The epidemiology of ovine toxoplasmosis. III. Observations on outbreaks of clinical toxoplasmosis in relation to possible mechanisms of transmission

Perdas reprodutivas associadas com infecção por Toxoplasma gondii em caprinos no sul do Brasil

Infecção por Toxoplasma gondii foi associada com perdas reprodutivas em um rebanho caprino no Rio Grande do Sul, Brasil. Lesões macroscópicas foram observadas em dois de seis produtos caprinos enviados para diagnóstico e incluíram linfonodos mesentéricos pálidos e aumentados e pulmões com consistência firme e áreas claras intercaladas com vermelhas. Lesões histológicas, especialmente caracterizadas por infiltrados linfoplasmocitários no cérebro e pulmões, foram observadas em todos os fetos. Nefrite intersticial linfoplasmocitária, linfadenite necrosante e hepatite periportal linfoplasmocitária também foram observadas. Enquanto tanto o exame bacteriológico quanto o teste de imunofluorescência direta para Leptospira sp. foram negativos em todos os casos, a PCR e a imunoistoquímica resultaram positivamente para T. gondii em quase todas as amostras testadas. Anticorpos anti-T.gondii, em titulações de 1:512 a 1:2048, foram detectados nas amostras de soro sangüíneo das cabras que pariram natimortos (3), abortaram (1) ou cujos neonatos morreram (2). Este trabalho descreve os achados clínicos, patológicos, sorológicos, imunoistoquímicos e de PCR observados em um rebanho caprino infectado por T. gondii.

Seroepidemiology of sheep toxoplasmosis in Babol northern Iran 2004

This study is carried-out with the aim of determining the prevalence rate of toxoplasmosis in sheep at Babol (Bandpei part). In this study, 285 sheep of Bandpei area in Babol was selected. The samples studied with indirect immunofluorescence antibody. The results showed that 31.2% of sheep in this study were affected by toxoplasmosis. In positive cases, there was not any statistically significant difference between male and female sheep. The most positive cases observed by 1:200 titer. According to the researches in other parts of this country, the prevalence rate in this area is more than the others.

Toxoplasma gondii infections in sheep in Sicily, southern Italy

The aim of the study was to determine the burden of Toxoplasma gondii-infections in sheep in Sicily, southern Italy and the risk factors for infection. Sera from 1961 sheep were collected just before slaughtering from 62 farms located in 8 out of 9 Sicilian administrative districts. The sera were analysed for Toxoplasma-specific IgG antibodies using commercially available enzyme-linked immunosorbent assay. Sheep less than 4 weeks old were further analysed by ELISA for Toxoplasma-specific IgM-antibodies. Data on farm size and location were obtained from slaughterhouse sanitary reports and through structured telephone interviews of the veterinary officers from public health districts. The overall seroprevalence of Toxoplasma-specific IgG-antibodies were 49.9% (937/1876) by ELISA. Eighty-seven (54/62) percent of the farms had at least one Toxoplasma-positive animal. All the farms fed the animals outdoor on pasture and only one was claiming organic farming. Having cats on the farm, age of the animals, farm size and the use of surface water sources for drinking were all significantly associated with T. gondii-infected animals on the farm. T. gondii infection in mutton used for human consumption is very prevalent, and eating unprocessed sheep and lamb meat has a high risk of transmitting infections to humans. The presence of cats on the farm, farm size and using surface water as drinking water for the animals were risk factors for infection in sheep, with age as a significant confounder.

The parasite connection in ecosystems and macroevolution

In addition to their obvious negative effects ("pathogens"), endoparasites of various kinds play an important role in shaping and maintaining modern animal communities. In the long-term, parasites including pathogens are indispensable entities of any ecosystem. To understand this, it is essential that one changes the viewpoint from the host's interests to that of the parasite. Together with geographic isolation, trophic arms race, symbiosis, and niche partitioning, all parasites (including balance strategists, i.e. seemingly non-pathogenic ones) modulate their hosts' population densities. In addition, heteroxenic parasites control the balance between predator and prey species, particularly if final and intermediate hosts are vertebrates. Thereby, such parasites enhance the bonds in ecosystems and help maintain the status quo. As the links between eukaryotic parasites and their hosts are less flexible than trophic connections, parasite networks probably contributed to the observed stasis and incumbency of ecosystems over geologic time, in spite of continuous Darwinian innovation. Because heteroxenic parasites target taxonomic levels above that of the species (e.g. families), these taxa may have also become units of selection in global catastrophies. Macroevolutionary extrapolations, however, are difficult to verify because endoparasites cannot fossilize.

