Neospora caninum is a microscopic protozoan parasite that can cause disease in various animal species. Identified in 1988, it was previously confused with Toxoplasma gondii due to structural similarities. This parasite is a major cause of reproductive failure in cattle and neurological disease in dogs, reported in many countries including the United States, New Zealand, and the Netherlands.
What is Neospora caninum?
Neospora caninum is an obligate intracellular protozoan parasite, meaning it must live inside the cells of another organism to survive and reproduce. It belongs to the phylum Apicomplexa, a group that includes Toxoplasma gondii. The parasite exists in different forms throughout its life cycle: oocysts, tachyzoites, and bradyzoites. Oocysts are the environmental stage, shed in feces. Tachyzoites are rapidly dividing forms that spread through tissues, while bradyzoites are slower-dividing forms that create cysts within the tissues of infected animals.
How Does It Spread?
Neospora caninum has a complex life cycle involving both definitive and intermediate hosts. Dogs and other canids, such as coyotes, gray wolves, and dingos, serve as definitive hosts, meaning the parasite undergoes its sexual reproductive stage in their intestines. These hosts shed unsporulated oocysts in their feces, which then sporulate in the environment, becoming infective.
Intermediate hosts, including cattle, sheep, goats, and deer, become infected by ingesting these sporulated oocysts from contaminated feed or water. A significant route of transmission in cattle is vertical transmission, where the parasite passes from an infected mother to her offspring during pregnancy.
Who Does It Affect and What Are the Signs?
Neospora caninum affects a variety of animals, with cattle and dogs being the most commonly and severely impacted. In cattle, the parasite is a major cause of reproductive issues, primarily leading to abortions, especially during the mid-to-late stages of gestation (three to nine months). Stillbirths and the birth of weak calves or calves with neurological problems are also common outcomes. This reproductive failure can result in economic losses for both dairy and beef industries.
In dogs, particularly young puppies infected congenitally, neosporosis often manifests as neurological signs. These can include progressive paralysis, frequently affecting the hind limbs, leading to muscle rigidity, ataxia (lack of coordination), and muscle atrophy. The prognosis for severely affected puppies is poor. Adult dogs may exhibit other signs such as inflammation of the brain, spinal cord, skin, liver, lungs, or heart. Other hosts like sheep, goats, and horses can also be infected, showing neurological or reproductive signs, though the disease is less prevalent in these species.
Diagnosis and Management
Diagnosing Neospora caninum infection involves several methods. Serological tests, which detect antibodies to the parasite in blood samples, are commonly used in live animals to identify exposure. Histopathology, the microscopic examination of tissue samples, is particularly useful for confirming infection in aborted fetuses or affected tissues. Additionally, PCR testing can detect the parasite’s DNA, providing a direct confirmation of its presence in various samples.
Currently, there is no effective treatment to eliminate the parasite, especially in animals with chronic infections. In dogs, symptomatic treatment with anti-protozoal drugs may be attempted, but its effectiveness can be limited, particularly in severe cases. Prevention and control strategies are therefore important. These include preventing dogs from accessing aborted fetal material or placentas from livestock, ensuring the proper disposal of dead livestock, and controlling canine access to cattle feed to minimize the spread of infective oocysts. In severely affected cattle herds, culling seropositive animals can be considered, though this decision is often complex due to economic and ethical factors.
Is it a Risk to Humans?
Neospora caninum is not considered a pathogen for humans. While some studies have detected antibodies to the parasite in certain human populations, there is currently no clear evidence of clinical disease or widespread illness directly caused by Neospora caninum infection in people. The primary concern for this parasite remains its impact on animal health, particularly in livestock and canids.