Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis

Seroprevalence of Toxoplasma gondii infection among veterinary staff in Ontario, Canada (2002): implications for teratogenic risk

BACKGROUND

Toxoplasma gondii infection is embryotoxic in humans. It is mainly transmitted through raw/undercooked meat and ingestion of oocysts in cat feces. There remains controversy about the actual risk of cats transmitting the disease to humans. Our primary objective was to determine the seroprevalence of T. gondii antibody among veterinary staff, to ascertain whether they have an increased risk through occupational exposure. Our secondary objective was to examine their practices regarding cats, toxoplasma infection, and pregnancy.

METHODS

Veterinary staff attending the 2002 Annual Ontario Veterinary Medical Association Conference were invited to discuss their toxoplasma seroprevalence. Interested attendees completed a questionnaire and a physician drew blood samples to determine T. gondii titres using the ELISA IgG test.

RESULTS

We collected 161 completed questionnaires, and 141 blood samples. There were 20 (14.2%, CI 95%:8.4-19.9%) reactive titres among the veterinarian staff (80% females aged 30-45). All were regularly exposed to cats, washed their hands when in contact and few wore gloves routinely.

CONCLUSIONS

These findings of low positive rates may be used to reassure veterinary staff that their exposure to cats does not appear to increase their risk of contracting toxoplasma infection and that pregnant women are not at an increased risk by owning a cat.

Seroepidemiology of Toxoplasma gondii in dogs in Trinidad and Tobago

A cross-sectional study was conducted to determine the seroprevalence of Toxoplasma gondii agglutinins and to investigate the relationship between various risk factors and occurrence of toxoplasmosis in dogs in Trinidad. Of a total 250 dogs, comprising domestic, hunting and stray dogs, 80 (32.0%) were positive for T. gondii agglutinins at a titre of > or =1:32 using a latex agglutination test. Stray dogs (60.5%) had statistically significantly higher (P<0.001) seroprevalence for toxoplasmosis than hunting dogs (30.5%) and domestic dogs (25.5%). Amongst dogs whose ages were known, the prevalence of toxoplasmosis was significantly highest (P=0.037) in dogs in the >2-3 years age group compared with other age groups. Dogs that consumed home-cooked foods had a seroprevalence of 32.9% compared with those fed commercial dog foods (17.2%) and dogs fed both home-cooked and commercial foods (21.0%). However, the difference was not statistically significant (P>0.05; chi(2)). The rather high prevalence of toxoplasmosis in stray dogs is a good indication of the extent of the infection in the environment.

Pregnancy as a risk factor for acute toxoplasmosis seroconversion

OBJECTIVE

To test the hypothesis that pregnancy is a risk factor for toxoplasmosis seroconversion.

MATERIALS AND METHODS

A prospective observational study of women at child-bearing age vulnerable to Toxoplasma gondii. Serological reactions with indirect immunofluorescent antibody and immunoenzyme tests were used. The risk estimate used limits of reliability at 95%, and the results were validated by chi(2) and RR tests.

RESULTS

Acute infection among pregnant women was 8.6% (45/522), and pregnancy was confirmed to be a risk factor for seroconversion (P=0.001). Living in close contact with host animals and vehicles of oocyst transmission proved to be a statistical risk for pregnant women to seroconvert, which was aggravated in adolescents.

CONCLUSION

Gestation, potentiating susceptibility to this infection, points to the need of primary and secondary prevention for all pregnant women at risk.

Incidence of congenital toxoplasmosis in southern Brazil: a prospective study

The study aimed to determine the incidence of congenital infection by Toxoplasma gondii and to describe neonatal and maternal characteristics regarding newborn infants treated at a teaching hospital in the town of Passo Fundo, State of Rio Grande do Sul, Brazil. Cord blood samples collected from 1,250 live newborns were analyzed. The laboratory diagnosis was established by the detection of Toxoplasma gondii IgM using an enzyme linked fluorescent assay. Gestational age, intrauterine growth, anthropometric measures, and prenatal characteristics were assessed. The incidence of congenital toxoplasmosis at birth was 8/10,000 (95%CI 0.2-44.5). Mean birthweight was 3,080 +/- 215.56 grams and mean gestational age was 38.43 +/- 1.88 weeks. With regard to prenatal care, 58% of the pregnant patients visited their doctors five times or more and 38.9% were serologically tested for toxoplasmosis in the first trimester of pregnancy. The incidence of congenital toxoplasmosis was similar to that found in most studies conducted in our country and abroad. Our study sample is representative of the town of Passo Fundo and therefore it is possible to consider the frequency observed as the prevalence of the disease in this town during the study period.

