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Mosquito Research

Living in Far North Queensland, residents know what a nuisance mosquitoes can be. Consumer demand for mosquito traps that can be used around the home led to the development of a new trap called the 'Mega-Catch' invented by Envirosafe Technologies. To see how its performance compared with other designs, the Dr Edward Koch Foundation conducted large-scale mosquito trapping in Cairns. Our study site was the Cairns Waste Transfer Facility at Smithfield, where we trapped for 12 nights. There was no shortage of mosquitoes. By analysing our bounty of over 110,000 mossies, we were able to rank the 12 different trap designs in terms of performance, the most effective of which was the 'Mega-Catch' traps.

Banks Mosquito Trap

From the Desk of Dr Scott Ritchie. The last few months have been very productive for the Tropical Public Health Unit (TPHU) medical entomology team. Firstly, we have eliminated a large outbreak of dengue in Cairns. Secondly, work sponsored by the Dr Edward Koch Foundation has paid handsome dividends.

A project funded by Australia Biosecurity, through the Foundation, has confirmed that a new type of mosquito trap catches nearly seven times as many JE mosquitoes as the traditional mosquito trap. Dr David Banks of Australian Biosecurity developed an updraft mosquito trap that incorporates a fan, a CO2 cylinder and a solar-powered 12 volt battery to collect mosquitoes.

The CO2 attracts mosquitoes, much like your breath, which is composed of CO2, draws them to you. While there are many such mosquito traps on the market, the Banks trap differs by using a powerful fan to suck the mosquito up into a collection cage using an updraft of air situated just above the CO2 gas. Mosquitoes, when they feel that they are being "swept away", engage in evasive action by flying up, right into the updraft and into our collection cage. Most traps use downdraft fans, and thus are fighting against mosquito urges to fly away.

In trials conducted in Cairns recently by Ian Walsh of the TPHU and Paul Zborowski (funded by the Dr Edward Koch Foundation), this trap collected nearly seven times as many Japanese encephalitis mosquitoes as the standard mosquito trap. This year, we will trial the Banks trap in the Torres Strait as a new system to monitor for Japanese Encephalitis in Australia.

Banks mosquito trap, solar panel and carbon-dioxide supply

I have also been conducting research with the staff of the National Institute of Hygiene and Epidemiology (NIHE) in Vietnam in a project partially funded by the Dr Edward Koch Foundation. The sticky ovitrap, developed at the TPHU, consists of a 1.2 litre plastic bucket containing 500 ml of stagnant water.

Dengue mosquitoes, looking for a container of water to lay their eggs in, are attracted to the bucket. But inside, we have placed a plastic strip containing a powerful adhesive that catches the unwary mosquito. We set sticky ovitraps in a Vietnamese village not far from Hanoi, with the aid of Tessa Knox, a PhD student of the Queensland Institute of Medical Research, and the staff of NIHE.

Large numbers of Asian tiger mosquitos (Aedes albopictus,) were collected, along with some dengue mosquitoes (Aedes aegypti). Because the Asian tiger mosquito is not currently found in Australia, Australian Quarantine and Inspection Services (AQIS) carefully monitors for its presence at all Australian ports.

Our results clearly demonstrate that the sticky ovitrap is an excellent way to monitor for this high risk mosquito. Under the guidance of Professor Vu Sinh Nam of NIHE, director of the dengue control program in Vietnam, I have been shown the highly successful and novel dengue control program.

This program, initiated in collaboration with Professor Brian Kay of QIMR, utilises small shrimp-like planktonic animals called copepods to ingest newly hatched mosquito larvae. The copepods are reared at NIHE’s lab then posted on moist sponges to district health offices. Health officials then distribute the "mosquito-bomb" sponges to villages where a small sponge cube is dropped into rainwater tanks. Within weeks, no mosquitoes. The program was shown to me in a small village in NW Vietnam. We sampled many water tanks, finding no mosquito larvae but plenty of copepods. So far, dengue has been eliminated from these villages.

Pig's Days are Numbered for Japanese Encephalitis Surveillance

Dr Edward Koch Foundation has sponsored several studies on mosquito-borne diseases. In addition to former mosquito repellent trials, members of he Tropical Public Health Unit's Medical Entomology section in collaboration with the Foundation have conducted studies designed to improve our ability to monitor for Japanese encephalitis (JE) in the Torres Strait and Cape York. This project, funded by Australian Biosecurity and Australian Quarantine and Inspection Services (AQIS), field tested the use of stand alone mosquito traps to detect JE virus in mosquitoes.

Japanese encephalitis virus remains an annual threat to northern Australia, especially in the Torres Strait and Cape York. AQIS currently deploy three herds of sentinel pigs at Badu Island, Bamaga, and Normanton to monitor for incursions of JE. However, the pigs, while effective, do pose problems. They are expensive, logistically difficult to establish, pose a risk to staff who bleed them and, most importantly, are a public health risk as they can amplify JE virus. AQIS has listed the development of new surveillance methods, including the use of sentinel mosquito traps, as a high priority.

