Sarcocystis capracanis and Toxoplasma gondii infections in range goats from Texas

Specimens of tongues, esophagi, diaphragms, or abdominal muscles of 115 range goats from San Angelo, Tex, were examined for Sarcocystis and Toxoplasma gondii infections. Sarcocystis spp zoites were found microscopically in pepsin digests of muscles of 60.8% goats and sarcocysts of S capracanis were found in histologic sections of 27.8% goats. Sarcocysts were more common in sections of tongue (19.1%) than in those of other muscles (9.9% to 10.7%). A dog fed Sarcocystis-infected tissues shed sporocysts in feces, whereas 2 cats fed the same tissues did not shed sporocysts. Toxoplasma gondii was neither seen in histologic sections of goat tissues nor found by bioassays in mice or cats. Mice inoculated with pepsin digests of muscles did not develop T gondii infection and 2 cats fed goat tissues did not shed oocysts. Also, antibody to T gondii was not found in serum samples from goats. The low prevalence of T gondii infection in range goats may be because of the relative absence of domestic cats on Texas ranges.     

Protective immunity to toxoplasmosis in pigs vaccinated with a nonpersistent strain of Toxoplasma gondii

The RH strain of Toxoplasma gondii is highly virulent; 1 infective organism is uniformly lethal for mice. Three pigs inoculated SC with 10(3) tachyzoites of the RH strain developed fever, but otherwise remained normal, and T gondii was not demonstrated in their tissues by bioassay into mice. To determine whether vaccination with the RH strain could induce protective immunity to oral challenge with T gondii oocysts, 12 pigs were divided into 3 groups (A, B, C) of 4 pigs each. Pigs in groups A and B were inoculated IM with 10(6) tachyzoites of the RH strain and 4 pigs in group C served as uninoculated controls. Except for fever, the pigs remained clinically normal after inoculation with the RH strain and T gondii was not found by bioassay in mice of tissues from 4 pigs euthanatized 64 days after inoculation. Pigs in groups B and C were challenge-inoculated orally with 10(4) (4 pigs) or 10(5) (4 pigs) T gondii oocysts 72 days after vaccination with the RH strain. The previously uninoculated pigs developed fever, anorexia, and diarrhea from 3 to 8 days after the oocyst challenge. One of the 2 pigs given 10(5) oocysts became moribund because of toxoplasmosis and was euthanatized 9 days after inoculation. Pigs vaccinated with the RH strain remained free of clinical signs after challenge with oocysts. Results of the bioassays indicated that fewer tissue cysts developed in the RH strain-vaccinated pigs than in the previously uninoculated control pigs.     

Effect of irradiation on the viability of Toxoplasma gondii cysts in tissues of mice and pigs

Muscles from tongue, heart, and limbs of 14 pigs inoculated orally with Toxoplasma gondii oocysts were irradiated with 10, 20, 25, and 30 krad of gamma (cesium-137 and cobalt-60) irradiation. Viability of T gondii cysts was assayed by feeding porcine muscles to T gondii-free cats and/or by inoculation of sediment from acid-pepsin digested porcine muscle into mice. Cats fed 500-g samples of muscles irradiated with up to 20 krad shed T gondii oocysts. Cats fed muscles irradiated with 25 or 30 krad did not shed oocysts. Mice were inoculated with 8 isolates of T gondii, and tissue cysts in their brains irradiated with up to 40 krad were infective to mice; however, there was a 10,000-fold reduction in the viability of organisms in tissue cysts irradiated with 40 krad, compared with that in nonirradiated cysts. At 50 krad of gamma irradiation, there were no detectable infective organisms in infected mouse brains.     