Significant familial differences in the frequency of abortion and Toxoplasma gondii infection within a flock of Charollais sheep

A study was carried out to investigate the frequencies of abortion and congenital Toxoplasma gondii infection within 27 families (765 individuals) of a pedigree Charollais sheep flock maintained on a working farm in Worcestershire, UK, since 1992. Pedigree lambing records were analysed to establish the frequency of abortion for each family. The frequency of congenital infection was determined for each family by PCR analysis of tissue samples taken from newborn lambs. A total of 155 lambs were tested for congenital T. gondii infection, which were all born during the study period 2000–2003. Significant differences in the frequency of abortion between sheep families within this flock were observed with frequencies ranging between 0% and 48% (P<0·01). Significantly different infection frequencies with T. gondii were also observed for different families and ranged between 0% and 100% (P<0·01). Although the actual cause of each abortion was not verified, a highly significant positive correlation was found to exist between the frequency of abortion and the frequency of T. gondii infection in the same families (P<0·01). The data presented here raise further questions regarding the significance of congenital transmission of T. gondii within sheep populations, the possible successive vertical transmission of T. gondii within families of sheep, and the potential role of inherited genetic susceptibility to abortion with respect to T. gondii infection. This work invites further study into the epidemiology of ovine toxoplasmosis and may have implications for sheep husbandry methods in the future.

Evaluation of ovine abortion associated with Toxoplasma gondii in Spain by different diagnostic techniques

A total of 173 aborted ovine foetuses and seven aborted caprine foetuses, submitted from different points of north and central Spain, were analysed to determine the role of T. gondii in abortion and to compare the utility of the most widely used techniques in diagnosis of the congenital infection (histopathology, serology--IFAT and ELISA--and a nested-PCR). Parasite infection was diagnosed in 40 (23.1%; n = 173) ovine foetuses by at least one of the diagnostic techniques used. A higher percentage of foetuses were diagnosed using serological techniques (IFAT and ELISA) (28.3%; n = 106) than by histologic examination (8.7%; n = 173) or PCR (6.9%; n = 173). No significant association between infection and the foetal age categories was found (P > 0.05). In this study, 106 aborted foetuses were analysed by all of the three diagnostic techniques. When we compared serological results, perfect agreement between ELISA and IFAT was obtained. On the contrary, slight to fair agreements were observed when histology results were compared with those obtained by serology and PCR techniques. All the positive foetuses were aborted in the mid (60%) or last (40%) term of pregnancy, but no significant differences were found between ages of the infected and non-infected foetuses (P > 0.05). This report indicates that toxoplasmosis may be a common cause of small ruminant abortion and neonatal death in Spain and points out the necessity of using different and complementary techniques to increase the probability of detecting Toxoplasma infection in an aborted foetus.

Survey of ovine and caprine toxoplasmosis by IFAT and PCR assays in Sardinia, Italy

During the period 1999-2002, we have analyzed 9639 serum samples and 815 aborted samples (670 fetuses and 145 placenta) from 964 ovine and caprine farms distributed over all Sardinia island. After abortion notification, sera collected at random from adult animals were examined to detect simultaneously IgG and IgM antibodies specific to Toxoplasma gondii by indirect immunofluorescence assay, whereas fetuses and placenta were analyzed by a single tube nested PCR assay. Specific IgG antibodies were detected in 2048 (28.4%) sheep and 302 (12.3%) goats, specific IgM antibodies were found in 652 (9%) sheep and 139 (5.6%) goats. From a total of 2471 ovine and 362 caprine fetal samples including muscle, liver, abomasum, spleen, brain and placenta, 271 (11.1%) ovine and 23 (6.4%) caprine samples were T. gondii PCR-positive. Although T. gondii DNA was amplified from different types of tissues, placenta was the tissue with the highest detection rate. On the one hand, these results indicate that the seroprevalence of T. gondii infection in sheep and goats is relatively high, on the other PCR results demonstrate that T. gondii has a significant role in ovine and caprine abortion. Adequate management might be useful and essential to control the toxoplasmosis in the sheep and goats herds of Sardinia.

High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock

Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.

Acute phase toxoplasma abortions in sheep

Within 13 days of the experimental infection of 15 oestrus-synchronised ewes with 2000 sporulated oocysts of Toxoplasma gondii at 80 to 90 days of gestation 11 had aborted. The infection induced pyrexia and specific antibody in all the ewes. One ewe resorbed its fetus, 11 ewes aborted and three delivered, at full term, live congenitally infected lambs whose pre-colostral serum was antibody-positive. Tissues from the aborted fetuses and placentae from the live lambs were examined for toxoplasma infection by polymerase chain reaction (PCR) amplification of the B1 gene and by mouse inoculation. The live lambs were all shown to be infected by both methods, but there was no evidence of infection in any of the tissues from the acute phase abortions, suggesting that these fatalities occurred before the placenta or the fetus had been invaded by T gondii. Such toxoplasma-induced, acute-phase abortions are likely to be impossible to diagnose from fetal tissues. These results have implications not only for the diagnosis of naturally occurring ovine abortions but also for the understanding of the pathogenesis of toxoplasma-induced abortion.

