ABSTRACT
Trichinellosis is a human disease caused by the larvae of several roundworm species within the genus Trichinella. There are at least eight species of Trichinella, but most human disease is the result of T. spiralis: a pathogen that now occurs around the world due to humans inadvertently moving infected pigs around the world. Animals and humans are infected by consuming meat containing the encysted larvae of Trichinella (Figure 29.1). Once ingested, the digestive enzymes in the stomach dissolve the capsule surrounding the larvae, freeing them to burrow into the cells lining the intestines. Once there, the larvae grow quickly and become adults of about 0.1 in. (3 mm) within a week (Figure 29.2). Females start producing live larvae as soon as they become adults. Most adult roundworms do not survive for more than 4 weeks before they are killed by the host’s immune system; however by then, each adult female can produce between 500 and 1500 live larvae (Figures 29.3). These second-generation larvae are not shed in feces but instead burrow through the cells of the intestine and are swept into lymphatic systems and bloodstream, which carries them throughout the body. They then burrow through the capillaries and into cells, seeking a striated muscle cell, which they need to survive. Larvae may select cells to invade at random, resulting in cell destruction. Once invaded by a larva, a muscle cell does not die but is altered by the larva into a nurse cell where the larva grows and encapsulates 18-20 days later. Once encapsulated, the larva can survive for months to years. If the infected animal or its carcass is consumed by a predator, omnivore, or scavenger, the encysted larva will complete its life cycle by infecting the digestive system of the new animal and maturing into an adult (Despommier 1990, Capó and Despommier 1996, Despommier et al. 2005).
