History of research on vector transmission

Throughout history people have speculated about an association between bloodsucking arthropods and illness. However, the involvement of arthropods in disseminating disease was demonstrated first only about 100 years ago. One of the earliest references to a role for arthropods in disease comes from the 16th century Italian physician Mercurialis, who hypothesized that by feeding on bodily secretions of dying persons, flies transmitted plague by depositing it into human food with their excretions (James & Harwood, 1969; Riley & Johannsen, 1915). Although we now know that this is not the mode of plague transmission, Mercurialis' speculation on a role for flies in mechanical transmission of pathogens was correct. Surprisingly, his observations pre-date van Leeuwenhoek's development of the microscope and his 1676 report of 'animalculus', now thought to have been bacteria in his aqueous samples.

The golden age of medical entomology began in the latter half of the 19th century. In 1848, Josiah Nott suggested that the causes of yellow fever and malaria existed in some form of insect life (Nott, 1848). Around the same time, the French physician

Table 1. Mechanism of pathogen transmission by arthropod vectors

Adapted from Edman (2000).

Transmission category Specific route of transmission Pathogen/vector

Vertical

Transovarial (mother to offspring)

Transstadial (stage to stage)

Venereal (male to female)

Co-feeding

Salivation

Stercorarian

Regurgitation

Assisted escape/passive transfer Active escape/invasion Ingestion by host

Babesia bigemina/tick Borrelia burgdorferi/tick La Crosse virus/mosquito Borrelia burgdorferi/tick Plasmodium spp./mosquito Trypanosoma cruzi/triatomid bug Yersinia pestis/flea Borrelia recurrentis/louse Onchocerca spp./black fly Dipylidium caninum/flea

Vertical

Horizontal

Horizontal

Horizontal

Horizontal

Horizontal

Horizontal

Horizontal

Horizontal

Beauperthuy suggested that yellow fever and other diseases are transmitted by mosquitoes (Beauperthuy, 1854; Philip & Rozeboom, 1973). In his 1909 review, Boyce called Beauperthuy the father of the doctrine of insect-borne disease. In 1877, Louis Pasteur, after much study of thus far invisible organisms, formulated his 'germ theory'. However, it was not until 1878 that irrefutable evidence of the role for arthropods as vectors of pathogens was established. In the first discovery of primary importance in medical entomology, Manson reported development of the filarial worm Wuchereria bancrofti in the mosquito Culex fatigans (now called Culex pipiens) (Manson, 1878). A series of discoveries further implicating arthropods in dissemination of disease immediately followed Manson's landmark work. Of major significance were: (1) the demonstration that Texas cattle fever is transmitted by the tick Boophilus annulata (Smith & Kilbourne, 1893); (2) malaria parasite development in and transmission by mosquitoes (Grassi et al., 1899; Philip & Rozeboom, 1973; Ross, 1897, 1898); and (3) the 1900 report by Reed and colleagues of yellow fever virus (YFV) transmission by Aedes aegypti (Philip & Rozeboom, 1973).

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