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).     

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.     

Prevention of shedding and re-shedding of Toxoplasma gondii oocysts in experimentally infected cats treated with oral Clindamycin: a preliminary study

This work aimed to evaluate the effects of preventive oral Clindamycin in cats infected with Toxoplasma gondii. Twelve short hair cats were divided into two groups (group 1 and group 2). No titres of T. gondii antibodies were detected in these cats before the experiment. The animals from group 1 were infected with tissue cysts of T. gondii and group 2 were infected and treated with Clindamycin (20 mg/kg/day). The infection was done with almost 40-50 tissue cysts for each cat on day 0. The cats from group 2 were treated with Clindamycin by oral rout for 24 days (from day -3 to day 21). At day 45, the groups 1 and 2 were divided into two subgroups with three animals each. Subgroups 1A and 2A were immunosuppressed with dexamethasone (1 mg/kg/day) for30 days and subgroups 1B and 2B were not immunosuppressed. Faecal exam looking for oocyst shedding was made by 30 days after T. gondii infection, and for 30 days after immunosuppression. All kittens from group 1 shedding oocysts after infection, while animals from group 2 did not shed. After immunosuppression period, all animals from group 1A re-shed oocysts and animals from group 2A remained without shed. However, 2 (66.6%) of the kittens from subgroup 2B shed oocysts 19-20 days after re-challenge. Based on this preliminary study, Clindamycin had a complete inhibitory effect on shedding of oocysts by cats, even under severe immunosuppression, which is a new finding not reported elsewhere.     

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.     

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   

Isolation and characterization of Toxoplasma gondii strains from stray cats revealed a single genotype in Beijing, China

Cats are essential in the epidemiology of Toxoplasma gondii because they are the only hosts that can excrete the environmentally resistant oocysts in nature. This study was aimed to determine the seropositivity, distribution of genotypes and mouse virulence of T. gondii from stray cats in Beijing, China. A total of 64 serum samples, 23 feces and tissue samples were collected from stray cats in Beijing. Antibodies to T. gondii were assayed by the modified agglutination test (MAT). 57.8% (37/64) of these stray cats had titers of 1:20 or higher and were considered positive with infection. T. gondii oocysts were not found in feces of the 23 cats. Tissues of 23 cats were bioassayed in mice and 11 T. gondii isolates were obtained. The genotype of these isolates were identified by 11 PCR-RFLP markers, including SAG1, (3'+5')SAG2, alt.SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1, and an apicoplast marker, Apico. Only one genotype was identified. This genotype, designated as ToxoDB genotype #9, was previously reported in cats, pigs and human from Guangdong and Gansu provinces in China and animals from a few other countries. To determine mouse virulence of this lineage of parasites, one isolate was randomly selected and inoculated into BABL/c mice, the result showed that it is intermediately virulent to mice. These results indicated that an atypical, intermediately virulent T. gondii lineage is widespread in China. The high seropositivity of T. gondii in stray cats posts potential risk of transmission of the parasite to human population in the region.     

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.     

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 and biologic characteristics of Toxoplasma gondii infections in free-range chickens from Austria

The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in free-range chickens (Gallus domesticus) from 11 Bio-farms in Austria was determined. Antibodies to T. gondii assayed by the modified agglutination test (MAT) were found in 302 of 830 (36.3%) chickens with titers of 1:10 in 50, 1:20 in 69, 1:40 in 53, 1:80 in 40, 1:160 or higher in 90. Hearts of 218 chickens with MAT titers of 10 or higher were bioassayed individually in mice. Tissues from 1183 chickens were pooled and fed to 15, T. gondii-free cats. Feces of the cats were examined for oocysts; 11 cats shed T. gondii oocysts. T. gondii was isolated from 56 chickens by bioassay in mice. Thus, there were 67 isolates of T. gondii from these chickens. Genotyping of these 67 isolates using the SAG2 locus indicated that all 33 were Type II. Phenotypically and genetically these isolates were different from T. gondii isolates from Brazil. None of the isolates was virulent for mice. This is the first report of isolation of T. gondii from chickens from Austria.     

