Neosporosis in dogs: Signs and treatments

Neospora caninum, the causative organism of Neosporosis, is a microscopic intracellular protozoan, morphologically similar to Toxoplasma gondii.  Recognized in the 1980s infections prior to that date were incorrectly attributed to Toxoplasma. Dogs and coyotes are the definitive hosts of this parasite. A number of herbivores act as intermediate hosts. Recognized intermediate hosts include cattle, goats and deer.

A dog catches Neosporosis from eating raw or undercooked meat from an infected animal or congenitally from its dam. The intermediate hosts catch the parasite by grazing on land contaminated by the feces from an infected dog or coyote.  Within the intermediate hosts, Neospora caninum causes abortions in pregnant animals.

Neospora has three different cellular forms small tachyzoites, larger tissue cysts and the small oocysts, which pass out of the dog in its feces to infect other animals. The tachyzoites are 5 - 7 um long by 1.5 um wide. They live in muscle, skin, neural and other cells. The tissue cysts live in neural tissue and grow to about 100 um in diameter. Tissue cysts contain large numbers of a mature form of the parasite known as bradyzoites. Bradyzoites are similar in size to tachyzoites. The oocysts of Neospora caninum are 10 to 12 um in diameter.

Severe infections occur in dogs under six months old. These young dogs also represent the most common age group to exhibit the infection. Signs of Neospora infection in a young dog start as a gradual ascending paralysis affecting the limbs combined with muscle atrophy. Contracture of the muscles occurs in the affected limbs. The condition affects the dog’s rear legs more severely than its fore legs. Neospora infection sometimes leads to joint deformation in the limbs of a puppy.  Dysphagia (difficulty swallowing) and megaesophagus (lack of peristalsis) along with a cervical weakness occasionally occur leading to the death of the puppy.

Older dogs with Neosporosis develop polymyositis (muscle pain). Other less common signs of Neosporosis include skin ulceration, pneumonia, encephalitis and hepatitis. Fatal cases of Neosporosis occur in dogs of all ages.

In a litter of puppies born to an infected bitch, some puppies may be infected while others may not. Congenitally infected puppies may exhibit signs of infection between the ages of three to nine weeks. If one puppy shows evidence of Neosporosis, all its littermates require treatment. Early treatment frequently prevents an infected puppy becoming paralyzed. Unfortunately, treatment will not reverse paralysis in an already affected puppy.

A bitch with one infected litter runs a high risk of producing infected puppies in subsequent litters.  Many vets advocate the sterilization of infected bitches so preventing them from producing more infected puppies.

The antibiotics used for treating cases of Neosporosis in dogs sulfadiazine, clindamycin, and pyrimethamine (daraprim) are the same ones licensed for treatment of Toxoplasmosis in dogs. These drugs are use either singly or in combination.

Reference Sources:

Neosporosis in Dogs, J.P. Dubey The 30th Congress of the World Small Animal Veterinary Association

The Merck Veterinary Manual