Other mosquito-borne diseases

A sidebar to ‘Oxford and the mosquito’

By John Garth

Malaria may be the biggest killer riding shotgun on the mosquito, but it is certainly not the only one. The Oxford University Clinical Research Unit (OUCRU) in Ho Chi Minh City has a different priority — dengue fever.

Unlike its malaria-carrying cousin, the Aedes aegypti mosquito that mostly carries dengue is an urban creature. Aedes albopictus, another mosquito spreading dengue and perhaps Zika, has colonised widely in an unforeseen consequence of human ingenuity. You know the residual water that you can never shake out of the inside of a tyre because it just rolls around? The albopictus larvae thrive in it. In the 1960s dengue had almost been eradicated in Brazil but the spare tyre trade has led to a resurgence.

Most dengue patients suffer headache and fever, but a few undergo a catastrophic drop in blood-pressure known as ‘shock’, which can be fatal. For this virus-like illness there is no cure. Under Professor Guy Thwaites, the unit’s 400 staff across Vietnam, Nepal and Indonesia have been clinically trialling existing drugs for other conditions to see whether they have any effect against dengue. The prime focus meanwhile is on clinical management of dengue — in particular, working to establish the best level of fluid for patients.

The Vietnam unit is assisting with trials to reduce the mosquito’s ability to carry dengue, a project begun by former OUCRU researcher Professor Cameron Simmons. Insects infected with Wolbachia, a naturally occurring bacterium that prevents them from carrying the disease, have been released on a small scale on an island near Nha Trang, Vietnam. Much larger-scale Vietnam trials are planned.

‘Lots of care needs to be taken with this kind of approach,’ says Guy Thwaites, director of OUCRU in Ho Chi Minh City. ‘Biological control interventions have gone wrong in other very different settings — myxomatosis, and cane toads in northern Australia. So people are very wary of introducing biology against biology. But so far the experiments have been very promising, and certainly look to be safe, and the next step is to do big trials to show this intervention really has prospects for reducing this disease.’

Based at the Ho Chi Minh City Hospital for Tropical Diseases since 1991, OUCRU has also identified Zika virus in a significant minority of mosquitoes caught in its trapping programme.

Thwaites’ medics at OUCRU in South-East Asia also have to focus on clinical care in cases of Japanese encephalitis, carried by a different mosquito again. That disease occurs in epidemic proportions in the north of Vietnam but in smaller, yet persistent cycles in the south — and it affects young people and especially children. There are hopes, as well, that work on improving diagnosis of the condition will bear fruit.

In a truly multi-pronged attack, Thwaites wants to find ways to encourage the populations most vulnerable to Japanese encephalities to come forward for vaccination. That demands of his team not just skill in the lab and hospital, but also diplomacy and good communications. In dealings with national authorities, the Oxford track record on tropical diseases (not to mention the university’s internationally visible brand name per se) can ease the path.

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