Experimental infection of budgerigars (Melopsittacus undulatus) with a low virulent K21 strain of Toxoplasma gondii

In total 53 budgerigars (Melopsittacus undulatus) were divided into six groups and orally infected with a suspension of oocysts of low virulent Toxoplasma gondii K21 strain in the doses of 10(2), 10(3), 10(4), 10(5) and 10(6), respectively. Blood was collected from the birds prior to the inoculation and then on days 10, 20 and 30 post infection. Latex-agglutination test (LAT) was used for the detection of antibodies in the inoculated birds. The infected birds showed no apparent signs of disease. The antibodies were found in all but two birds inoculated a dose of 10(2) oocysts. Haematological values remained unchanged after infection. T. gondii was isolated by bioassay in mice from all 37 birds fed 10(3) or more oocysts and 6 of 9 fed 10(2) oocysts. The results demonstrate that budgerigars are resistant to T. gondii infection.     

In vitro isolation and seroprevalence of Toxoplasma gondii in stray cats and pigeons in Lisbon, Portugal

Oral contamination with Toxoplasma gondii oocysts shed by cats into the environment has been linked to severe outbreaks of human toxoplasmosis. Pigeons (Columba livia) are highly susceptible to oral infection with oocysts and indirectly indicate soil contamination, since they feed from the ground. A seroprevalence study was performed on cats and pigeons captured in the city of Lisbon. Serum samples collected from 1507 pigeons captured at 64 feeding sites and 423 stray cats were screened for antibodies anti-T. gondii using a commercial direct agglutination test. Seroprevalence in pigeons was 2.6% (39/1507) (95% CI: 1.9-3.5%) and 37.5% (24/64) of pigeon flocks sampled showed to be infected with T. gondii. The proportion of infected pigeons within seropositive flocks ranged between 4.8% and 21.1%. Among cats, seroprevalence was 44.2% (187/423) (95% CI: 39.5-49.1%). Isolation of T. gondii from animal tissues was attempted by in vitro assay. Inoculation of brain homogenates from 20 pigeons and 56 cats into Vero cell cultures allowed isolation of T. gondii from 13 pigeons (65%) and 15 cats (26.8%). Inoculation of muscle homogenates (heart and limbs) prepared by acid-peptic digestion from a subset of 15 cats resulted in the recovery of T. gondii from 10 cats (66.7%).     

Occurrence of Toxoplasma gondii and Hammondia hammondi oocysts in the faeces of cats from Germany and other European countries

Faecal samples of 24,106 cats from Germany and other European countries were examined microscopically in a veterinary laboratory in Germany between October 2004 and November 2006 to estimate the prevalence of animals shedding Toxoplasma gondii or Hammondia hammondi oocysts. Oocysts of 9-15 microm size with a morphology similar to that of H. hammondi and T. gondii were found in 74 samples (0.31%). A total of 54 samples were further characterised to achieve a species diagnosis and to determine the genotype of T. gondii isolates by PCR and PCR-RFLP. From these samples, 48 isolates were obtained: 26 (0.11%) were finally identified as T. gondii and 22 (0.09%) as H. hammondi. T. gondii-positive samples came from Germany, Austria, France and Switzerland while H. hammondi was detected in samples from Germany, Austria and Italy. In two samples (one T. gondii and one H. hammondi), PCR indicated the presence of Hammondia heydorni DNA. No Neospora caninum DNA was detected in any of the feline faecal samples. Twenty-two of the 26 T. gondii isolates could be genotyped. A PCR-RFLP analysis for the SAG2, SAG3, GRA6 and BTUB genes revealed T. gondii genotype II in all cases. Morphologically, H. hammondi oocysts exhibited a statistically significantly smaller Length-Width-Ratio than T. gondii oocysts.     

Serological survey and risk factors for Toxoplasma gondii in domestic ducks and geese in Lower Saxony, Germany

