Parasitic Diseases of the Central Nervous System: The Global Burden

In a recent publication, Arturo Carpio, MD, Universidad de Cuenca, Ecuador, and colleagues discussed the burden of parasitic diseases of the central nervous system (CNS) and summarized some of the most important aspects of their clinical features, diagnosis, treatment, and control.

This article is the first in a 3-part series. It will discuss the burden of these diseases and will highlight some of the most common signs and symptoms associated with these conditions.

Burden of Disease

Parasitic diseases that affect the central nervous system (CNS) cause a substantial burden of disease, disability, and death, globally, especially in low- and middle-income countries. Although these diseases are endemic to certain regions, they have also spread to non-endemic regions as a result of the increase in world travel.

The epidemiology of parasitic diseases within the CNS has also been significantly changed by other factors, such as immunosuppression associated with HIV infection, post-transplantation therapy, and long-term corticosteroid treatment. Immunosuppressed individuals are at a particularly increased risk of infection with parasites such as Toxoplasma species.

According to the authors, approximately one billion people worldwide are affected by neglected tropical diseases (NTDs). These diseases are considered neglected because they occur mostly in the poorest populations. Several parasitic diseases of the CNS—including cysticercosis, echinococcosis, malaria, American trypanosomiasis, and African trypanosomiasis—are among these NTDs.

Although CNS involvement is possible in infection caused by any parasite that can infect humans, it is most commonly associated with cysticercosis, which is caused by larval cysts of the tapeworm Taenia solium. CNS involvement is less common with diseases such as toxoplasmosis, echinococcosis, and schistosomiasis, and rare with others such as malaria, American trypanosomiasis (Chagas disease), and human African trypanosomiasis (HAT).

CNS parasitic infections are highly burdensome. For example, in areas with poor sanitation and pig management practices and where pork is consumed and the tapeworm Taenia solium is endemic, the burden of epilepsy is almost 6.8 million disability-adjusted life years (DALYs). In these areas, mortality due to CNS cysticercosis is 3 to 6 times higher than in the general population.

In addition, malaria accounts for more than 3% of all DALYs and is ranked seventh among the top leading causes of DALYs worldwide. In 2015, an estimated 438,000 deaths were related to malaria.

The economic burden of parasitic diseases is also extremely high. For example, the estimated cost burden of cysticercosis in India is US $15.27 million. Similarly, the estimated cost burden of Chagas disease in Latin America is US $1.2 billion per year, associated with 752,000 work days lost annually because of premature deaths.

Clinical Manifestations

Most parasitic infections of the CNS result in similar clinical features, in particular, seizures. Other common, nonspecific clinical manifestations associated with many of the aforementioned diseases include headache, fever, cognitive abnormalities, focal deficits, visual disturbances.

“Almost all parasitoses involving the human brain can be associated with seizures and epilepsy, either by a diffuse encephalitis or encephalopathy, or by intracerebral location of the parasite,” the authors emphasize.

“Crossover between signs and symptoms, such as seizures, eosinophilia (in blood or CSF) and fever, occurs with many parasitic infections, thus making differential diagnosis a challenge,” they conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals, and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.