Abstracts and Reports Potential Eradicability of Taeniasis and Cysticercosisl

s and Reports Potential Eradicability of Taeniasis and Cysticercosisl P.M. SCHANTZ,~ M. CRUZ,~ E. SARTI,~ & Z. PAWLOWSKI~ THE PROBLEM Biology and Transmission Taeniasis and cysticercosis, respectively, are infections with the adult and larva1 stages of tapeworm parasites belonging to the genus Taenia. The two taeniid species that commonly infect humans, T. solium and T. saginafa, both require two hosts to complete their life cycles. Human beings are the obligatory final hosts of both species’ adult-stage tapeworms, while swine and cattle are the natural intermediate hosts for the larval-stage parasites (cysticerci) of T. solium and T. saginata, respectively. In many regions of the world T. solium taeniasis/ cysticercosis is an important health problem of man. In addition, both tapeworm species cause livestock infections responsible for serious economic losses. ‘Adapted from a presentation at the Fifth Meeting of the International Task Force for Disease Eradication, Washington, D.C., March 1992. This contribution will also be published in Spanish in the Boletin de la Oficina Sanitaria Panamericana, Vol. 116, No. 6. Humans acquire intestinal tapeworm infections (taeniasis) by ingesting cysticerci in raw or inadequately cooked meat (pork or beef) of infected intermediate hosts. Two to three months later, mature tapeworms that have grown to a length of several meters make daily releases of gravid segments containing many thousands of infective eggs into the human host’s stools. The intermediate animal hosts acquire cysticercosis by ingesting taeniid eggs passed in stools of the human tapeworm carriers. These eggs hatch into embryonic parasites within the animals’ intestines and develop into larval cysticerci in their muscles and other tissues. The egg stages of T. s&urn (but not T. saginata) can also infect humans, and in this way can give people potentially life-threatening neurocysticercosis. For that reason, the medical importance of infection with T. solium is much greater than infection with T. saginata. 2Division of Parasitic Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia, United States. 3Ecuadorian Academy of Neurosciences, Ramirez Davalos 136, Quito, Ecuador. 4Directorate of Epidemiology, Secretariat of Health, Mexico City, Mexico. Uinic of Parasitic and Tropical Diseases, University School of Medicine, Poznan, Poland. Medical and Veterinary Impact Tapeworm infection of the human intestine by either T. sodium or T. saginata may cause abdominal pain, anorexia, and other gastrointestinal symptoms but is Bulletin of PAHO 27(4, 1993 397 rarely of serious medical consequence. In contrast, T. sodium cysticercosis in humans, which is often symptomatic, can produce severe or fatal results. Although larval parasites may localize throughout the human body, most clinical manifestations are related to the presence of cysticerci in the central nervous system (neurocysticercosis), where they may invade the parenchyma, subarachnoid spaces, and ventricular system and cause seizures, hydrocephalus, focal neurologic signs, and psychiatric disorders involving physical and/or mental disability with a high risk of death (see photo, below). Cysticercosis in animal intermediate hosts rarely causes clinical impairment of growth and production; however, the market value of infected meat is greatly reduced. Prevalence and Distribution Although T. sodium and T. suginata infections occur throughout the world, the prevalence of both species is highest in rural areas of Latin America, Asia, and Africa. Environmental conditions common to most communities where taeniasis and cysticercosis are endemic include inadequate mechanisms for disposing of human feces together with swine and cattle husbandry practices that give those livestock access to such feces (see photo, p. 399). Taenia infections are generally underdiagnosed and underreported. However, the World Health Organization has estimated that these infections afflict some 50 million people and kill roughly 50 000 human beings a year. The total numbers Cross-section of the brain of a g-year-old Mexican girl who died of complications associated with massive cerebral cysticercosis. (Photo courtesy of Dr. Ana Flisser.) 398 Bulletin of PAHO 27(4), 1993 do not distinguish between 7’. s&urn and T. saginata infections, but it may be assumed that virtually all the deaths are due to T. solium neurocysticercosis. Most statistics on morbidity and mortality caused by neurocysticercosis are clinic-based. In Mexico, South Africa, and other countries where such data have been recorded, it has been found that neurocysticercosis is a common cause of death in neurosurgical services, the usual cause of late-onset epilepsy, and the cause of death or an incidental finding in 2% to 4% of all autopsies. Rural community-based surveys, carried out recently in Mexico and Togo, indicate that rates of epilepsy are three to four times higher in the survey areas than in industrialized countries, and serologic evidence implicates neurocysticercosis as the cause of at least 25% to 33% of the cases. During the 198Os, the incidence of infection indicated by clinical diagnoses increased markedly as a result of improvements in radiologic and serologic diagnostic methods. Besides being observed in developing areas, this apparent increase was also found in industrialized countries-including the United States, where most cases are imported. Economic losses caused by swine and cattle cysticercosis, although estimated for only a few countries, impose significant The outside commons area of a household in a region of Mexico where Taenia so/km is endemic. The unrestrained sow and piglets have access to human fecal wastes deposited on the open ground or in shallow pit latrines. Abstracts and Reports 399s and Reports 399 burdens on livestock industries. In Mexico, porcine cysticercosis is responsible for loss of more than half the national investment in swine production, and in Latin America generally it has been estimated to impose an annual economic loss of roughly US$ 164 million. In Africa, losses of US$ 1 000-2 000 million have been attributed to bovine cysticercosis. The near impossibility of keeping livestock free of infection under prevailing conditions continues to frustrate the development of a profitable cattle industry in many developing countries. THE CASE FOR ERADICATION The following characteristics of T. suZium and T. saginata infections make them vulnerable to eradication: (1) the life cycles require humans as definitive hosts; (2) tapeworm infection in humans is the only source of infection for intermediate hosts; (3) domestic animal intermediate-host populations can be managed; (4) no significant wildlife reservoirs exist; and (5) practical intervention is available in the form of mass chemotherapy of human taeniasis with safe and effective drugs. Because of marked differences in the population stability of the two species, however, T. suginatu appears much harder to eradicate than T. s&urn. Indeed, the prevalence of T. saginatn has increased in Europe over the past 40 years. For example, the prevalence of bovine cysticercosis in Germany before 1950 was reported at around 0.3%, while at present it is reported around 2% and may be higher in some regions. This increasing bovine cysticercosis incidence appears associated with intensification of cattlerearing operations, limited ability to detect infected carcasses through meat inspection, increased movement of people from T. suginatu-endemic areas for reasons of tourism and immigration, increased popularity of raw beef dishes, and sewage treatment facilities’ inability to destroy taeniid eggs. For all these reasons, new knowledge, tools, and intervention strategies are needed to effectively control bovine (T. suginata) taeniasis and cysticercosis. In contrast, T. solium taeniasislcysticercosis appears to be a good candidate for eradication because it has gradually disappeared from most European countries even in the absence of specifically targeted control measures. At the end of the last century, the prevalence of T. solium in swine and humans in Germany was similar to that found today in Mexico and other endemic regions. However, the occurrence of T. solium in Europe is now limited to scattered foci in eastern and southern Europe. Factors credited with the elimination of T. soIium include improvements in general sanitation and economic status, the introduction of indoor swine husbandry, and rigorous meat inspection. The reasons why the first and third of these factors have not also reduced or eliminated the transmission of T. suginatu may be related to different characteristics of the cattle and swine husbandry systems and different feed sources for these animals.