Persistence of encysted Toxoplasma gondii in tissues of pigs fed oocysts

Ten pigs were fed 100 to 10,000 Toxoplasma gondii oocysts. Two pigs died 7 and 11 days later, and 8 pigs were euthanatized at days 38, 38, 91, 126, 168, 169, 170, and 171. From the euthanatized pigs, portions of 15 organs digested in pepsin-HCl solution were inoculated into mice, as a bioassay for viable T gondii. Such organisms were isolated from the brain and heart of these 8 pigs, from the tongue of 7, from thigh muscles of 5, from the diaphragm of 4, from kidneys, liver, and small intestines of 2, and from salivary glands and eyes of 1 pig; but not from lungs, spleen, spinal cord, mesenteric and prescapular lymph nodes of any pig. Results indicate that T gondii can persist in edible tissues of living pigs for at least 171 days and that heart and brain may be the most suitable porcine tissues for epizootiologic surveys.     

Prevalence of Toxoplasma gondii in dogs from Colombia, South America and genetic characterization of T. gondii isolates

The prevalence of Toxoplasma gondii in 309 unwanted dogs from Bogotá, Colombia, South America was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT) and found in 52 (16.8%) of 309 dogs with titers of 1:20 in 20, 1:40 in six, 1:80 in 17, 1:160 in three, 1:320 in three, 1:1280 or higher in three. Some organs obtained after necropsy of dogs (hearts, tongues and brains, either separately or pooled) were used in bioassays carried out in mice (37 samples, of which 20 were assayed with separate organs and 17 were assayed with pooled organs), cats (pooled organs from six) and pooled organs of two dogs both in mice and cat. Mice receiving dog tissues were examined for T. gondii infection. Feces of cats that received dog tissues were examined for oocyst shedding. In total, T. gondii was isolated from tissues of 20 dogs (16 by bioassays in mice, 3 by bioassay in cats and 1 by bioassay in mice and cat). All infected mice from 7 of 17 isolates bioassayed in this host died of toxoplasmosis during primary infection. Only 10 of the 20 dogs whose tissues were bioassayed separately induced infections in mice. Interestingly, dog organs varied in their capacity to induce T. gondii infection in mice, hearts and tongues producing more positive results than the brain. The 20 T. gondii isolates obtained from seropositive dogs were PCR-RFLP genotyped using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, a new SAG2 and an apicoplast marker Apico. Ten genotypes were revealed. These genotypes are different from the three predominant Types I, II and III lineages that are widely spread in North America and Europe. A new allele denoted u-3 at PK1 locus was identified in three isolates. This result supports previous findings that T. gondii population is highly diverse in Colombia.     

Toxoplasma gondii cysts in placentas of experimentally infected sheep

To determine the presence of tissue cysts in ovine placentas, 6 ewes were inoculated orally with 10,000 Toxoplasma gondii oocysts at 60 days of gestation. The ewes were euthanatized and necropsied 21, 52, 56, 57, 57, and 62 days after T gondii inoculation, and placental cotyledons from each ewe were collected and homogenized. To distinguish between the presence of tachyzoites that are killed by acid pepsin solution and bradyzoites (from cysts) unaffected by this solution, a portion of each homogenate was inoculated into mice and another portion was inoculated into mice after digestion in acid pepsin solution. Toxoplasma gondii was isolated in 26 of 34 (76.4%) of mice inoculated with nondigested placentas of all 6 ewes and in 16 of 34 (47%) mice inoculated with digested placenta of 5 of 6 ewes. Seemingly, cysts do occur in placental tissue, but the digestion method was inferior, compared with the nondigestion method for recovery of T gondii from placenta.     

