At one time bancroftian filariasis (Wuchereria bancrofti) was endemic in limited areas of the southern USA. Chernin (1987) suggested the hypothesis that bancroftian filariasis, which had been endemic since the early days of slavery in Charleston, South Carolina, disappeared around 1930 by virtue of the long-term effects of a municipal sewerage-water system begun in the 1890s or thereabouts. These public works, originally intended to abate typhoid and related diseases, helped to eliminate filariasis by reducing the availability of polluted domestic waters which are the preferred breeding sites for the urban vector, Culex quinquefasciatus. With the disappearance of this focus, the only filarial infection of man in the USA is the occasional case of dirofilariasis.

Canine heartworm disease is transmitted by mosquitoes and results from parasitization by the filariid worm Dirofilaria immitis. While presenting some danger to humans, the filariid has its greatest impact on canine populations and, to a much lesser extent, on feline populations. It is a potentially fatal infection in both dogs and cats. In recent years the disease has become established throughout much of the USA and part of Canada. Both D. immitis and D. repens, also found in dogs and cats, are found in Europe but in the USA the causative agents of human dirofilariasis may be D. immitis and D. tenuis; the natural hosts of the latter species are raccoons (Procton lotor) and opossums (Didelphis species).