To obtain estimates for the prevalence of Toxoplasma gondii infection in ducks and geese in Germany, enzyme-linked immunosorbent assays (ELISA) were established based on affinity-purified T. gondii tachyzoite surface antigen 1 (TgSAG1) and used to examine duck and goose sera for T. gondii-specific antibodies. The results of 186 sera from 60 non-infected ducks (Anas platyrhynchos) and 101 sera from 36 non-infected geese (Anser anser) as well as 72 sera from 11 ducks and 89 sera from 12 geese inoculated experimentally with T. gondii tachyzoites (intravenously) or oocysts (orally) and positive in a T. gondii immunofluorescent antibody test (IFAT) were used to select a cut-off value for the TgSAG1-ELISA. Sera obtained by serial bleeding of experimentally inoculated ducks and geese were tested to analyze the time course of anti-TgSAG1 antibodies after inoculation and to assess the sensitivity of the assays in comparison with IFAT. In ducks, IFAT titres and ELISA indices peaked 2 and 5 weeks p.i with tachyzoites, respectively. Only three of six geese inoculated with tachyzoites at the same time as the ducks elicited a low and non-permanent antibody response as detected by the IFAT. In the TgSAG1-ELISA, only a slight increase of the ELISA indices was observed in four of six tachyzoite-inoculated geese. By contrast, inoculation of ducks and geese with oocysts led to an increase in anti-TgSAG1 antibodies within 1 or 2 weeks, which were still detectable at the end of the observation period, i.e. 11 weeks p.i. Inoculation of three ducks and three geese with oocysts of Hammondia hammondi, a protozoon closely related to T. gondii, resulted in a transient seroconversion in ducks and geese as measured by IFAT or TgSAG1-ELISA. Using the newly established TgSAG1-ELISA, sera from naturally exposed ducks and geese sampled in the course of a monitoring program for avian influenza were examined for antibodies to T. gondii; 145/2534 (5.7%) of the ducks and 94/373 (25.2%) of the geese had antibodies against TgSAG1. Seropositive animals were detected on 20 of 61 duck and in 11 of 13 goose farms; the seroprevalences within positive submissions of single farms ranged from 2.2% to 78.6%. Farms keeping ducks or geese exclusively indoors had a significantly lower risk (odds ratio 0.05, 95% confidence interval 0.01-0.3) of harboring serologically positive animals as compared with farms where the animals had access to an enclosure outside the barn.     

Genetic and biologic characteristics of Toxoplasma gondii isolates in free-range chickens from Colombia, South America

The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 77 free-range chickens (Gallus domesticus) from Colombia, South America was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT), and found in 32 (44.4%) of 72 chickens with titers of 1:5 in 4, 1:10 in 3, 1:20 in 1, 1:40 in 1, 1:80 in 8, 1:160 in 8, 1:320 in 3, and 1:640 or higher in 4. Hearts and brains of 31 seropositive chickens were pooled and bioassayed in mice. Tissues from 32 (16+16) seronegative chickens were pooled and fed to two, T. gondii-free cats, and tissues from nine chickens without matching sera were fed to one T. gondii-free cat. Feces of cats were examined for oocysts. T. gondii oocysts were excreted by a cat that was fed tissues of 16 seronegative chickens. T. gondii was isolated by bioassay in mice from 23 chickens with MAT titers of 1:20 or higher. All infected mice from 16 of the 23 isolates died of toxoplasmosis. Overall, 82 (81.1%) of 101 mice that became infected after inoculation with chicken tissues died of toxoplasmosis. Genotyping of these 24 isolates using polymorphisms at the SAG2 locus indicated that seven T. gondii isolates were Type I, 17 were Type III, and none was Type II. Phenotypically, T. gondii isolates from chickens from Colombia were similar to isolates from Brazil but different from the isolates from North America; most isolates from chickens from Brazil and Colombia were lethal for mice whereas isolates from North America did not kill inoculated mice. Genetically, none of the T. gondii isolates from Colombia and Brazil was SAG2 Type II, whereas most isolates from chickens from North America were Type II. This is the first report of genetic characterization of T. gondii isolates from Colombia, South America.     

Comparison of different commercial DNA extraction kits to detect Toxoplasma gondii oocysts in cat faeces

The cat is the definitive host of Toxoplasma gondii and plays an important role in the transmission of this and other coccidian parasites, e.g. Hammondia hammondi, a protozoon closely related and morphologically similar to T. gondii. A number of techniques to detect T. gondii nucleic acids in feline faeces are described and several extraction kits for isolating pathogen DNA from faeces or soil are commercially available. To compare the performance of such kits with regard to isolating oocyst DNA, a feline sample that had tested negative for coccidian parasites including T. gondii and H. hammondi was spiked with 10(4), 10(3), 10(2), 50 and 10 H. hammondi oocysts. Several ready-to-use stool or soil kits and an in-house method were then used to extract parasite DNA from these spiked faecal samples. Of six kits tested, two were found suitable for the detection of H. hammondi oocysts DNA by the polymerase chain reaction (PCR) in faecal samples with a detection limit of 250 oocysts per 1 g of faecal sample. These two kits revealed a similar, even slightly lower detection limit (50 oocysts per 1 g of sample) when tested with faecal samples spiked with T gondii oocysts.     

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.     

