The announcement of successful human trials of a vaccine against the Chikungunya virus is good news for travellers and those who live with the risk of the mosquito-borne virus across the tropical world.
Conducted by the US’ National Institute of Allergy and Infectious Diseases (NIAID), the Chikungunya vaccine trials involved 25 volunteers aged 18 to 50, who received three doses of varying strengths over 5 months.
Most had neutralising antibodies in their blood after the first dose and all 25 had them after the second dose. Antibodies were still present after 6 months, while after 11 months antibody levels were similar to those in people who had recovered after natural Chikungunya infection, suggesting that the vaccine could provide long-term protection.
Key trial results reported by the research team included:
- The vaccine generated antibodies against multiple Chikungunya genotypes, suggesting it will be effective against all strains of the virus. (In contrast, the most advanced dengue vaccine due to be released next year appears to offer only incomplete and variable protection across the 4 dengue virus serotypes.)
- It will be relatively economical to make in large quantities.
- The same technique could be used to produce vaccines against a range of encephalitis-causing viruses related to Chikungunya.
DRAMATIC RESURGENCE OF CHIKUNGUNYA
Like dengue fever, Chikungunya is spread by Ae. albopictus and Ae. aegypti mosquitoes, both aggressive daytime feeders that live close to humans.
The World Health Organisation reports a ‘dramatic resurgence and geographic extension of Chikungunya in recent years’.
In the last decade there have been large-scale outbreaks in East and Central Africa, and the nearby island nations of the Indian Ocean. In 2006, more than 1.25 million people in India and South Asia were infected in just 9 months, while in 2007 an unlikely outbreak occurred in northern Italy after the virus was ‘imported’ by a traveller.
This year the virus has swept the length and breadth of the Caribbean Basin, having now infected 585,798 people and claiming 37 lives in the past 8 months. The toll belies the notion that although Chikungunya causes fever and intensely painful arthritis, it is generally a benign illness.
In fact, few of those infected escape symptoms. As many as two-thirds of the population of some Caribbean islands have experienced the virus’ crippling pain, while the epidemic has also severely disrupted tourism, the lifeblood of the region’s economy.
VIRUS SPREADING TO AMERICAS, PACIFIC
The Caribbean epidemic showed signs of slowing in the past week, although the lower numbers may simply be due to a lack of reporting by many countries hurt by the decline in tourism revenue.
Meanwhile, both imported and local cases are increasing in neighbouring South and Central America countries, and in a growing number of southern US states. European authorities fear the Continent could be next, given the popularity of the Caribbean with European travellers and the presence of the Ae. albopictus mosquitoes that spread the virus in both Italy and France.
Chikungunya also reappeared in the Pacific in mid-July. After arriving in American Samoa – probably ‘imported’ from the Caribbean – it has generated an estimated 500 confirmed or suspected cases before ‘island-hopping’ to nearby Samoa for the first time less than a fortnight later, quickly racking up more than 100 confirmed or suspected cases.
They are the latest of numerous outbreaks, many involving hundreds – even thousands – of cases, reported in the Pacific in recent years. It appears inevitable that other island nations in the South Pacific already grappling with dengue will also be hit by Chikungunya.
AUSTRALIA IN FIRING LINE
In Australia, Ae. aegypti is well-established in Queensland’s north, where it causes annual outbreaks of dengue fever. Ae albopictus is on our northern ‘doorstep’ and, according to local experts, is virtually certain to establish a foothold on the mainland.
Worryingly, albopictus is more climate-tolerant than its tropics-loving cousin and could take up residence in southern states, too.
To date this year, 41 Australians have been infected with Chikungunya, while 1171 have contracted dengue, according to official national figures.
All of our Chikungunya cases and most of the dengue infections occurred during overseas travel to tropical destinations such as Asia – particularly Bali and Thailand – and Papua New Guinea.