Prevalence of Toxoplasma gondii in cats from Colombia, South America and genetic characterization of T. gondii isolates

Cats are important in the epidemiology of Toxoplasma gondii infection because they are the only hosts that can excrete the environmentally-resistant oocysts. In the present study, prevalence of T. gondii was determined in serum, feces, and tissues of 170 unwanted cats from Colombia, South America. Antibodies to T. gondii were assayed by the modified agglutination test and found in 77 of 170 (45.2%) cats with titers of <1:5 in 93, 1:5 in eight, 1:10 in 17, 1:20 in 10, 1:40 in seven, 1:80 in four, 1:160 in eight, 1:320 in six, and 1:640 or higher in 17 cats. T. gondii oocysts were not found in feces of any cat as ascertained by bioassay in mice. Tissues (brain, heart, tongue) of 116 cats were bioassayed in mice or cats. T. gondii was isolated from tissues of 15 of the 42 cats with titers of 1:40 or higher and not from any of the 90 cats titers of 1:20 or lower. Of the 29 cats whose tissues were bioassayed individually, T. gondii was isolated from the tongues of nine, hearts of eight, and brains of five. Mice inoculated with tissues of 12 of 15 infected cats died of toxoplasmosis; with nine T. gondii isolates all infected mice died. Overall, 65 of 92 (70%) of T. gondii-infected mice died of toxoplasmosis. Genotyping of these 15 isolates using polymorphisms at the SAG1, SAG2, SAG3, BTUB, and GRA6 loci revealed that three isolates (TgCtCo1, 2, and 7) had Type I alleles and one isolate (TgCtCo8) had Type II allele at all five loci. Eleven isolates contained the combination of Type I and III alleles and were divided into three genotypes, with TgCtCo3,5,6,9,12,13 and 15 had alleles I, I, III, I and III, TgCtCo4,10,11 had alleles I, III, III, I and I, and TgCtCo14 had alleles I, III, III, III, and III, at loci SAG1, SAG2, SAG3, BTUB and GRA6, respectively. All infected mice from each group had identical genotype except one mouse infected with TgCtCo5 had a Type III allele at locus BTUB and a unique allele (u-1) at locus SAG1 indicating mixed infection for TgCtCo5, whereas the rest seven mice had a Type I alleles at both loci.     

High prevalence of Toxoplasma gondii in a commercial flock of chickens in Israel, and public health implications of free-range farming

Little is known of the prevalence of Toxoplasma gondii in commercially raised chickens. In the present study, the prevalence of T. gondii in 96 free-range chickens (Gallus domesticus) from a commercial farm in Israel was assessed. Blood, heart, and brain from each chicken were examined for T. gondii infection. Antibodies to T. gondii, assayed with the modified agglutination test (MAT > or = 1:5), were found in 45 of the 96 chickens. Hearts and brains of seropositive (MAT > or = 1:5) chickens were bioassayed in mice. Additionally, hearts and brains of 51 seronegative (MAT < 1:5) chickens were bioassayed in two T. gondii-free cats. T. gondii was isolated from 19 of the 45 (42.2%) seropositive chickens by bioassay in mice. Both the cats fed tissues pooled from seronegative chickens shed T. gondii oocysts. Tachyzoites and tissue cysts of all 21 isolates of T. gondii from chickens were avirulent for mice. Seventeen of the 19 isolates genotyped were found to be type II, and 2 were type III. Understanding of the sources of infection on such farms could be the key to the development of better prevention strategies.     

Comparative infectivity of oocysts and bradyzoites of Toxoplasma gondii for intermediate (mice) and definitive (cats) hosts

Tachyzoites, bradyzoites (in tissue cysts), and sporozoites (in oocysts) are the three infectious stages of Toxoplasma gondii. The prepatent period (time to shedding of oocysts after primary infection) varies with the stage of T. gondii ingested by the cat. The prepatent period (pp) after ingesting bradyzoites is short (3-10 days) while it is long (18 days or longer) after ingesting oocysts or tachyzoites. The conversion of bradyzoites to tachyzoites and tachyzoites to bradyzoites is biologically important in the life cycle of T. gondii and it has been proposed that the pp can be used to study stage conversion. In the present study, infectivity of oocysts and bradyzoites released from tissue cysts of a recent isolate of T. gondii, TgCkAr23, to cats and mice was compared. Ten-fold dilutions of oocysts or bradyzoites were administered orally to cats, and orally and subcutaneously to mice. Of the 29 cats each fed 1-10 million oocysts only one cat shed oocysts and the pp was 23 days; all cats remained asymptomatic. In contrast, all mice administered the same 10-fold dilutions of oocysts either orally or subcutaneously died of toxoplasmosis. The results confirm that infectivity of the oocysts to cats is lower than for mice and that oocysts are non-pathogenic for cats. Of the 41 cats each fed 1-1,000 free bradyzoites, 15 shed oocysts with a short pp of 4-9 days, and all remained asymptomatic. The infectivity of bradyzoites to mice by the oral route was approximately 100 times lower than that by the subcutaneous route. The results confirm the hypothesis that the pp in cats is stage and not dose dependent, and that transmission of T. gondii is most efficient when cats consume tissue cysts (carnivory) or when intermediate hosts consume oocysts (fecal-oral transmission).     

