TABLE OF CONTENTS
Neosporosis in Dogs and Cattle: Causes, Clinical Signs, Diagnosis, Treatment & Control
Neosporosis is an important protozoal disease caused by Neospora caninum, a tissue cyst-forming coccidian parasite that primarily affects dogs and cattle. Dogs serve as the definitive host, while cattle are the most economically important intermediate host due to reproductive losses, particularly abortion. This article provides an overview of the morphology, transmission, clinical signs, diagnosis, treatment, and control of neosporosis in dogs and cattle.
Neosporosis is an emerging disease caused by the tissue cyst-forming coccidian parasite, Neospora caninum. It was first reported in 1984 in Boxer dogs in Norway. It causes neuromuscular disorders (polyradiculoneuritis, myositis, and paralysis) in dogs, as well as neonatal mortality and abortion in cattle. It may also cause clinical disease in horses, goats, sheep, rhinoceroses, and deer. The dog is the only definitive host, but it also serves as an intermediate host.
Morphology
Three developmental stages are found in the life cycle: tachyzoites, bradyzoites (tissue cysts), and oocysts.
The oocysts are round, approximately 10 µm in diameter, and are morphologically similar to Toxoplasma gondii. Sporulated oocysts are spherical to subspherical and measure approximately 11.7 × 11.3 µm. The micropyle, oocyst residuum, and polar granules are absent.
Tachyzoites are ovoid, lunate, or globular in shape and are found in neural cells, macrophages, fibroblasts, vascular endothelial cells, myocytes, renal tubular epithelial cells, and hepatocytes. Tissue cysts are oval in shape and are found in the brain, spinal cord, and retina. The cyst wall is smooth, approximately 4 µm thick, and contains branched tube-like structures, but septa are absent.
Transmission
Dogs acquire infection by ingesting infected tissues, and congenital transmission also occurs. In cattle, vertical (transplacental) transmission is the primary mode of infection. Cattle may also become infected by ingesting oocysts present in contaminated feed.
In Dogs
Clinical Signs
N. caninum causes cell death through the active multiplication of tachyzoites and is capable of producing necrotic lesions. The most severe cases of neosporosis occur in young, congenitally infected puppies. Young dogs develop hind limb paresis that progresses to paralysis.
The hind limbs are more severely affected than the forelimbs and are often rigidly hyperextended. Other clinical signs include difficulty swallowing, jaw paralysis, muscle flaccidity, muscle atrophy, and even heart failure.
Dogs with hind limb paralysis may remain alert and survive for several months. Dermatitis may also be observed. Dogs of any age can be affected. Subclinically infected bitches can transmit the parasite to their fetuses, and successive litters from the same bitch may be born infected.
Diagnosis
- Based on clinical signs (ascending paralysis in young dogs).
- Increased serum enzyme levels associated with myocyte necrosis and liver damage.
- IFAT is the most commonly used diagnostic test (titer >1:200 to more than 1:600).
- Detection of antibodies in the cerebrospinal fluid is diagnostic.
- Tachyzoites should be identified in the CSF in cases of hind limb paralysis.
Treatment
- Trimethoprim and sulfadiazine: 15 mg/kg twice daily.
- Pyrimethamine: 1 mg/kg for 4 weeks.
- Clindamycin hydrochloride: 7.5 mg/kg for 45 days.
In Cattle
Clinical Signs
Abortion is an important clinical sign of bovine neosporosis. Cows of any age may abort from 3 months of gestation to term.
However, abortions most commonly occur at 5–6 months of gestation. Fetuses may die in utero, be resorbed, mummified, autolyzed, stillborn, or be born alive but clinically affected. Calves infected with neosporosis may exhibit neurological signs.
The hind limbs and forelimbs may be flexed or hyperextended, and affected calves may be unable to stand. Clinical signs include ataxia, exophthalmos, or an asymmetrical appearance of the eyes.
Diagnosis
- Histological examination of a freshly aborted fetus.
- Postmortem examination revealing lesions in the heart and central nervous system (CNS).
- ELISA can be used to diagnose neosporosis.
Treatment
There is no effective treatment for neosporosis in cattle.
Control and Prevention
- Prevent contamination of cattle feed and water with dog feces.
- Properly dispose of aborted fetuses and placentas by incineration.
- Dogs should not be allowed to consume aborted fetuses or fetal membranes.
