This review will focus on arthropod transmission to humans, giving a historical perspective of what is known with respect to the primary human vectors, hard ticks, flies and mosquitoes, focusing on species for which data exists to support their role as vectors in nature. Moreover, identification of the two type A clades, A1 and A2, both of which have been linked to vector-borne transmission, only occurred within the last five years. As a result, much of the older arthropod studies cannot be accurately interpreted with respect to the infecting strains. tularensis subspecies, type A and type B by Olsufiev in 1958. tularensis was last actively investigated in the time period from 1920 to 1955, prior to identification of the two F. Little, however, is known about the mechanisms important for adaptation of this organism to such a wide diversity of arthropod vectors. tularensis is endemic on different continents in differing ecologies, many variations occur in local transmission cycles. tularensis to varying vector, host and environmental conditions. tularensis to other susceptible hosts, including humans.įew pathogens show the adaptability of F. Some arthropods are also capable of transmitting F. tularensis infection within the host population. Ectoparasites likely play an important role in maintenance by disseminating F. tularensis subspecies, type A and type B, are associated with differing animal hosts type A is more commonly associated with lagomorphs (rabbits and hares), whereas type B is more frequently associated with rodents. Maintenance in nature is primarily associated with rodents and lagomorphs. tularensis is associated with a wider range of hosts than most other zoonotic pathogens natural infections have been found in > 100 species. If either form is not treated with appropriate antibiotics, secondary complications can arise, including suppuration and skin eruptions, and less commonly pneumonia and meningitis. Glandular tularemia is characterized by regional adenopathy without an identifiable skin ulcer. Ulceroglandular tularemia, the most common form associated with arthropod bite, is characterized by an ulcer at the site of the tick bite and enlargement of regional lymph nodes. Two primary disease manifestations, ulceroglandular and glandular, can arise from the bite of an infected vector. Vector-borne transmission of tularemia is now known to occur throughout the northern hemisphere, with varying degrees of frequency in differing geographic regions. tularensis was first isolated from ticks by Parker studying Dermacentor andersoni in Montana in 1924. Tick borne tularemia was recognized in 1923 by physicians in Idaho who noted enlargement of lymph nodes in response to a tick bite. In subsequent laboratory studies, Francis and Mayne confirmed transmission from infected to healthy animals by deer fly bite. Īrthropod-borne transmission of tularemia was first established by Francis in 1919 when he isolated the etiologic agent from a Utah patient with “deer fly fever”, an ulceroglandular condition described by Pearse in 1911. In the USA, A1 strains occur primarily in the eastern half of the country while A2 strains occur only in the west. Type A strains have been further divided into two genetically distinct subpopulations, A1 and A2, which differ with respect to clinical severity. Whereas type B infections occur throughout the northern hemisphere, type A infections are limited to North America. tularensis cause most human illness, subspecies tularensis, also known as type A, and subspecies holarctica, referred to as type B. The etiologic agent is Francisella tularensis, a gram-negative coccobacillus that is highly infectious and may be transmitted to humans by a number of different routes, including handling infected animals, ingestion of contaminated food or water, inhalation of infective aerosols and arthropod bites (ticks and insects). Tularemia is a bacterial zoonotic disease of the northern hemisphere.
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