Attempeted transmission of feline coccidia from chronically infected queens to their kittens

Eight female, 12- to 34-month-old, specific-pathogen free cats were inoculated orally with Toxoplasma gondii cysts on day 0, then with Isospora felis and Isospora rivolta oocysts on day 39, and cysts of Hammondia hammondi on day 86 after inoculation with Toxoplasma. All cats shed oocysts of all 4 of these coccidia within 11 postinoculation days. The female cats were caged with 4 male Toxoplasma-free cats, starting 66 days after inoculation with Toxoplasma, until they were 5 to 6 weeks pregnant. Kittens that were born were housed with their mothers until necropsied or weaned. One 42-day-old kitten shed T gondii oocysts in feces. It was necropsied 2 days later and asexual stages of Toxoplasma (types D and E), gametocytes, and oocysts were demonstrated in sections of superficial epithelial cells of its small intestine. Lesions or forms of Toxoplasma were not demonstrated histologically in tis extraintestinal organs. Toxoplasma was not isolated from feces or tissues of the remaining 47 kittens born to these 8 queens. Toxoplasma was not isolated from the 4 male cats that were caged with infected females for 53, 59, 217, and 217 days. The source of toxoplasma infection in the kitten remained unknown but was considered unlikely to be congenital or through fecal contamination. Oocysts of I felis, I rivolta, and H hammondi were not found in the feces of any kittens, indicating that these coccidia are unlikely to be transmitted congenitally.     

Correlation of tissue infection and serologic findings in pigs fed Toxoplasma gondii oocysts

Each of thirteen 6-week-old pigs was inoculated per os with 10,000 sporulated oocysts of Toxoplasma gondii. By postinoculation day (PID) 13, pigs were seropositive by the indirect fluorescent antibody test. Beginning on PID 13 and every 7 days thereafter through PID 97, 1 pig was killed and 6 tissues were examined for T gondii. Of the 13 pigs, 11 were infected, including the 1st pig killed on PID 13, although none of the pigs had gross lesions of toxoplasmosis. Tissues harboring T gondii most frequently were the heart and brain; organisms were detected less frequently in the longissimus muscles, diaphragm, and liver. Toxoplasma gondii was not detected in the bronchial lymph nodes. There was good correlation between antibody and presence of T gondii in these pigs. One additional pig, maintained as a noninfected control, remained seronegative and had no evidence of infection when killed on PID 97.     

The development of a molecular approach for coprodiagnosis of Toxoplasma gondii

Copro-diagnostic methods for Toxoplasma gondii infected cats have been traditionally based on the identification of oocysts by light microscopy or by bioassays. The first method is not sensitive and also unable to differentiate between Toxoplasma oocysts from other coccidian parasites in cats, and the second is cumbersome, time consuming and expensive. We have adapted a polymerase chain reaction (PCR) method to detect T. gondii oocyst DNA in fecal samples. Oocysts were successfully disrupted by freeze thawing coupled with mechanical means, and DNA extraction was subsequently accomplished. The test, based on amplifying a 529 bp repeated sequence, proved sensitive for detecting 1-2 oocysts in 200 microg of stool sample. The test specificity was established by showing that DNA from other cat coccidia tested negative. Specificity was reconfirmed by Southern hybridization of the PCR products with a specific probe. Of 122 stool samples from Jerusalem cats surveyed for the presence of Toxoplasma oocysts, 11 were found positive by PCR while none was detected by microscopy.     

