A neurological disease in dogs whose pathogens were similar to toxoplasma but could not be classified was first described in Norway in 1984. In 1988, a similar pathogen was found in dogs in the USA and was named Neospora caninum. It was later determined that Neospora caninum was identical to the Norwegian pathogen. Neosporosis has already been detected in many countries, it must therefore be assumed that it is spread worldwide. Natural infections have been found in dogs, cattle, horses, sheep, goats, red deer and cats. Numerous other animals can be experimentally infected.
Clinically, dogs and cattle are particularly severely affected. In the latter, at every stage of gestation, the clinical picture is determined by abortions. In dogs, neurological signs are prominent: ascending paralysis of the hind legs with hyperextension are a typical finding, but all limbs might be affected as well (tetraplegia). Other possible findings are dysphagia, paralysis of the jaw, head tilt, muscle weakness, cardiac insufficiency and pneumonia. Young, congenitally infected dogs show more severe signs, sometimes with sudden deaths. Older dogs often show signs of disseminated infection with polyradiculitis, polymyositis and possibly multiple organ involvement. Thus, in older dogs with neurological signs, neosporosis should always be included in the differential diagnosis. However, due to the often high antibody prevalence in certain regions, it is assumed that only a small percentage of infected dogs actually develops a clinical disease.