Operational Trials of Remote Mosquito Trap Systems for Japanese Encephalitis Virus Surveillance in the Torres Strait, Australia

Abstract

Japanese encephalitis virus (JEV) appears nearly annually in the Torres Strait in far northern Queensland, Australia, and is a threat to invade the Australian mainland. Surveillance has involved the use of sentinel pigs that develop detectable viremias and antibody titers to JEV. However, pigs are amplifying hosts for JEV, and thus pose a health risk to the public and to pig handlers who bleed the pigs. A remote mosquito trap system would not have these risks. We report on trials using a remote mosquito trap system for the surveillance of JEV in the Torres Strait. The Mosquito Magnet (MM) Pro, MM Liberty Plus, and a novel updraft trap, the NAQS Mozzie Trap, were run at Badu and Moa islands in the Torres Strait and at Bamaga in the northern Cape York Peninsula from 2002-2005. TaqMan real-time polymerase chain reaction (PCR) was used to detect JEV nucleic acid in weekly mosquito collections. Sentinel pigs located at Badu were also bled and the serum processed by reverse transcriptase (RT)-PCR for JEV antigen and enzyme-linked immunosorbent assay (ELISA) for anti-JEV antibodies. JEV was detected in mosquito collections each year but not in each trap. No JEV was detected in trapped mosquitoes before detection in sentinel pigs. The mosquito trap system cost ca. AU$10,000 per site, about AU$5,000 less than a pig-based system. However, trap failures caused by mosquito-clogged motors, electrical faults, and blocked gas lines reduced the efficacy of some mosquito traps. Nonetheless, a remote mosquito trap system, employing stand alone traps and PCR for viral antigen detection, can be a safe, economical way to detect arbovirus activity in remote areas.

Exploiting mosquito sugar feeding to detect mosquito-borne pathogens

“…For instance, disease surveillance systems are hampered by a similarity of disease signs and symptoms induced by different pathogens, the potentially low clinical to subclinical disease ratio, and the recognition of cases only after an outbreak has commenced. The disadvantages of sentinel animals include the need for intensive animal husbandry and risk of injury to staff bleeding animals (7). Furthermore, sentinel animals may themselves be amplifying hosts of the virus, thus contributing to the transmission cycle, and some closely related arboviruses are difficult to distinguish using current serological tests.…”

“…Furthermore, sentinel animals may themselves be amplifying hosts of the virus, thus contributing to the transmission cycle, and some closely related arboviruses are difficult to distinguish using current serological tests. Finally, processing thousands of mosquitoes for virus detection is labor-intensive, especially when presorting of mosquitoes is required, and often requires a cold-chain to preserve viral integrity in arthropods collected from the field (7).…”

Evolution of Mosquito-Based Arbovirus Surveillance Systems in Australia

“…Between 2001 and 2005, a field trial was conducted in the Torres Strait and northern Cape York Peninsula with the objective of comparing the mosquito-based surveillance system with the sentinel pig programme [29]. Weekly mosquito collections from either the Mosquito Magnet and/or the Northern Australian Quarantine Strategy Mozzie Trap (NMT; 29), a trap developed for the purposes of long term deployment, were submitted for detection of JEV RNA.…”

Japanese Encephalitis: An Emerging and Spreading Arbovirosis

“…Sentinel pigs have a tendency to develop detectable viremias to JEV. Since pigs are amplifying hosts for JEV, they are health risk to the public (Ritchie et al, 2007. Culex mosquitoes in Cape Town (van den Hurk et al, 2006) and Saibai Islands may be responsible for JEV activity (Johansen et al, 2004).…”