Isolation and molecular characterization of Toxoplasma gondii from chickens and ducks from Egypt

The prevalence of Toxoplasma gondii in free range chickens is a good indicator of the prevalence of T. gondii oocysts in the environment because chickens feed from the ground. In the present study, prevalence of T. gondii in 121 free range chickens (Gallus domesticus) and 19 ducks (Anas sp.) from a rural area surrounding Giza, Egypt was assessed. Blood, heart, and brain from each animal were examined for T. gondii infection. Antibodies to T. gondii, assayed with the modified agglutination test (MAT), were found in 49 (40.4%) chickens in titers of 1:5 in 11, 1:10 in four, 1:20 in four, 1:40 in eight, 1:80 in 10, and 1:160 or more in 12 chickens. Antibodies were found in three ducks each with a titer of 1:80. Hearts and brains of seropositive (MAT > or = 1:5) chickens and ducks were bioassayed in mice. Additionally, hearts and brains of seronegative (MAT<1:5) animals were bioassayed in T. gondii-free cats. T. gondii was isolated from 19 of 49 seropositive chickens (one with a titer of 1:5, two with a titer of 1:20, one with a titer of 1:40, five with a titer of 1:80, three with a titer of 1:160, and seven with a titer of > or = 1:360). One cat fed tissues pooled from 15 seronegative chickens shed T. gondii oocysts, while two cats fed tissues of 34 seronegative chickens did not shed oocysts. T. gondii was isolated from one of the seropositive ducks by bioassay in mice. The two cats fed tissues from 16 seronegative ducks did not shed oocysts. Genotyping of 20 chicken isolates of T. gondii using the SAG 2 locus indicated that 17 isolates were type III and three were type II. The duck isolate of T. gondii was type III. The mice inoculated with tissue stages of all 21 isolates of T. gondii from chickens and ducks remained asymptomatic, indicating that phenotypically they were not type I because type I strains are lethal for mice. Infections with mixed genotypes were not found.     

Incidence of Toxoplasma gondii oocysts in cat feces

Within two years and a half, the faeces of 620 cats coming from Brno and the area around the city were subjected to parasitological examination with special regard to the occurrence of the oocysts of Toxoplasma gondii. Sucrose solution at the specific weight of 1,150 was used as flotation medium. Oocysts of Toxoplasma gondii were eliminated by eight cats (1.29%) at the age from 16 days to 1.5 years. Six of the eight cats were younger than seven months. The Toxoplasma gondii oocysts were eliminated by the cats for 1-16 days while exhibiting signs of short-term scours and swelling of lymph nodes. In all cases the oocysts of Toxoplasma gondii were produced in the summer and autumn seasons (June-December). During the patent period, other coccidia (Isospora felis and Isospora rivolta) were also present in the cats.     

Genetic and biologic characterization of Toxoplasma gondii isolates of cats from China

Cats are important in the epidemiology of Toxoplasma gondii infection because they are the only hosts that can excrete the environmentally resistant oocysts. In the present study, prevalence of T. gondii was determined in serum, feces, and tissues of 34 cats from People's Republic of China. Antibodies to T. gondii were assayed by the modified agglutination test and found in 27 of 34 (79.4%) cats with titers of 1:40 in one, 1:80 in one, 1:160 in three, 1:320 in three, 1:640 in eight, and 1:1280 or higher in 11 cats. T. gondii oocysts were not found in feces of any cat as ascertained by bioassay in mice. Tissues (brain, heart, and tongue) of 27 seropositive cats were pooled and bioassayed in mice (8 cats) or cats (19 cats). T. gondii was isolated from tissues of 17 of 27 seropositive cats. Genotyping of these 17 T. gondii isolates using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and a new SAG2, and an apicoplast marker Apico revealed two genotypes. This is the first report of genetic typing of T. gondii isolates from cats from China.     