Serological survey of Toxoplasma gondii infection in pigs slaughtered in Sweden

The prevalence of Toxoplasma gondii infection in Swedish pigs was investigated by analysis of 807 meat juice samples collected in 1999 from 10 abattoirs in different parts of the country. When analysed using ELISA, 42 (5.2%) of the samples were found to be positive. The seroprevalence was 3.3% in fattening pigs (n = 695) and 17.3% (n = 110) in adult swine. Alternative interpretations of the results, considering estimates of the true prevalence based on the sensitivity and specificity of the test method, are discussed. It is concluded that the risk of contracting T. gondii infection as a result of eating undercooked pork from Swedish pigs, especially adult animals, is not negligible.

Molecular evidence for multiple Toxoplasma gondii infections in individual patients in England and Wales: public health implications

We sought to determine the SAG2 genotypes of Toxoplasma gondii associated with cases of acute human toxoplasmosis in England and Wales. The samples examined were collected from a wide range of cases including congenital infections, AIDS and immunosuppressed patients and were derived from a number of different tissues. Parasite DNA was detected by PCR amplification without the need for prior template purification, and SAG2 genotype was determined by both restriction enzyme analysis and direct DNA sequencing of the PCR amplification products. Parasites of both SAG2 type I and type II genotypes were seen with approximately equal frequency amongst the samples examined. Neither of these genotypes was found to be more frequently associated with a particular clinical presentation or sample tissue. Unexpectedly, we found clear evidence of mixed (SAG2 type I+type II) infections in approximately the same number of samples as were seen to be associated with either type I or II alone. Our use of direct DNA sequencing rather than simple restriction analysis was essential for the detection of mixed infections since incomplete restriction digestion of samples containing a single parasite type was occasionally observed. It is possible that the presence of more than one type of parasite in single samples might be related to our recent demonstration that mixtures of SAG2 type I and type II parasites are present in a significant proportion of commercial meat preparations. Moreover, the presence of mixed infections in single patients might offer a direct molecular method of assessing risk factors for infection.

Highly endemic, waterborne toxoplasmosis in north Rio de Janeiro state, Brazil

In Campos dos Goytacazes, northern Rio de Janeiro state, Brazil, reports of uveitis consistent with toxoplasmosis led to a survey of the prevalence and risk factors for Toxoplasma gondii infection in 1997-1999. The survey population was selected randomly from schools, randomly chosen communities, and an army battalion. Serum samples from 1,436 persons were tested. With results adjusted for age, 84% of the population in the lower socioeconomic group was seropositive, compared with 62% and 23% of the middle and upper socioeconomic groups, respectively (p<0.001). When multivariate analysis was performed, drinking unfiltered water was found to increase the risk of seropositivity for the lower socioeconomic (odds ratio [OR]: 3.0, 95% confidence interval [CI] 1.3 to 6.9) and middle socioeconomic (OR: 1.7, 95% CI 1.2 to 2.3) populations. We also found a high T. gondii seroprevalence in this Brazilian community. Drinking unfiltered water increased the risk of T. gondii seropositivity, indicating the potential importance of oocyst transmission in water in this region.

Enteric parasitic zoonoses of domesticated dogs and cats

Dogs and cats are important members of many families; however, they can harbour gastrointestinal parasites that may infect their owners. Some of these parasites, e.g. Echinococcus sp., can have a significant impact on human health. However, with appropriate education, management and anthelmintic regimes, zoonotic transmission of these parasites can be minimised.

Serological survey of Toxoplasma gondii, feline immunodeficiency virus and feline leukaemia virus in urban stray cats in Belgium

Three hundred and forty-six serum samples taken between 1998 and 2000 from urban stray cats in the city of Ghent were tested for antibodies to Toxoplasma gondii and feline immunodeficiency virus (FIV), and antigens of feline leukemia virus (FeLV). Of these 346 samples, 243 (70.2 per cent) were seropositive for Tgondii. Thirty-nine cats (11.3 per cent) had antibodies against FIV and 13 (3.8 per cent) had circulating antigens of FeLV. Fewer of the female cats had FIV and heavier cats had a higher seroprevalence of FIV. Exact logistic regression showed that cats that were infected with FIV were more likely to be infected with T gondii (P = 0.04), and the cats with FIV had a higher titre of Tgondii antibodies than FIV-negative animals. However, FeLV was not associated with either T gondii or FIV.