Infection dynamic of Toxoplasma gondii in two fattening pig farms exposed to high and low cat density in an endemic region

The presence of cats in the farms is considered a risk factor for the infection of pigs with Toxoplasma gondii (T. gondii). Cats eliminate oocysts that contaminate food, water and promote the infection of host reservoir such as rodents and birds among others that are also involved in the infection of pigs. The objective of this study was to assess the dynamic of infection of T. gondii in seronegative weaned pigs from weaning to 20 weeks of age from two farms from an endemic region, one with high and low density of cats. A cohort study was performed in 64 pigs, 31 newly weaned pigs on a farm with a high density of cats (FA) and 33 newly-weaned pigs on a farm with a low density of cats (FB). Blood samples were collected every 14 days to determine the presence of IgG antibodies against T. gondii in the serum using an indirect ELISA test. True incidence rate (TIV), cumulative incidence (AI) and relative risk (RR) was calculated. The age of seroconversion was determined by using survival tables; both farms were compared with Long-Rank test. In FA 97.5% of the pigs seroconverted at the second sampling and 100% at the third sampling, while in the FB all pigs seroconverted to the fourth sampling. The TIV was 0.67 and 0.43 for FA and FB respectively, during the first four weeks at risk. A RR of 1.5 (1.04-2.39) was obtained (p<0.05). Animals of the FA had a higher risk of infection compared with the FB, however, all animals included in the study had contact with the agent. Infection with T. gondii was rapidly distributed in both farms, regardless of the relative density of cats observed during the study. These results suggest a high environmental contamination with oocysts in the facilities of both farms probably due to the fact that T. gondii infection is endemic in the area where the farms are located, allow proper establishment of the etiological agent. The points of prevention and control strategies to avoid exposure of pigs to T. gondii in an endemic area should focus on the control of cats and rodents.     

Characterization of Toxoplasma gondii isolates in free-range chickens from Chile, South America

The prevalence of Toxoplasma gondii in free-ranging chickens is a good indicator of the prevalence of T. gondii oocysts in the soil because chickens feed from the ground. The prevalence of T. gondii in 85 free-range chickens (Gallus domesticus) from Chile was determined. Antibodies to T. gondii were assayed by the modified agglutination test (MAT), and found in 47 of 85 (55.3.9%) chickens with titers of 1:5 in six, 1:10 in four, 1:20 in four 1: 40 in three, 1: 80 in nine, 1: 160 in four 1:320 in nine, and 1: 640 or higher in eight. Hearts and brains of 47 chickens with titers of 1:5 or higher were pooled for each chicken and bioassayed in mice. Tissues from 16 seronegative (MAT<1:5) chickens were pooled and fed to one T. gondii-free cat. Feces of the cat were examined for oocysts but none was found based on bioassay of fecal floats in mice. Hearts and brains from seven seronegative (<1:5) were pooled and bioassayed in mice; T. gondii was not isolated. T. gondii was isolated by bioassay in mice from 22 chickens with MAT titers of 1:20 or higher. Genotyping of these 22 isolates using polymorphisms at the loci SAG1, SAG2, SAG3, BTUB and GRA6 revealed three genotypes. Seventeen isolates had type II alleles and four isolates had type III alleles at all loci. One isolate contained the combination of type I and III alleles. This is the first report of genetic characterization of T. gondii isolates from Chile, South America.     

Serologic response of red-legged partridges (Alectoris rufa) after oral inoculation with Toxoplasma gondii oocysts

Thirty 5-month-old red-legged partridges (Alectoris rufa) reared in battery were divided into five groups: 4 birds in group A, 14 birds in group B, 4 birds in group C, 4 birds in group D and 4 birds in group E, and were inoculated orally with 10, 50, 10(2), 10(3) and 10(4) oocysts of the OV-51/95 strain of Toxoplasma gondii, respectively. During the experiment, blood samples from all birds were drawn every 3-7 days and at necropsy. Serologic response was measured by the modified agglutination test (MAT) and the latex agglutination test (LAT). One bird from each group was killed at 44, 58, 65 and 72 days after inoculation (DAI). From 72 DAI to the end of the experiment, surviving partridges from group B were killed at weekly intervals. The last partridges were sacrified 100 DAI. MAT was the most sensitive and specific test for detecting T. gondii antibodies in the birds. First positive titers were detected by MAT in all sera on 7 DAI, but titers by LAT did not appear until 13 DAI. Antibody titers detected by MAT on 7 DAI were higher in the partridges with the largest inocula (10(3) or 10(4) oocysts) than those inoculated with 10, 50 or 10(2) oocysts. All surviving birds developed a serologic response to T. gondii, with maximum titers of 512-32,768 in the MAT on 13-17 DAI, and positive titers persisted at least until 100 DAI. To the contrary, LAT reveals only very low antibody titers even in partridges inoculated with the highest dose of T. gondii.