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Neospora caninum

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Neosporosis

3. Introduction

Neospora caninum is a coccidian parasite that was identified as a species in 1988. Prior to this, it was misclassified as Toxoplasma gondii due to structural similarities. Neospora caninum is an important cause of spontaneous abortion in infected livestock. Neospora caninum has a heteroxenous life cycle, with the reproductive stage occurring in the intestine of the definitive host, which is the dog. Other carnivores, for example, the fox, may also be definitive hosts. Oocysts passed in the feces of the definitive host are ingested by an intermediate host, for example, cattle, and form tissue cysts. Transplacental transmission, that is passage from mother to offspring during pregnancy, has been shown to occur in dogs, cats, sheep and cattle. The life cycle is typified by 3 infectious stages: tachyzoites, tissue cysts, and oocysts. Neospora caninum does not appear to be infectious to humans. In dogs, Neospora caninum can cause neurological signs, especially in congenitally infected puppies, where it can form cysts in the central nervous system (Wiki: Neospora caninum).

4. Microbial Pathogenesis

Neospora undergoes a life cycle involving three principle stages. First, oocysts are produced in the faeces of dogs, the definitive host, following ingestion of bradyzoites. Second, bradyzoites, which multiply slowly, are found in tissue cysts in the central nervous system (CNS), both in the canine definitive host and in a wide range of intermediate hosts. They represent a persistent, quiescent infection, held in check by host immunity. Third, tachyzoites, the rapidly multiplying stage, trigger lesion development by multiplying in and rupturing cells. In the absence of a host immune response, tachyzoites would continue to multiply, causing progressively more cell death until the host dies (Buxton et al., 2002).

5. Host Ranges and Animal Models

Dogs are the definitive host for Neospora caninum, but cattle can be infected, with infections causing abortion in cattle. There are no suitable animal models at the present to perform bioassay to detect N. caninum oocysts in dog feces. Although interferon-gamma gene knockout (KO) mice are highly susceptible to parenteral inoculation with N. caninum tachyzoites and tissue cysts, they are less susceptible to parenteral ororal inoculation with oocysts. Gerbils (Meriones unguiculatus) were susceptible to N. caninum infection with oocysts. Another species of gerbils, Meriones tristrami and sand rats (Psammoomys ubesus) also susceptible to tachyzoites infection (Dubey, 2003).

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