Toxoplasma gondii: from animals to humans

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

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Epidemiology and Control of Neosporosis and Neospora caninum

Neospora caninum is a coccidian parasite of animals. It is a major pathogen for cattle and dogs and it occasionally causes clinical infections in horses, goats, sheep, and deer. Domestic dogs are the only known definitive hosts for N. caninum. It is one of the most efficiently transmitted parasite of cattle and up to 90% of cattle in some herds are infected. Transplacental transmission is considered the major route of transmission of N. caninum in cattle. Neospora caninum is a major cause of abortion in cattle in many countries. To elicit protective immunity against abortion in cows that already harbor a latent infection is a major problem. This paper reviews information on biology, diagnosis, epidemiology and control of neosporosis in animals.

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Review of Neospora caninum and neosporosis in animals.

Neosporosis in animals--the last five years.

The availability of immunotoxicity data for fungal toxins varies considerably for different toxins. The following is a comprehensive review of the most recent literature on the immunotoxicity of aflatoxins, fumonisins, gliotoxin, ochratoxins, patulin, and trichothecenes. Aflatoxin is an immunomodulating agent that acts primarily on cell-mediated immunity and phagocytic cell function. In addition to further characterization of aflatoxininduced immunotoxicity in various species, some recent studies have focused on ameliorating the effects of aflatoxin by supplementing or amending the diet. The immunomodulatory effects of ochratoxins have also been considered for many years. Notably, recent studies have examined immune function in the offspring of rats and mice exposed to ochratoxin pre- and perinatally. Fumonisin toxicity has been characterized relatively recently in comparison to aflatoxin and ochratoxin, and fumonisin-induced immunotoxicity is an area of active research. As these studies progress, they ma...

Immunomodulation by fungal toxins.

Neospora caninum is a major cause of abortion in cattle worldwide. Cattle become infected with N. caninum by ingesting oocysts from the environment or transplacentally from dam to fetus. Experimentally, dogs can act as definitive hosts, but dogs excrete few oocysts after ingesting tissue cysts. A natural definitive host was unknown until now. In the present study, N. caninum was isolated from the feces of a dog. Gerbils (Meriones unguiculatus) fed feces from the dog developed antibodies to N. caninum in the Neospora caninum agglutination test, and tissue cysts were found in their brains. Neospora caninum was isolated in cell culture and in gamma-interferon gene knockout mice inoculated with brain homogenates of infected gerbils. The DNA obtained from fecal oocysts of the dog, from the brains of gerbils fed dog feces, and from organisms isolated in cell cultures inoculated with gerbil brains was confirmed as N. caninum. The identification of N. caninum oocyst by bioassay and polymerase chain reaction demonstrates that the dog is a natural definitive host for N. caninum.

First Isolation of Neospora caninum From the Feces of a Naturally Infected Dog

Prevalence of Sarcocystis spp. in Argentinean cattle.

The aim of the study was to diagnose Sarcocystis sp. infections in cattle and to detect coinfections by Toxoplasma gondii and/or Neospora caninum. Blood, diaphragm, esophagus, and myocardium from 90 beef cattle from Argentina were collected. Histopathological, immunohistochemical, polymerase chain reaction assays, and direct microscopical examination were carried out. Sarcocysts from myocardium were measured and counted. Indirect fluorescent antibody test (IFAT) for the three protozoans was performed. Sarcocystis cruzi sarcocysts were found in 100% of myocardium samples. Sarcocysts per gram ranged from 8 to 380 with higher values found in adult cattle (p < 0.001). T. gondii and N. caninum were not detected by immunohistochemistry. T. gondii DNA was found in myocardium of 2/20 seropositive animals, while N. caninum DNA was not found. Antibodies against S. cruzi were detected in all samples, those against N. caninum in 73% and against T. gondii in 91% of the samples (IFAT titer ≥25). It is concluded that serology by IFAT is a suitable method to diagnose these protozoan infections due to its specific IgG detection; therefore, IFAT may be a useful tool to evaluate the impact of each protozoan infection in coinfected animals.

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Diagnosis of Sarcocystis cruzi , Neospora caninum , and Toxoplasma gondii infections in cattle

Prevalence of antibodies to Sarcocystis neurona, Toxoplasma gondii and Neospora caninum in horses from Argentina.

Prevalence of anti-Neospora caninum antibodies was de- termined in sera of 320 dogs from Argentina using the indirect fluores- cent antibody test (IFAT). Antibodies to N. caninum were found in 121 of 320 (37.8%) sera with titers of 1:50 (21 dogs), 1:100 (23 dogs), 1: 200 (23 dogs), 1:400 (17 dogs), 1:800 (23 dogs), and $1:1,600 (14 dogs). The seropositivity (IFAT, $ 1:50) was higher in dogs from dairy (48% of 125) and beef (54.2% of 35) farms than in dogs from urban areas (26.2% of 160). Prevalence of anti-N. caninum antibodies was higher in dogs more than 12 mo of age (47.7%, 105 of 222) versus in 12-mo-old or younger dogs (12.7% of 86), suggesting postnatal expo- sure of N. caninum infection in dogs. Neospora caninumis an important cause of mortality in dogs and cattle in many countries including Argentina (Dubey and Lindsay, 1996; Dubey, 1999; Venturini et al., 1999; Lindsay and Dubey, 2000). Until recently, vertical transmission from prevalence of antibodies (IFAT, $ 1:50) was higher in dogs from beef (54.2% of 35) and dairy (48% of 125) farms than from dogs from urban areas (26.2% of 160); the differences were statistically significant (P , 0.001). Of the 153 urban dogs, the seroprevalence in males (28.1% of 71) was not sta- tistically different ( P 5 0.86) from that in females (25.6% of 82). Of the 153 dogs with breed data, seroprevalence was 23.9% of 117 in purebred dogs versus 36.1% of 36 crossbred dogs (not significant P 5 0.21). The antibody titers in dogs with clinical signs were not different from those in dogs without reported clinical signs. Prevalence of antibodies increased with age of the dog with seroprevalence of: 13% of 46, #12-mo- old; 12.9% of 31, 13-24-mo-old; 34.3% of 32, 25-48-mo-old dogs; and 45.4% of 44, 49-mo or older dogs (significant P 5 0.001). Prevalence of N. caninum antibodies was significantly higher (P , 0.001) in dogs .12 mo of age (60.9% of 87) versus #12- mo-old dogs (9.6% of 31) from dairy farms. Although the num- ber of dogs from beef farms was low, similar trends were ap- parent; antibodies to N. caninum were found in 2 of 9 (22%), 12-mo-old or younger dogs versus 17 of 28 (60.7%) dogs older than 12 mo from the beef farms. Overall, prevalence in 12-mo- old or younger dogs (12.7% of all dogs of known age) was significantly lower (P 5 0.001) than in dogs older than 12 mo (47.7% of 222).

L. Venturini

Papers

First Isolation of Neospora caninum From the Feces of a Naturally Infected Dog

Prevalence of Sarcocystis spp. in Argentinean cattle.

Diagnosis of Sarcocystis cruzi , Neospora caninum , and Toxoplasma gondii infections in cattle

Prevalence of antibodies to Sarcocystis neurona, Toxoplasma gondii and Neospora caninum in horses from Argentina.

Prevalence of Neospora caninum infection in dogs from beef-cattle farms, dairy farms, and from urban areas of Argentina.