Identification of the source of blood meals in mosquitoes collected from north-eastern Australia

Abstract

Background: More than 70 arboviruses have been identified in Australia and the transmission cycles of most are poorly understood. While there is an extensive list of arthropods from which these viruses have been recovered, far less is known about the non-human hosts that may be involved in the transmission cycles of these viruses and the relative roles of different mosquito species in cycles of transmission involving different hosts. Some of the highest rates of human infection with zoonotic arboviruses, such as Ross River (RRV) and Barmah Forest viruses (BFV), occur in coastal regions of north-eastern Australia. Methods: Blood-engorged mosquitoes collected as a part of routine surveillance using CO2-baited light traps in the Rockhampton region and the adjoining Shire of Livingstone in central Queensland, north-eastern Australia, were analysed individually for the source of their blood meal. A 457 nucleotide region of the cytochrome b gene of blood in engorged mosquitoes was amplified by PCR and the amplicons sequenced. The origin of the blood were identified by comparing the sequences with those published in the GenBank. Results: The most common hosts for the mosquitoes sampled were domestic cattle (26/54) and wild birds (14/54). Humans (2/54) were an infrequent host for this range of mosquitoes that are known to transmit arboviruses causing human disease, and in an area where infections with human pathogens like RRV and BFV are commonly recorded. The blood meals identified in the most abundant vector analysed, Culex annulirostris, were from 10 different vertebrate hosts. The notable detection of chimpanzee blood in two mosquitoes, presumably obtained from a nearby zoo, extends the known range of hosts for this species. Culex quinquefasciatus and Cx. sitiens fed almost exclusively on a variety of bird species. Conclusions: While human-mosquito-human transmission of arboviruses like RRV can occur this study highlights the potential importance of zoonotic cycles of transmission including avian species, of arboviruses that are indigenous to Australia. Further work on larger samples of blood-engorged mosquitoes is required to validate the trends observed herein as well as to confirm the virus isolations from the various vertebrate hosts that have been identified in this study