Neurocysticercosis is an infection of the brain by larvae of the pork tapeworm parasite Taenia solium (T. solium). The only animal reservoirs for this parasite are humans and pigs, it is transmitted from both by the oral-fecal route. The eggs enter our system via the consumption of either undercooked pork or water or vegetables that are contaminated by the stool of either animal. Under the influence of the acids and enzymes in our stomach the egg – a semitransparent, opalescent white, elongate oval in shape, and 0.6–1.8cm long – dissolves and releases the embryos, the cysticerci, which once into the intestine can grow into an adult tapeworm or travel by the blood to invade and infect other tissues in the body – typically the brain, muscle, skin, and eyes. Those that mature into adult tapeworms in the intestines and release gravid segments called proglottids which then exit the body via the stool discharging new eggs. When pigs and humans ultimately digest when those embryonated eggs the cycle starts anew.
Neurocysticercosis specifically refers to cysticerci within brain tissue. This is actually the most common site for the larvae to land and they can live there for 5-30 years before becoming symptomatic. They can cause seizures; block the outflow of cerebrospinal fluid; increased intracranial pressure; grow into large lobulated masses that put pressure on surrounding organs; and even get into the spinal cord and cause back pain and radiculopathy like in our patient here. Our patients MRI of his cervical spine showed smaller similar lesions in his cervical spine compressing his 5th and 6th cervical nerve roots. He is currently responding well to a regimen of praziquantel, albendazole, prednisone, and Dilantin.
Tapeworm infection and subsequent health problems are not a new phenomenon. The earliest reference to tapeworms were found in the works of the ancient Egyptians that date back to almost 2000BC. The description of ‘measled pork’ in the History of Animals written by Aristotle (384–322BC) showed that the infection of pork with tapeworm was known to ancient Greeks at that time. It was also known to Jewish and later to early Muslim physicians and has been proposed as one of the reasons for pork being forbidden by both Jewish and Islamic dietary laws. Recent examination of the evolutionary histories of hosts and parasites and DNA evidence show that over 10,000 years ago, ancestors of modern humans in Africa became exposed to tapeworm when they scavenged for food or preyed on antelopes and bovids, and later passed the infection on to domestic animals such as pigs.
This is not uncommon in the developing world and probably more common than you might think here in the US. In Latin America an estimated 75 million people live in endemic areas and of those 400,000 people have symptomatic disease. Some studies suggest that the prevalence of cysticercosis in Mexico is between 3.1 and 3.9 percent. Other studies have found that in impoverished areas of Guatemala, Bolivia, and Peru it’s as high as 20 percent in humans and 37 percent in pigs. In Madagascar 16% of the population is infected while in Ethiopia, Kenya and the Democratic Republic of Congo it’s around 10%.
The distribution of cysticercosis coincides with the distribution of T. solium. Worldwide cysticercosis is the most common cause of symptomatic epilepsy. Prevalence rates in the United States have shown immigrants from Mexico, Central and South America, and Southeast Asia account for most of the domestic cases of cysticercosis. In 1990 and 1991, four unrelated members of an Orthodox Jewish Community in New York City developed developed recurrent seizures and brain lesions which were found to have been caused by T. solium. All of the families had housekeepers from Latin American countries and were suspected to be source of the infections.
Deaths from cysticercosis worldwide increased from 700 in 1990 to 1,200 in 2010. In the US 221 cysticercosis deaths were identified from 1990-2002. Mortality rates were highest for Latinos and men. The mean age at death was 40.5 years. Most patients, 84.6%, were foreign born, and 62% had emigrated from Mexico. The 33 US-born persons who died of cysticercosis represented 15% of all cysticercosis-related deaths. The cysticercosis mortality rate was highest in California, which accounted for 60% of all cysticercosis deaths.