Neurocysticercosis, the infection of the central nervous system with the cestode Taenia solium, is a major cause of acquired epilepsy and an important public health problem. This parasite has a two-host life cycle: humans are the definitive host that harbors the adult tapeworm, while both humans and pigs are intermediate hosts and harbor the cysticerci. This dissertation evaluates the clustering of human and porcine cysticercosis surrounding T. solium tapeworm carriers and discusses its implications for epidemiology and control.
This dissertation is presented in three papers. In the first, a short follow-up field study of T. solium cysticercosis and taeniasis, swine seropositivity clustered in hotspots around tapeworm carriers. Swine seroprevalence increased from 18% at >500m from carriers to 69% within 50m, and seroincidence increased from 4% at >500m to 44% within 50m. Pigs owned by carriers had four times more seroincidence than other pigs.
The second paper evaluated the aggregation of human cysticercosis seroprevalence and seizures around carriers. Seroprevalence increased closer to carriers from 21% >50m from carriers to 64% among tapeworm carriers and their families. Seizures, however, were not associated with the distance to the carrier.
Finally, the clustering of necropsy-confirmed viable swine cysticercosis infection around tapeworm carriers was evaluated. Viable infection prevalence formed a significant gradient going from 0.5% at >500m to 10.6% at 2-500m, and to 70.0% at the carriers' homes. Nearly all pigs with viable infection were within 500m of carriers.
The aggregation of viable swine infection and human and swine seropositivity around carriers provides an avenue to apply focused control measures inside transmission hotspots where both infected hosts can be reached. Increased risk was also present among carriers' neighbors and their neighbors' pigs, extending for up to hundreds of meters.
Many gaps remain in our knowledge of cysticercosis' transmission dynamics, such as egg dispersion mechanisms and their implications for disease transmission. With the promise of swine vaccines, the benefits derived of an improved understanding of T. solium epidemiology can be unappreciated. However, the limited impact of control measures call for caution about the success of future interventions until T. solium transmission dynamics are better understood.