COST A BARRIER TO VACCINE DEVELOPMENT
The only shadow over the future of the promising Chikungunya vaccine is cost: Despite its effectiveness, the market for the vaccine simply may not be big enough to justify the investment, senior CDC microbiologist and arbovirus specialist, Dr Ann Powers warned.
“The cost of development of a vaccine — from preclinical studies to vaccine registration — is estimated to be US$200 million,” Dr Powers said when commenting on the trials.
“Yet, even with this need for substantial funding, vaccines are still the most cost-effective strategy for disease prevention. In view of the burden of Chikungunya outbreaks, which have affected up to 63% of local populations in a matter of months, the continued development of this VLP vaccine candidate, along with other vaccine options, should be encouraged.”
Even if the investment can be justified, it will be years before the vaccine gains regulatory approval and is licensed.
FACT FILE ON CHIKUNGUNYA
This week, the US’ CDC released a new map (see main picture) and information of the regions of the world affected by Chikungunya. For travellers visiting the tropics, here’s more on the virus and tips for avoiding infection:
Funny name… Pronounced CHI-kən-GUUN-yə, the name comes from the Kimakonde language of the Makonde tribe of Tanzania and Mozambique. It means ‘that which bends up’ because those infected are often contorted with severe joint pain.
What it is: A viral disease spread by the bite of an infected female Aedes aegypti and Aedes albopictus mosquitoes. Both have distinctive bands.
Where it’s found: The disease occurs in Africa, parts of the Pacific, Southeast and South Asia, including the Indian subcontinent. In recent decades, the mosquitoes that spread Chikungunya and dengue have been detected in some parts of Europe and the Americas, including the USA, as well as Asia and the Pacific.
Danger times: Aedes mozzies bite during daylight hours – especially in the early morning and late afternoon. Both species are found in cool, dark places in and around human accommodation. A. aegypti will also readily feed indoors, while A.albopictus can also be found in semi-urban areas (such as parks) and even rural areas.
Signs and symptoms: After the bite of an infected mosquito, onset of illness usually occurs between 4-8 days but can take as long as 12 days. Infection may go unrecognised or be misdiagnosed in areas where dengue occurs.
How it’s treated: Just as there is no vaccine, there are no specific drugs to cure Chikungunya infection. Treatment relies on relieving joint pain and other symptoms, and includes rest, fluids, and medicines such as ibuprofen, naproxen, acetaminophen, or paracetamol. Aspirin should be avoided.
In rare cases: In rare cases, eye, neurological and heart complications can occur, as well as gastrointestinal illness. Serious complications are uncommon, but Chikungunya can contribute to death in older people.
Once-only infection: Chikungunya virus infection (whether clinically apparent or ‘silent’) is thought to confer life-long immunity. (In contrast, it is possible to get dengue fever more than once – in fact, subsequent infections from other dengue subtypes can result in more severe illness, including dengue haemorrhagic fever.)
(Infected persons should be protected from further mosquito exposure (staying indoors in areas with screens and/or under a mosquito net) during the first few days of the illness so they don’t contribute to the virus’ transmission cycle.)
MAKE YOURSELF A SMALL TARGET
Preventing insect bites – especially pesky mozzies – has become an increasingly important part of staying healthy during overseas holidays.
Besides Chikungunya and dengue, mosquitoes also spread diseases such as potentially fatal malaria, yellow fever, and West Nile fever, as well as filariasis. In Australia, they transmit Ross River fever, Barmah Forest, and Murray Valley encephalitis.
To avoid insect bites, including flies, sand flies, midges, and ticks travellers should:
Use insect repellent containing DEET, Picaridin, oil of lemon eucalyptus, or IR3535 on exposed skin. Read more on using repellents.
Wear long sleeves and pants, especially when mosquitoes are most active. If you expect mosquitoes or other insects to be a particular problem, treat clothes with permethrin, a safe contact insecticide.
Check screens on windows and doors to ensure they are intact and will keep mosquitoes out. If necessary, sleep under a bed net to avoid dawn raids by mosquitoes.
The CDC also has lots of advice and information on Chikungunya.