Dengue fever spreading: The view from Brazil

This is a guest post by Miriam R. Alvarado, a post-bachelor fellow and global health data specialist at the UW’s Institute for Health Metrics and Evaluation.

The global rise in dengue cases (somewhat dated, but the trend is the point....)
The global rise in dengue cases (somewhat dated, but the trend is the point….)
WHO

Dengue, aka breakbone fever, is rapidly expanding its reach across the planet.

Dengue is the fastest growing disease in Brazil. From 1990 to 2010, the median percent change in disability-adjusted life years (DALYs) was 1040%, as shown in the Institute for Health Metrics and Evaluation’s (IHME) online arrow diagram data visualization tool below.

In 1990, in Brazil, there were 78,000 cases of dengue according to the latest Global Burden of Disease (GBD) study. By 2010, this number had increased to over 980,000 cases. The BBC reported that there had already been 200,000 cases in January and February alone of this year.

The rapid rise in dengue cases in Brazil is not unique. Many countries in the region and elsewhere have experienced increases in the burden of dengue. Proven strategies exist to combat dengue and the dengue-causing mosquito, and new approaches are being developed.

But Brazil’s battle against dengue is worth special scrutiny because this country is one of the world’s up-and-coming ‘emerging markets,’ and improving health is a top priority on its development agenda. How is it doing against the spread of this expanding mosquito-borne disease?

DengueArrowSnap

Deaths from dengue are still low compared to other leading causes. There were an estimated 233 deaths from dengue in 2010, up from 20 deaths in 1990, but there were 1,139 deaths from typhoid fevers.

While 9 out 10 of the top communicable diseases in Brazil have decreased from 1990 to 2010, dengue has seen dramatic increases in the last years both in terms of mortality and morbidity across most age groups (see screen grab below of death counts by age).

While dengue was eliminated in the Americas more than fifty years ago, the dengue-causing mosquito has re-infected many countries in the region.  There are four strains of dengue. In Brazil, the re-emergence of the fourth strain after 28 years may explain some of the recent spike, as fewer people have immunity to this particular strain. In 2002 the severity of dengue cases increased, according to a presentation given by Dr. Giovanini Coelho at the Brazilian Ministry of Health during a conference in April.

Other countries in the region have also seen increases in dengue, such as Mexico and Panama. The government of Costa Rica recently issued a warning on dengue, and estimates have been reported that there are four times as many cases of dengue in Costa Rica this year than for the same months in 2012.

dengue global risk map
WHO

Rapid urbanization and increased movement of people and goods are two possible explanations for this rapid increase in dengue cases.

I asked Professor Donald Shepard of Brandeis University for his thoughts. Shepard, who has studied dengue while at Schneider Institutes for Health Policy, explained that the dengue-causing Aedes aegytpi mosquitoes “do not fly very far… so the high population densities of urban areas favor transmission.”

Aedes aegypti mosquito
Aedes aegypti mosquito

Dengue is more likely to disproportionally affect the urban poor, due to risk factors such as higher population density and a lack of reliable water and sewage systems which can create ideal breeding grounds for these mosquitoes.

What can be done? Vector control programs and community awareness and empowerment campaigns are both proven strategies to reduce the burden of dengue. Good data are also important, as the number of cases of dengue have been historically under-reported.

Professor Shepard pointed out that the Ministry of Health in Brazil “has a lot of experience in dealing with dengue fever and vector control… and has a good surveillance system… [However] curbing the rise in infections is a global challenge, as dengue is not affected by national boundaries.”

When asked whether what we’re seeing in Brazil is likely to happen in other countries, Professor Shepard responded:

“Unfortunately the answer is yes. This is currently happening not only in Brazil, but in many other countries as well … Recent estimates suggest that there may be up to 3.6 billion people at risk and more than 400 million infections annually, of which about 25% are symptomatic and result in about 20,000 deaths.”

A dengue vaccine is currently in development and is in the experimental trial phase. Professor Shepard noted that “ongoing research suggests that a safe and effective vaccine against dengue should be possible.” He adds that an effective vaccine will probably be available within a decade and possibly sooner.

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