Life Cycle of Neospora caninum

The life cycle of N. caninum includes intermediate and definitive hosts and consists of an asexual and a sexual cycle. The asexual cycle occurs in the intermediate hosts (cattle, sheep, goats and horses) and definitive hosts (dogs and coyotes). The sexual cycle only occurs in the definitive hosts.

Neospora caninum is a protozoal parasite belonging to the phylum Apicomplexa. The characteristics of the parasite are comparable to those of Toxoplasma gondii.

During the life cycle of N. caninum we can identify the following stages:

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• oocyst
• sporozoites
• bradyzoites
• tachyzoites
• tissue cyst.

Sexual cycle (definitive host)

1. The definitive host eats material (aborted fetus, placenta or raw infected carcasses) containing N. caninum tissue cysts and is infected with the parasite.
2. Sexual multiplication takes place in the intestine of the definitive host and oocysts are produced.
3. N. caninum oocysts are excreted with the faeces of the definitive host.

Asexual cycle (intermediate and definitive host)

1. Cattle grazing on pastures or eating food contaminated by infected dog faeces ingest N. caninum oocysts.
2. In the gut sporozoites are released from the oocysts and penetrate the epithelium of the small intestine. The sporozoites then enter different tissues but are mostly found in the reticulo-endothelial system. Here they further differentiate into tachyzoites.
3. Tachyzoites reproduce rapidly asexually and invade different tissues and in pregnant animals the fetus via the placenta.
4. With the onset of the bovine immune response, tachyzoites revert to dormant bradyzoites within tissue cysts (found mainly in neural tissue).
5. During future pregnancies,in infected animals bradyzoites are reactivated and differentiate into tachyzoites that invade the fetus via the placenta.