Examination of cats for the elimination of Toxoplasma gondii oocysts]

Two hundred and two samples of excrements were investigated for the presence of Toxoplasma gondii oocysts. Fifty-two samples were taken from dead domestic cats and a hundred and fifty samples were obtained from wild cats living in various localities of the CSSR. The investigation was orientative and a flotation method with the Breza flotation solution of the specific weight of 1.300 was used. If the finding was positive, residues of the excrements were floated with a saccharose, solution of the specific weight of 1.150 and containing 0.8% of phenol. The oocysts were rinsed several times, then they were sporulated in Petri dishes with water with a 2.5% solution of potassium dichromate. The sporulated oocysts, after rinsing, were injected i. p. to mice. The excrements of the fifty-two domestic cats were negative. Out of a hundred and fifty samples of the excrements of wild cats, one sample with the oocysts of isospore type was found; a biological test with mice proved the oocysts of Toxoplasma gondii. It may be inferred from the results obtained that the elimination of oocysts by cats is the same as given in foreign literature, and the occurrence rate will be about 2%.     

Prevalence and genotypes of Toxoplasma gondii in feline faeces (oocysts) and meat from sheep, cattle and pigs in Switzerland

The protozoan parasite Toxoplasma gondii infects almost all warm blooded animal species including humans, and is one of the most prevalent zoonotic parasites worldwide. Post-natal infection in humans is acquired through oral uptake of sporulated T. gondii oocysts or by ingestion of parasite tissue cysts upon consumption of raw or undercooked meat. This study was undertaken to determine the prevalence of oocyst-shedding by cats and to assess the level of infection with T. gondii in meat-producing animals in Switzerland via detection of genomic DNA (gDNA) in muscle samples. In total, 252 cats (44 stray cats, 171 pet cats, 37 cats with gastrointestinal disorders) were analysed coproscopically, and subsequently species-specific identification of T. gondii oocysts was achieved by Polymerase Chain Reaction (PCR). Furthermore, diaphragm samples of 270 domestic pigs (120 adults, 50 finishing, and 100 free-range animals), 150 wild boar, 250 sheep (150 adults and 100 lambs) and 406 cattle (47 calves, 129 heifers, 100 bulls, and 130 adult cows) were investigated by T. gondii-specific real-time PCR. For the first time in Switzerland, PCR-positive samples were subsequently genotyped using nine PCR-restriction fragment length polymorphism (PCR-RFLP) loci (SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico) for analysis. Only one of the cats shed T. gondii oocysts, corresponding to a T. gondii prevalence of 0.4% (95% CI: 0.0-2.2%). In meat-producing animals, gDNA prevalence was lowest in wild boar (0.7%; 95% CI: 0.0-3.7%), followed by sheep (2.0%; 95% CI: 0.1-4.6%) and pigs (2.2%; 95% CI: 0.8-4.8%). The highest prevalence was found in cattle (4.7%; 95% CI: 2.8-7.2%), mainly due to the high prevalence of 29.8% in young calves. With regard to housing conditions, conventional fattening pigs and free-range pigs surprisingly exhibited the same prevalence (2.0%; 95% CI: 0.2-7.0%). Genotyping of oocysts shed by the cat showed T. gondii with clonal Type II alleles and the Apico I allele. T. gondii with clonal Type II alleles were also predominantly observed in sheep, while T. gondii with mixed or atypical allele combinations were very rare in sheep. In pigs and cattle however, genotyping of T. gondii was often incomplete. These findings suggested that cattle in Switzerland might be infected with Toxoplasma of the clonal Types I or III, atypical T. gondii or more than one clonal Type.     

