Mosquito host‐feeding patterns and implications for Japanese encephalitis virus transmission in northern Australia and Papua New Guinea

Abstract

Japanese encephalitis (JE) virus spread to northern Australia during the 1990s, transmitted by Culex annulirostris Skuse and other mosquitoes (Diptera: Culicidae). To determine the relative importance of various hosts for potential vectors of JE virus, we investigated the host-feeding patterns of mosquitoes in northern Australia and Western Province of Papua New Guinea, with particular attention to pigs, Sus scrofa L. - the main amplifying host of JE virus in South-east Asia. Mosquitoes were collected by CDC light traps baited with dry ice and 1-octen-3-ol, run 16.00-08.00 hours, mostly set away from human habitations, if possible in places frequented by feral pigs. Bloodmeals of 2569 mosquitoes, representing 15 species, were identified by gel diffusion assay. All species had fed mostly on mammals: only <10% of bloodmeals were from birds. The predominant species was Cx. annulirostris (88%), with relatively few (4.4%) bloodmeals obtained from humans. From all 12 locations sampled, the mean proportion of Cx. annulirostris fed on pigs (9.1%) was considerably lower than fed on other animals (90.9%). Highest rates of pig-fed mosquitoes (>30%) were trapped where domestic pigs were kept close to human habitation. From seven of eight locations on the Australian mainland, the majority of Cx. annulirostris had obtained their bloodmeals from marsupials, probably the Agile wallaby Macropus agilis (Gould). Overall proportions of mosquito bloodmeals identified as marsupial were 60% from the Gulf Plains region of Australia, 78% from the Cape York Peninsula and 64% from the Daru area of Papua New Guinea. Thus, despite the abundance of feral pigs in northern Australia, our findings suggest that marsupials divert host-seeking Cx. annulirostris away from pigs. As marsupials are poor JE virus hosts, the prevalence of marsupials may impede the establishment of JE virus in Australia.

North American Birds as Potential Amplifying Hosts of Japanese Encephalitis Virus

“…5,13,15,27 Characterization of avian host species responses to JEV infection is important in consideration of other variables that affect transmission dynamics, such as vector feeding preferences, vector and host densities, host behaviors, and ecological factors such as habitat and climate. 23 Differences in JEV viremia profiles among a variety of avian species, including numerous ardeids, were observed in the present and past studies, suggesting that reservoir competence varies among taxa 6,7,27 ; previous studies most often quantified viremia titers by the lethal viral dose in 50% of intracerebrally inoculated mice (LD 50 ). The majority of experimentally inoculated (Japanese JEV strain) rufous night herons (Nycticorax caledonicus) and plumed egrets (Egretta intermedia) had low level, sometimes intermittent viremia titers between 1 and 5 DPI, whereas smaller proportions of black-crowned night herons (N. nycticorax) and little egrets (Egretta garzetta) became viremic.…”

“…21,22 The presence of high numbers of JEV-competent vectors that ecologically overlap and preferentially feed on available, amplifying hosts in non-endemic areas would facilitate virus establishment and spread. 2,23 Laboratory studies suggest that some aspects of North American mosquito (Culex spp., Aedes spp., and Culiseta spp.) biology could support JEV transmission.…”

Change in Japanese Encephalitis Virus Distribution,Thailand

“…Some researchers (10) consider the increase of the virus incidence in the human population to be associated with increased commercial activity. However, because of the low level of viremia in humans, traditionally considered dead-end hosts for JEV, it is more likely that the virus was spread within the country and to neighboring countries by migratory birds, infected domestic pigs, or infected mosquitoes (or their eggs) (11,12).…”

Blood Sources of Mosquitoes Collected from Urban and Peri-Urban Environments in Eastern Australia with Species-Specific Molecular Analysis of Avian Blood Meals

“…Previous studies have examined the host-feeding patterns and host preference of Australian mosquitoes. [7][8][9][10] However, most of these studies have examined mosquitoes collected from remote and/or rural environments, and only a few have investigated common mosquitoes in the urban environment. 8 If one considers that 68.5% of the Australian population resides in major urban cities (with most persons concentrated on the east coast), 11 it is pertinent to examine host-feeding behavior in these habitats/environments.…”

“…Previous studies of host-feeding patterns in Australia have used immunologic assays, including gel diffusion 8,10 and precipitin tests. 7,14,15 Although these studies have generated critical epidemiologic information, serologic techniques are limited by availability of antisera against target species and the crossreactivity between serum proteins from closely-related species.…”