Saturday, November 21, 2015

Dengue: You don't know how big a threat it is. It's big.

Not too worried about dengue fever? 

You should be. It is the leading cause of illness and death in the tropics and subtropics. It's a miserable disease to have. 

The U.S. Centers for Disease Control and Prevention (CDC) say 400 million people annually are infected.

And there’s a lot you likely didn’t know about this mosquito-borne disease, which has showed up and been defeated several times in the Hawaiian Isands, but now appears widespread now on the Big Island. 

One feature of the disease is that there are four different related viruses that cause dengue. If you get one, you’re protected from getting that one again, but after a few months you can get any of the other three. Most parts of the world have all four types.

There is some evidence that if you get a second type after a first infection, the symptoms can be significantly more severe.

Dengue is pretty much everywhere within a thousand miles or so of the equator—Hawai`i has been one of the outliers in not having it.

There is no vaccine for it so far, although there's a lot of work being done toward a vaccine. Your best hope of not getting it is not getting bitten. 

It is possible to have the infection and not have symptoms—but you’ll still be able to pass the disease to others via mosquito bites.

Dengue is in a group of viruses called Flaviviruses. Yellow fever and West Nile are also in that group. It causes illness that outwardy mimics a lot of other disease, even flu. It can be very similar in outward appearance to another tropical disease called chikungunya. Says the CDC: “Chikungunya and dengue are both acute febrile illnesses characterized by fever, myalgia, and lethargy. Some patients may also have … rash, nausea, vomiting, and headache.” 

Fortunately, we don’t have chikungunya in the Islands. On the other hand, dengue is worse: “Chikungunya is rarely fatal. In contrast, early identification and proper clinical management for hospitalized dengue cases can reduce the case-fatality rate from 10% to less than 0.1%. Therefore, patients suspected of having dengue or chikungunya should be managed as having dengue until dengue can be ruled out.”

Dengue can be transmitted blood to blood, but the main reservoir for infection is mosquitoes. Two mosquito varieties can carry dengue, Aedes aegypti and Aedes albopictus. We have both of them in Hawai`i. Albopictus, the Asian tiger mosquito, is a daytime biter. Aegypti is a daytime biter that’s most active a couple of hours after dawn and before sunset. Aegypti is the one you’re more likely to find inside your house.

The virus is creepily robust. Most get it from the mosquitoes, but folks working in laboratories have been infected: “The virus is stable in dried blood for up to 9 weeks at room temperature,” says the Public Health Agency of Canada. Dengue isn’t in Canada, but visitors to the tropics can bring it home.

You get sick 4 days to a week after being bitten, and you can stay sick 3 to 10 days. In some people, it can progress to more serious diseases called dengue hemorrhagic fever and dengue shock syndrome, which can be fatal. These diseases are more common in young children than adults.

Folks who have traveled in the tropics often have experienced airline crews spraying insecticide up and down the aisles. Often, that’s for dengue, which can be so painful it’s called “breakbone fever.”

You avoid getting dengue by avoiding getting stung by infected mosquitoes. Recommendations are to stay out of areas with lots of mosquitoes, and to wear protective clothing and insect repellent if you must be there. Also, reduce mosquito numbers in your environment by emptying standing water where they breed in pots, plants, and other locations. 

Longer term, to stop the cycle of infection, public health authorities need to break the cycle of humans passing the disease to mosquitoes and mosquitoes passing it to humans.  If new infections can be stopped for several weeks, the cohort of infected mosquitoes can die off, and the reservoir of infectivity is shut down. A mosquito, once it picks up the virus, can pass it on for its lifetime, but does not pass it on to its young.

Once again, the key symptoms of dengue, according to CDC, are a lot of pain—headache, pain behind the eyes, joint pain, muscle pain, bone pain—and also rash, mild bleeding from the nose or gums, and bruising or red and purple spots on the skin. Lab tests will show low white blood cell counts.

Victims should seek immediate medical attention, CDC says, if the symptoms move to severe abdominal pain or persistent vomiting; red spots or patches on the skin; bleeding from nose or gums; vomiting blood; black, tarry stools; drowsiness or irritability; pale, cold, or clammy skin; or difficulty breathing.

The Hawaii State Department of Health fact sheet on dengue. 
The Centers for Disease Control and Prevention web pages
World Health Organization treatment guidelines

© Jan TenBruggencate 2015

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