Toxoplasma gondii: transmission, diagnosis and prevention

Toxoplasmosis, caused by the protozoan parasite Toxoplasma gondii, is one of the most common parasitic infections of man and other warm-blooded animals. It has been found world-wide from Alaska to Australia. Nearly one-third of humanity has been exposed to this parasite. In most adults it does not cause serious illness, but it can cause blindness and mental retardation in congenitally infected children and devastating disease in immunocompromised individuals.

Primary Toxoplasma gondii infection in a pregnant human immunodeficiency virus-infected woman

We report a 36-year-old HIV-infected woman who developed primary Toxoplasma gondii infection during pregnancy that was treated with spiramycin and antiretroviral drugs. There was no vertical transmission of toxoplasmosis and HIV.

Calculating sample size bounds for logistic regression

The calculation of a study's required sample size is one of the most important aspects of the validity of an epidemiological study. Logistic regression often is used in modelling in epidemiology. A simplified method to calculate the sample size for the multiple logistic-regression model was proposed by Hsieh et al. [Stat. Med. 17 (1998) 1623]. The approach for estimating the sample size is described and then applied in the planning of an epidemiological cross-sectional study of the associations of different risk factors with Toxoplasma infection among pregnant women. Although the method demands some additional information which is often difficult to obtain, it is a very useful tool in veterinary epidemiology.

A theoretical analysis of the relations between the risk of congenital toxoplasmosis and the annual infection rates with a convincing argument for better public intervention

In a theoretical analysis of the present study, we quantitatively indicate a potential threat of congenital toxoplasmosis to Japanese young women by the use of a simple mathematical model or a special case of the well-known catalytic infection model. For introducing a risk function of congenital toxoplasmosis, an annual infection rate, r, was divided into r(1), the rate before age a(0 < a < 15), and r(2), the rate after age a. Presuming the values of r(1), r(2) and a on the basis of the current situation of Toxoplasma infection in Japan, simulation analyses were performed with the mathematical model. As the simulation clearly demonstrated, Japanese young women are potentially facing a threat of congenital toxoplasmosis, although the current risk of it is relatively lower. From the viewpoint of risk management, public intervention programs are required. Based on our analyses, public intervention programs can be classified into two groups: group 1 for women before age a and group 2 for those after age a, and each group is expected to give a different kind of effect to the risk of congenital toxoplasmosis. The present study implies that a certain public intervention program could augment the risk, inadvertently.

Epidemiology of congenital toxoplasmosis identified by population-based newborn screening in Massachusetts

BACKGROUND

Fourteen years of newborn screening in Massachusetts for congenital toxoplasmosis infection identified subpopulations that appeared to have higher rates of infection. Elaborating an epidemiologic profile and risk correlates might aid implementing targeted prenatal education and newborn screening strategies with the goal of early postnatal treatment to prevent morbidity.

OBJECTIVE

To describe the epidemiology of congenital toxoplasmosis in Massachusetts and risk correlates of infection using birth certificate data.

METHODS

A case-control study was conducted based on Massachusetts birth certificate data. Cases were all infants with congenital toxoplasmosis identified by statewide universal newborn screening from 1988 to 1999. Controls were all children born on the same day as those infants in Massachusetts.

RESULTS

Factors that strongly predicted congenital toxoplasmosis infection were mother's country of birth outside the US (especially the southeast Asian refugee origin countries of Cambodia and Laos), mother's educational level and higher gravidity.

CONCLUSIONS

More extensive, culturally and linguistically appropriate, prenatal education is needed for pregnant women, regardless of a mother's educational level, especially for non-US-born mothers, and not focused only on primiparous women. Other states may be able to use their state-specific birth certificate data to compare risk profiles with those of Massachusetts to guide a toxoplasmosis screening policy on the basis of population similarities and differences.

Seroprevalence of antibodies to Toxoplasma gondii in lynx (Lynx canadensis) and bobcats (Lynx rufus) from Québec, Canada

The seroprevalence of antibodies to Toxoplasma gondii was investigated in trapped lynx (Lynx canadensis) and bobcats (Lynx rufus) from Québec, Canada. Forty-seven of 106 (44%) lynx and 4 of 10 (40%) bobcats had positive titers for T. gondii (> or = 25) by means of the modified agglutination test incorporating mercaptoethanol and formalin-fixed tachyzoites. Seroprevalence was significantly higher (P < 0.0001) in adult lynx than in juvenile lynx. The presence of antibodies to T. gondii in lynx and bobcats suggests that this organism is widespread in the wild and that exposure to wild felids and game animals from Québec may represent a potential source of infection for humans.

