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SALUD: Dengue Reappears Worldwide with a Vengeance – WHO

Gustavo Capdevila

GENEVA, Jul 29 2002 (IPS) - Dengue fever is seeing an upsurge and continues to spread around the world, particularly in Latin America and Asia, while the African population seems to be protected from the disease by genetic factors, according to international health officials.

The World Health Organisation (WHO) says that 2002 “is a particularly bad year for dengue fever,” a viral illness that can be found throughout the world’s tropical and subtropical regions.

This year is very similar to 1998, “which saw a pandemic that affected much of the tropics more or less at the same time,” said Mike Nathan, an expert from the WHO’s department of transmissible diseases.

An unprecedented number of cases — approximately 1.2 million — were reported to the WHO that year.

However, health specialists estimate that the true figures are much higher, “probably more than 15 million infections per year,” said Nathan.

During the 1998 pandemic, there was rapid and massive transmission of the dengue virus — which occurs through bites from the Aedes aegypti mosquito. Once infected by one form of the virus, a person becomes immune to that strain, or serotype, explained the WHO expert. There is still no vaccination or cure for the disease.

The history of dengue indicates that after a major outbreak there is a year of relative calm, as occurred in 1999. Later, the disease builds up again until it unleashes a new epidemic.

“And that seems to be where we are now, in 2002,” Nathan stated.

Among the factors contributing to the development of the epidemic are climate fluctuations. Nathan mentioned recent announcements about the return of El Niño — a cyclical phenomenon causing extreme weather — though this year’s is predicted to be less intense than its last appearance, in 1997-1998.

Dengue’s symptoms include high fever, headache, muscular and joint pain, nausea and vomiting.

The worst form of the disease is haemorrhagic dengue, which can be lethal. It is characterised by extremely high fever and internal bleeding.

An individual who has been exposed to one of the four dengue virus types is immune to that strain for the rest of his or her life. But if the person is exposed to another of the three serotypes, there is an increased risk of severe disease, including haemorrhagic dengue, explained Nathan.

The current WHO information on dengue is focused on Latin America because the region’s reporting is more complete than other parts of the world.

In the Americas, this disease — which had nearly been eradicated in the battle against yellow fever, which is transmitted by the same mosquito species — saw a strong re- emergence in the 1960s, taking root in tropical regions, then extending to the subtropics.

This year, Brazil suffered a very severe dengue epidemic during the first quarter, with the highest number of cases reported in the region: 555,691. Nearly half of the infections occurred in Rio de Janeiro.

Of the total cases in Brazil, around 2,000 involved haemorrhagic dengue. The WHO received reports that there were 84 deaths caused by the disease in that period, said the United Nations agency’s expert.

Dengue appeared against this year in El Salvador, where 3,500 cases were reported, 90 of which were haemorrhagic dengue. Honduras has seen a total of 3,000 cases, and Nicaragua some 500.

In Mexico’s southern states, at least 2,300 people have been infected, while the disease “is certainly occurring in many other countries, like Venezuela and Colombia, where there are large numbers of cases,” Nathan said.

The specialist explained that information form Southeast Asia is reported to the WHO with several months delay ” before we get the real picture.”

However, he said, the current “hot spots” for dengue are in Malaysia and the southern provinces of Laos.

“There is a seasonal upsurge, perhaps a little more than the average year in Cambodia, as well as unusual activity in southern Thailand, while Vietnam is also showing increasing number of cases,” he said.

The panorama for the region will be completed once all reports on the dengue phenomenon are in, including those from Philippines, China and Taiwan.

With respect to Africa, Nathan pointed out that “there is no routine report of dengue,” though the presence of the virus on that continent has been confirmed.

But there has never been any report of dengue epidemics in Africa, “which is the striking difference between that region and the other epidemic regions.”

One part of the explanation for the absence of dengue epidemics in Africa emerged from the disease’s history in Cuba, a Caribbean island that was free of dengue for a long time.

Cuba recorded epidemics in 1978 and 1981, and in both cases the phenomenon was extremely well documented by the health specialists on the socialist-run island, said Nathan.

Through analysis of the ethnic backgrounds of the Cuban population, it became clear that there was some predisposing genetic factor among Afro-Cubans that protects them from serious manifestations of dengue infections.

Cubans of African descent contract the disease, but the severest forms of haemorrhagic dengue are extremely uncommon, according to the WHO.

“This has also been seen in Haiti. So it is a genetic factor that seems to be protecting people of African origin” from the dengue virus, said Nathan.

 
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