The incidence and economic significance of ovine toxoplasmosis in Uruguay

Antibodies to Toxoplasma gondii were measured before and after pregnancy in a 1:64 dilution of sera with the direct agglutination test in 1613 ewes from 18 farms in 8 different counties of Uruguay from 1992 to 1994. The overall seroprevalence increased from 28.7% before mating to 38.5% after lambing in 2.5 yr and thus, the incidence was 9.8%. Losses due to toxoplasmosis during pregnancy were estimated to be 1.4 to 3.9% of the total number of ewes investigated, amounting to approximately US$1.4-4.7 million for the whole country.

Decoquinate and the control of experimental ovine toxoplasmosis

Decoquinate was tested for its ability to reduce the effect of experimentally induced toxoplasmosis in pregnant ewes. Sheep were given decoquinate in their feed daily at either 2 mg or 1 mg/kg bodyweight from 10 days before an oral challenge with Toxoplasma gondii oocysts at 90 days of gestation, until lambing. Feeding decoquinate at the higher rate caused a delay in the onset of the febrile response to infection, reduced the overall severity of the fever and delayed the production of antibodies to the parasite. This treatment also reduced the placental damage caused by the parasite, lengthened the mean gestation period and increased the number and weight of live lambs, in comparison with ewes not fed decoquinate but challenged with T gondii oocysts. The treatment with 1 mg of decoquinate had smaller effects.

Prevalence of agglutinating antibodies to Toxoplasma gondii in small ruminants of the Madrid region, Spain, and identification of factors influencing seropositivity by multivariate analysis

A seroepidemiological survey of Toxoplasma gondii infection in sheep and goats was conducted in the Madrid region of Spain. Sera were collected from 60 herds, for which farming management information and other relevant data for their characterization were also obtained through a questionnaire. The seroprevalence was 11.8% (64 out of 541), using the modified (2-mercaptoethanol) direct agglutination technique with a 1:64 cut-off titre. The relationship between seropositivity and the variables in the questionnaire was assessed by multivariate analysis. Four variables were found to be significantly associated with seroprevalence. Two of them, the presence of cats and a previous history of abortion outbreaks in the farm, were factors known to be linked with toxoplasmosis, indicating the validity of the serological data. Seropositivity was also related to a lack of replacements in the preceding year. Proximity to other farms appeared to be a protective factor negatively associated with seropositivity, probably because it was an indicator of proximity to an urban area and the availability of local sanitary facilities.

Investigations with enzyme-linked immunosorbent assays for Trichinella spiralis and Toxoplasma gondii in the Dutch 'Integrated Quality Control for finishing pigs' research project

In the framework of the Dutch field trial 'Integrated Quality Control (IQC) for finishing pigs' ELISA (screening) techniques were used to detect animals seropositive for Toxoplasma gondii and/or Trichinella spiralis. The aim was to determine whether farms which consistently delivered seropositive pigs could be detected and monitored (defined as 'problem farms'). The investigation involved 120 farms and three slaughterhouses, and a total of 23,348 serum samples were examined. In addition, all pigs were also screened for the presence of Trichinella spiralis with the digestion method (pooled samples). The prevalence of seropositivity for Trichinella spiralis and Toxoplasma gondii was 0.3% and 2.1% respectively. Parasitological examinations concerning T. spiralis were negative. Considering the characteristics of the used methodology, the conclusion was drawn that there were no parasitological or serological indications for T. spiralis infections, and that with respect to T. gondii the infection rate seemed to be equally low for all farms involved. In addition, a longitudinal pilot study during a whole finishing period was undertaken at two finishing farms. Animals seropositive for Toxoplasma gondii were found from the earliest days of the finishing period. Housing and management may (still) play an important role in the prevention of contact with this parasite.

Further studies in the use of monensin in the control of experimental ovine toxoplasmosis

Monensin was fed to 69 pregnant ewes from 81 to 84 days gestation until lambing, at an estimated rate of nil, 16.8 or 27.9 mg per head per day. Ten days after the start of this regime, groups of the ewes were dosed orally with nil, 2000 or 12,000 sporulated Toxoplasma gondii oocysts. Twenty ewes given T. gondii alone (T ewes) produced 29 lambs or aborted foetuses, 16 (55.2 per cent) of which were born dead. The 39 ewes given monensin and T. gondii (M + T ewes) produced 48 lambs or aborted foetuses, 8 (16.7 per cent) of which were born dead. The 10 ewes given monensin alone produced 12 live lambs. No difference of effect was apparent between the two doses of monensin given, nor between the two doses of Toxoplasma oocysts used. Monensin alone caused no discernible problems. Not only were proportionately more live lambs born to M + T ewes than to T ewes, but they were also heavier, possibly due to a lesser "weight" of infection within the gravid uterus. We conclude that monensin fed at about 16 mg per head per day to pregnant ewes can significantly reduce losses at lambing time due to experimentally administered T. gondii.