Genetic characterization of Toxoplasma gondii isolates in dogs from Vietnam suggests their South American origin

Dogs are considered a potential risk for transmission of Toxoplasma gondii to humans because they can mechanically transmit oocysts to people and in certain parts of the world dog meat is consumed by humans. The prevalence of T. gondii in 42 dogs from rural Vietnam was determined. Antibodies to T. gondii were assayed by the modified agglutination test, and found in 21 (50%) of 42 dogs with titers of 1:20 in six, 1:40 in seven, 1:80 in two, 1:160 in two, 1:320 in two, 1:640 in one, and 1:1280 or higher in one. Hearts, tongues and brains of 21 seropositive dogs were bioassayed in cats, mice or both. Tissues from eight seropositive dogs were fed to eight T. gondii-free cats. Feces of cats were examined for oocysts. T. gondii was isolated from eight dogs by bioassay in cats. Genotyping of these eight T. gondii isolates using polymorphisms at 10 nuclear markers including SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and a new SAG2, and an apicoplast marker Apico revealed two genotypes. Both genotypes were previously identified from the dog isolates in Colombia, suggesting their South America origin. However, they are different from the predominant Type I, II and III lineages that are widely spread in North America and Europe. This is the first report of isolation of viable T. gondii from any host in Vietnam.     

Unexpected oocyst shedding by cats fed Toxoplasma gondii tachyzoites: in vivo stage conversion and strain variation

Tachyzoites, bradyzoites (in tissue cysts), and sporozoites (in oocysts) are the three infectious stages of Toxoplasma gondii. The prepatent period (time to shedding of oocysts after primary infection) varies with the stage of T. gondii ingested by the cat. The prepatent period (pp) after ingesting bradyzoites is short (3-10 days) while it is long (18 days or longer) after ingesting oocysts or tachyzoites, irrespective of the dose. The conversion of bradyzoites to tachyzoites and tachyzoites to bradyzoites is biologically important in the life cycle of T. gondii. In the present paper, the pp was used to study in vivo conversion of tachyzoites to bradyzoites using two isolates, VEG and TgCkAr23. T. gondii organisms were obtained from the peritoneal exudates (pex) of mice inoculated intraperitoneally (i.p.) with these isolates and administered to cats orally by pouring in the mouth or by a stomach tube. In total, 94 of 151 cats shed oocysts after ingesting pex. The pp after ingesting pex was short (5-10 days) in 50 cats, intermediate (11-17) in 30 cats, and long (18 or higher) in 14 cats. The strain of T. gondii (VEG, TgCKAr23) or the stage (bradyzoite, tachyzoite, and sporozoite) used to initiate infection in mice did not affect the results. In addition, six of eight cats fed mice infected 1-4 days earlier shed oocysts with a short pp; the mice had been inoculated i.p. with bradyzoites of the VEG strain and their whole carcasses were fed to cats 1, 2, 3, or 4 days post-infection. Results indicate that bradyzoites may be formed in the peritoneal cavities of mice inoculated intraperitoneally with T. gondii and some bradyzoites might give rise directly to bradyzoites without converting to tachyzoites.     

Soil contamination of Toxoplasma gondii oocysts in pig farms in central China

Toxoplasmosis in pigs is a large threat to pig industry as well as pork consumers. Most pigs become infected by ingestion of oocysts from contaminated environment (soil, water and feed) or infected animal tissues postnatally. In the present study, field studies were conducted to evaluate the relationship between soil contamination status of Toxoplasma gondii oocysts and T. gondii infection in pigs in 12 pig farms with different density of cats in central China. The presence of T. gondii oocysts in soil were determined by PCR and loop-mediated isothermal amplification (LAMP). T. gondii DNA was found in 11 farms with different cat density excepting one farm exposed to low cat density. Twenty (21.1%) and 36 (37.9%) of 95 soil samples were T. gondii positive by PCR and LAMP, respectively (0.01相似文献