The development of a sentinel mosquito trap for the detection of JE has proceeded rapidly. First, our lab demonstrated that a stand alone mosquito trap, the MosquitoMagnet (MM), collected large number of the target mosquitoes. This established that a stand alone trap that used propane could be used to collect mosquitoes with servicing on a weekly basis. A pilot field project demonstrated that a single infected mosquito housed for up to 2 weeks in a MosquitoMagnet could be detected in pools of up to 5000 mosquitoes using the PCR technology by Alyssa Pyke and Greg Smith of QH Scientific Services lab in Brisbane. In fact, we detected JE viral RNA by PCR in a pool of 1000 mosquitoes collected by a MM trap set adjacent to the Badu Island piggery in March 2002. Paul Zborowski has been employed to sort the thousands of mosquitoes collected by the traps.

These developments clearly indicate that a sentinel mosquito trap system can collect mosquitoes in remote areas that can be subsequently processed for JE RNA using the Taqman PCR. Dr Koch is currently sponsoring an operational field trial of a sentinel mosquito trap system to detect JE virus in the Torres Strait in the upcoming wet season. To date the project has been successful. Three separate mosquito collections have been positive for JE virus in MosquitoMagnet traps set on Badu and in St Pauls on Moa Island. Clearly, this study indicates that the days of sentinel pigs may indeed be numbered in the Torres Strait and Cape York.

The Tropical Public Health Unit's Brian Montgomery starts up a MosquitoMagnet in the fight against Japanese encephalitis in the Torres Strait.

New Mosquito Repellents

The Dr Edward Koch Foundation has funded research by an American company in the search for better repellents. Dr. Koch will help fund research into novel repellents and mosquito traps. "They like to work in Australia because they can continue to get field trials conducted during the northern winter." Dr. Ritchie headed a team that recently conducted a repellent trial for FMC Corp near Palm Cove. The new repellent is a botanical derived from the leaves of a plant with suspected mosquito repellent action. "We literally bare our legs to the mosquitoes!". Dr. Ritchie said. "People would ask 'why is your pant leg up?' To which we repied 'It's a cult.' " The product should do nicely in California.

Dengue Fever Field Trial

Dr Scott Ritchie, Medical Entomologist at the Tropical Public Health Unit, Qld Health was the principal investigator in a research project aimed at testing the efficacy of household insecticides against the Aides Egypti mosquito, the carrier of dengue fever.

The study involved collecting mosquitoes inside the house using a vacuum aspirator. For houses where mosquitoes were collected, a second collection was made within a week.

Homeowners were then given either bug zappers or a can of fly spray, along with instructions for their use. Within a day, resampling for mosquitoes was done to see if the insecticide was effective.

Residents of North Queensland are particularly at risk because of the climate and the increasing number of visitors who have travelled in countries where dengue fever occurs.

Thus, the Foundation is committed to ensuring that the virus is not spread by using prevention as the best protection against mosquito borne diseases.

OCHLEROTATUS VIGILAX, CERATOPOGONIDAE AND OTHER NASTIES

Dr. Scott Ritchie and his team continue their research on the above-mentioned insects - known to most people as those irritating, biting saltmarsh mosquitoes and sandflies. He and his team recently conducted a study on behalf of the Foundation on the efficacy of VMart Mosquito and Fly Traps, designed for use in home, both inside and out and for camping. The traps emit both carbon dioxide and UV light, which attract the insects.

Comparisons were made between two photo-catalyst mosquito light traps from VMart and the BG-Sentinel mosquito trap which is currently used by Queensland Health and James Cook University for research into dengue mosquitoes. The traps were set in urban suburbs in Cairns.

Both VMart Traps collected useful numbers of mosquitoes and significantly, large numbers of female mosquitoes. It is only the females of the species that bite and take blood. Large numbers of nuisance mosquitoes such as the saltmarsh Oc. Vigilax were collected in the VMart traps, indicating that the UV light used in these traps is highly attractive to these mosquitoes. Carbon dioxide generated by a titanium oxide plate in the trap could also have attracted them. The trial did indicate that many nuisance insects were attracted to the traps, but unfortunately Dr. Ritchie does point out that the trial did not test if the use of the mosquito traps would decrease biting by mosquitoes and sandflies. Such a trial would require human volunteers, ethical approval, and be more costly.

The Foundation collaborated in a project with the Australian Biosecurity Cooperative Research Centre to finalise a mosquito trap for the surveillance of Japanese encephalitis (JE) in Australia. JE is a disease carried by mosquitoes that first appeared in this country in 1995, killing two people on Badu Island in the Torres Strait. Australian Quarantine and Inspection Services (AQIS) in collaboration with Queensland Health use small herds of sentinel pigs placed in the Torres Strait islands and the tip of Cape York to monitor the presence of JE. The pigs are bled weekly and tested for the virus, but the pigs can themselves help spread the virus.

Dr Ritchie's team has been testing a new system to replace the pigs, using traps to collect mosquitoes that are tested for the JE virus. Mr Joe Davis was recently employed by the Dr Edward Koch Foundation to conduct a field trial of a new updraft mosquito trap. The trap proved to be very effective, catching three times as many mosquitoes as the standard trap, and providing a constant wind flow to prevent mould from destroying the mosquitoes. Dr Ritchie is using the new trap in field trials in the Cairns area, and is hoping to use it in remote areas in the wet season.