Congenital toxoplasmosis: a review

Toxoplasmosis is caused by infection with the protozoan parasite Toxoplasma gondii. In the United States, approximately 85% of women of childbearing age are susceptible to acute infection with T. gondii. Acute infections in pregnant women may cause serious health problems when the organism is transmitted to the fetus (congenital toxoplasmosis), including mental retardation, seizures, blindness, and death. An estimated 400 to 4000 cases of congenital toxoplasmosis occur in the U.S. each year. Manifestations of congenital toxoplasmosis may not become apparent until the second or third decade of life. Serologic tests are used to diagnose acute infection in pregnant women, but false-positive tests occur frequently, therefore, serologic diagnosis must be confirmed at a reference laboratory before treatment with potentially toxic drugs should be considered. Much of congenital toxoplasmosis can be prevented by educating women of childbearing age and pregnant women to avoid eating raw or undercooked meat, to avoid cross-contamination of other foods with raw or undercooked meat, and to use proper cat-litter and soil-related hygiene.

Toxoplasma gondii: from animals to humans

Toxoplasmosis is one of the more common parasitic zoonoses world-wide. Its causative agent, Toxoplasma gondii, is a facultatively heteroxenous, polyxenous protozoon that has developed several potential routes of transmission within and between different host species. If first contracted during pregnancy, T. gondii may be transmitted vertically by tachyzoites that are passed to the foetus via the placenta. Horizontal transmission of T. gondii may involve three life-cycle stages, i.e. ingesting infectious oocysts from the environment or ingesting tissue cysts or tachyzoites which are contained in meat or primary offal (viscera) of many different animals. Transmission may also occur via tachyzoites contained in blood products, tissue transplants, or unpasteurised milk. However, it is not known which of these routes is more important epidemiologically. In the past, the consumption of raw or undercooked meat, in particular of pigs and sheep, has been regarded as a major route of transmission to humans. However, recent studies showed that the prevalence of T. gondii in meat-producing animals decreased considerably over the past 20 years in areas with intensive farm management. For example, in several countries of the European Union prevalences of T. gondii in fattening pigs are now <1%. Considering these data it is unlikely that pork is still a major source of infection for humans in these countries. However, it is likely that the major routes of transmission are different in human populations with differences in culture and eating habits. In the Americas, recent outbreaks of acute toxoplasmosis in humans have been associated with oocyst contamination of the environment. Therefore, future epidemiological studies on T. gondii infections should consider the role of oocysts as potential sources of infection for humans, and methods to monitor these are currently being developed. This review presents recent epidemiological data on T. gondii, hypotheses on the major routes of transmission to humans in different populations, and preventive measures that may reduce the risk of contracting a primary infection during pregnancy.

Emerging parasite zoonoses associated with water and food

The environmental route of transmission is important for many protozoan and helminth parasites, with water, soil and food being particularly significant. Both the potential for producing large numbers of transmissive stages and their environmental robustness, being able to survive in moist microclimates for prolonged periods of time, pose a persistent threat to public and veterinary health. The increased demands on natural resources increase the likelihood of encountering environments and produce contaminated with parasites. For waterborne diseases, the protozoa, Cryptosporidium, Giardia and Toxoplasma, are the most significant causes, yet, with the exception of Toxoplasma, the contribution of zoonotic transmission remains unclear due to the absence of 'standardised' methods. The microsporidia have been documented in one waterborne outbreak, but the role of animals as the cause of contamination was not elucidated. In foods, surface contamination is associated with the faecal-oral pathogens, and some data are available to indicate that animal wastes remain an important source of contamination (e.g. cattle faeces and apple cider outbreaks), however, further work should focus on examining the source of contamination on fruit and vegetables. Increasing recognition of the burden of human fascioliasis has occurred; it is now recognised as an emerging zoonosis by the WHO. Toxoplasma, Trichinella and Taenia spp. remain important meatborne parasites, however, others, including Pleistophora-like microsporidians may be acquired from raw or lightly cooked fish or crustaceans. With increased international travel, the public health importance of the foodborne trematodiases must also be realised. Global sourcing of food, coupled with changing consumer vogues, including the consumption of raw vegetables and undercooking to retain the natural taste and preserve heat-labile nutrients, can increase the risk of foodborne transmission. A greater awareness of parasite contamination of our environment and its impact on health has precipitated the development of better detection methods. Robust, efficient detection, viability and typing methods are required to assess risks and to further epidemiological understanding.