dengue

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Why global health? Polio in Syria, Texas dengue, West Nile’s killer cousin | 

Dengue is spreading globally
Dengue is spreading globally
CDC

Taken in isolation, the news reports that polio appears to have returned to Syria for the first time since the late 1990s, that dengue and yellow fever is showing up across the southern United States and that Texas has had its worst year ever for West Nile virus all seem like separate disease outbreaks.

And they are. But taken together, they should also serve as a reminder that disease, especially infectious disease, doesn’t spread independent of human behavior – and bad behavior on the other side of the planet can kill here.

Child receives polio vaccine
Child receives polio vaccine
UNICEF

If polio is confirmed in Syria, most would agree it’s legit to blame this on the disruption in public health services due to the civil war.

The rise of dengue and yellow fever in Los Angeles or Dallas is sometimes attributed to warming temperatures due to climate change, which it may be, but the spread of these ‘tropical diseases’ out of the tropics is also just as likely the result of growing global urbanization (the mosquitoes that carry these bugs seem to like cities), long-distance travel and ineffective disease control measures. Continue reading

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

Continue reading

Should my bacteria worry about genetically modified mosquitoes? | 

Flickr, Gustavo

I hate to admit it, but I kind of like the idea of genetically altering mosquitoes — or the bacteria they carry around — to fight disease.

I’m enough of a geek to think this is cool stuff and, frankly, I am not that fond of mosquitoes. But then I start to worry about how this could impact my own bacteria … Tom Paulson the microbiome.

I’ll explain that shortly, but first it needs to be said that this once-novel idea of producing GM skeeters is no longer so novel.

Turns out, lots of labs are now working on some variation of genetic modification in mosquitoes aimed at undermining the bug’s ability to spread disease whether it be malaria, dengue or some other ‘vector-borne’ illness. I seem to read a story about genetically modified mosquitoes every other week. The Gates Foundation funds a number of these projects.

So the media may still think this approach is new, wacky and weird. But it isn’t really. I can’t seem to find a comprehensive list of all the US-based projects for genetically modifying insects, but here’s an old but good overview by the Pew Charitable Trust and a more recent European Union report listing thousands of such projects or proposed projects.

Perhaps the best story of late on GM skeeters is by Michael Specter, in the New Yorker — about Oxitec‘s GM mosquito factory in Brazil. (Non-subscribers have to pay to read it, but it’s well worth the price).

Another such project was reported recently by scientists at Johns Hopkins University (my alma mater), in which a common bacterium found in the guts of these bugs was altered to secrete proteins toxic to the malaria parasite. They report that these toxins harm neither humans or mosquitoes.

I haven’t read their paper so I can’t tell how they tested the human toxicity. Chances are, it was a fairly quick test that looked at immediate harm to human cells or something like that. The problem here is that, when it comes to testing human harm, these quick toxicity tests may be almost meaningless. Continue reading

Lacking a dengue vaccine, scientists tinker with skeeter genes | 

It’s rarely on most Americans’ minds, but worldwide dengue is a big killer. And it’s spreading fast.

The U.S. Centers for Disease Control and Prevention says there are anywhere from 50 to 100 million people infected every year with dengue — including a very small, but increasing number of Americans — and an estimated 50,000 deaths from this mosquito-born disease.

Here’s an interactive look (go to this link) at dengue around the world from HealthMap:

HealthMap, CDC

The number of cases of dengue have exploded over the past few decades in tropical and semi-tropical regions. Some believe this may be driven by climate change and an expanded range for the mosquito (Aedes aegypti, which also carries yellow fever).

WHO

Dengue cases over time

Others think shipping, cargo transportation, may be the main route of spread. This skeeter tends to like to live in urban and semi-urban areas.

Because of the global surge in dengue, the U.S. military and some pharmaceutical companies have stepped up efforts to develop a vaccine that can protect against the infection. The Bill & Melinda Gates Foundation has donated $60 million to the vaccine efforts as well as some more ‘innovative’ approaches such as modiying the genes of mosquitoes.

