Perhaps the best known aspect of the importance of parasites is the role that they play in causing human disease. For example, hundreds of millions of people suffer from malaria, and each year over one million human deaths are caused by this parasitic disease. Diseases caused by many species of parasitic worms, such as blood flukes, tapeworms, hookworms, and others are still scourges of mankind. Insect parasites such as fleas and lice are, at best, annoyances to man, and as vectors of diseases like bubonic plague and typhus have been responsible for uncountable human mortality. Mosquitoes not only transmit malaria, but spread yellow fever, encephalitis, and other viral diseases, and are responsible for inoculating into humans several species of filarial worms that cause some of the most horrific diseases in the medical literature. Emerging diseases such as Lyme disease, transmitted by ticks, are increasingly recognized as significant to human health. Medical parasitologists utilize many approaches in combating parasites. Among the areas of research are epidemiology, chemotherapy, immunology, and pathology.
Exciting advances that hold promise in reducing parasitic disease have come from basic research by parasitologists in the fields of molecular and cellular biology, genetics, and physiology. Promising breakthroughs in the development of vaccines against medically important parasites exist because of technological and conceptual advances in these fields, as well as in allied disciplines like immunology, vector biology, and biochemistry. The field of public health is closely allied with medical parasitology. The global distribution of parasites offers great challenges to workers in this field. Public health practitioners are employed by national, state, and local governments, or may work for international agencies like the World Health Organization. Private industry, philanthropic and charitable organizations, military organizations, and a variety of other institutions also utilize the services of workers in the area of public health.