocysts were shed for 4–6 days.
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The article presents the data of immunogram studies in seropositive and seronegative for Toxoplasma gondii cats and the dependence of the absolute number of immunocompetent cells on their housing conditions. The blood from domestic and stray cats aged 3 to 5 years in which IgG to T. gondii was detected during a serological study was used in the study. During analyzes of the average values of seropositive (SP) cats it was detected that 10 animals (22%) had sufficiently high IgG titers of 3.24±0.835 (P≤0.05) and only 5 cats (11%) can be considered as animals that did not come into contact with the causative agent of toxoplasmosis. Neutrophils, as immunoregulatory cells, are among the first to encounter and become infected with Toxoplasma after the parasite crosses the intestinal epithelium. Determination of phagocytic activity of neutrophils showed that in the SP stray cats this indicator is 2 times lower than in the SP domestic cats and more than 4.0 times in the seronegative (SN) domestic cats. Analysis of the absolute content of lymphocytes and their T-subpopulation in the blood of different cats’ groups showed that in the SP stray cats, these indicators were lower. It is a proven fact that in order to control the adequate immune response in animals, it is extremely important not only the quantitative value of the immunoregulatory cells’ population, but also the ratio between them. The obtained results indicate that among homeless animals the seropositivity for toxoplasmosis is twice that of domestic cats. It was found that the SP domestic cats have a higher rate of T-suppressors and due to this IРI is 2.38±0.175. While the SP homeless cats have a larger T-helper subpopulation of lymphocytes and IРI is 4.13±0.506. In the SP domestic cats, the absolute content of B-lymphocytes was 0.616±0.038 and this indicator is the highest compared to other groups. There are also differences in the blood content of NK cells, namely in the homeless SP animals, it is higher than in the domestic cats. From this it should be noted that stray cats infected with T. gondii are mainly responsible for the widespread and constant pressure of infection in the region.
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Toxoplasma gondii oocysts are highly infective to intermediate hosts including humans, pigs, and mice, but are considered less infective for cats, the definitive host. To determine infectivity of T. gondii oocysts for cats, 20 2- to 3-mo-old T. gondii-free cats in groups of 4 were fed graded doses of oocysts estimated to have 1, 10, 100, 1,000, or 10,000 mouse infective oocysts of the VEG strain of T. gondii. Feces of cats were examined for at least 35 days after feeding oocysts. All cats were killed, necropsied, their sera were tested for T. gondii antibodies, and tissues were bioassayed in mice. Three of the 4 cats fed 10,000 oocysts, 3 of the 4 cats fed 1,000 oocysts, and 2 of the 4 cats each fed 100 oocysts shed 7.3-162 million T. gondii oocysts in their feces, with a prepatent period of 18-44 days. Based on bioassay and antibody production, all 4 cats fed 10,000 oocysts, 3 of 4 cats fed 1,000 oocysts, 2 of 4 cats fed 100 oocysts, and 0 of 8 cats fed 1 or 10 oocysts acquired T. gondii infection. Antibodies to T. gondii were detected by the modified agglutination test in all 9 bioassay-proven T. gondii-infected cats and in none of the 11 cats without demonstrable T. gondii. In a series of other experiments, the age of the cat at the time of oocyst feeding and the administration of corticosteroids were found to have no influence on the prepatent periods after ingestion of oocysts. A review of published and unpublished data indicated that the minimum prepatent period to shedding of oocysts after the ingestion of oocysts by cats is 18 days.
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Enzyme-linked immunosorbent assays for the detection of Toxoplasma gondii antigen-containing IgM immune complexes (T gondii-specific IgM-IC) and IgG immune complexes (T gondii-specific IgG-IC) in the serum of cats were developed. Serum from clinically ill, naturally infected cats; healthy, naturally infected cats; and healthy cats experimentally inoculated with T gondii was assayed. All combinations of T gondii-specific IgM, IgG, antigens, IgM-IC, and IgG-IC were detected in naturally infected and experimentally infected cats. Clinically ill cats and cats with ocular signs of toxoplasmosis were more likely than healthy cats to have T gondii-specific IC in serum. It was concluded that T gondii-specific IC form in the serum of cats, may play a role in clinical disease development, and affect the results of T gondii-specific IgM, IgG, and antigen serologic assays.
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