Earlier this week, a team of scientists (partly funded by Gates) reported success in a field trial of mosquitoes genetically modified so that their offspring die following reproduction. As the BBC noted, dengue can’t be fought with same tools as malaria, such as bed nets, primarily because these mosquitoes bite during the day time.

The successful field trial — which just tested the genetic tinkering’s effect on reproduction, not dengue transmission — has nevertheless raised concerns about unintended environmental side-effects, the New York Times reports. 

The British biotech company pursuing this approach, Oxitec, had already raised some hackles earlier for too aggressively moving forward with their releasing modified mosquitoes into the wild.

Meanwhile, to much less media attention and fanfare, other scientists (many of them also funded by the Gates Foundation) are working on developing a vaccine against dengue. Here is one recent news brief about an ongoing trial.

For a broader overview of work on developing a vaccine, see the Dengue Vaccine Initiative.

Altered skeeter update: Infecting mosquitoes to fight dengue | 

Flickr, Gustavo

The idea of altering mosquitoes to fight disease appears to be quite contagious.

It’s almost become a news category unto itself, with at least a story every month or so involving something like:

Bacteria.

Scientists in Australia want to expand upon successful field tests indicating that infecting mosquitoes with a particular bacteria, known as Wolbachia, prevents the bugs from transmitting the dengue virus.

WHO

Dengue cases over time

Dengue, also known as dengue fever or “break-bone” fever, is exploding worldwide and so there are a number of efforts underway to stave off the epidemic, including finding a vaccine and, well, messing with mosquitoes.

Here are a number of good stories on the latest strategy aimed at fighting disease by messing with mosquitoes:

NPR:  Better you than me: Scientists sicken mosquitoes to stop dengue

WashPost: Field tests show bacterial oddball may be a dengue destroyer

Nature News: Bacterium offers way to control dengue fever

Guardian: Injecting mosquitoes with bacteria could stop dengue fever

Few of the news reports go into much detail scrutinizing the potential adverse side-effects, whether to humans, the environment or the skeeters, but that’s routine for news stories based on early stage scientific studies.

The bacterium, Wolbachia, is a common insect infector and is widely regarded as fairly benign if not downright beneficial. Still, you never know when you fool with Mother Nature — which is why we do phased scientific testing.

Another problem with any intervention is evolution, aka resistance. Bugs have a way of finding ways around things that get in their way. Still, the scientists say, if this approach can work for a decade or so we will do much to hold the dengue explosion at bay.

I’ll be writing more later about the dengue vaccine research, which is perhaps less exciting than manipulating skeeters but perhaps more feasible.

 

Dengue Fever in Florida, On the Rise Globally | 

Aedes aegypti mosquito

CDC

Dengue is spreading globally

Dengue fever, also known as “breakbone fever,” used to be confined to a small part of the tropics. As a recent outbreak in Florida illustrates, it is no longer so confined.

In fact, dengue is now the most common and the fastest-growing mosquito-borne disease in the world, currently threatening a third of the world’s population.

In the worst cases, the infection can cause a potentially deadly form of the disease known as dengue hemorrhagic fever (DHF). Epidemics of both dengue and DHF are now routine in many parts of Latin America only several generations after the mosquito-borne virus was first identified there.

Dengue cases over time

WHO

Dengue cases over time

Due to the combination of human travel, cargo transportation and perhaps the changing climate, the mosquito that carries the dengue virus (Aedes aegypti, which also carries yellow fever) has been spreading to nearly all tropical and semi-tropical regions worldwide. This skeeter tends to like to live in urban and semi-urban areas.

Because of the global surge in dengue, the U.S. military and some pharmaceutical companies have stepped up efforts to develop a vaccine that can protect against the infection. The Bill & Melinda Gates Foundation has donated $60 million to these efforts as well.