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'The Smallest Enemy'

Navy NewsStand

Story Number: NNS070215-21
Release Date: 2/15/2007 4:34:00 PM

By Mass Communication Specialists 1st Class Jeff McDowell, Navy Medicine Support Command Public Affairs

SILVER SPRING, Md. (NNS) -- Despite the enormous evolution of warfare in the last century, one of the most harmful enemies of American fighting forces deployed around the world is not bullets or roadside explosives.

This enemy overtook battalions of personnel fighting in the South Pacific in World War II, in the rice paddies in Vietnam and continues to impact mission readiness to this day. What’s worse, it brutally attacks and kills innocent civilians with no regard for the rules of engagement.

More human beings have been killed by infection with the intracellular plasmodium parasites transmitted by anopheles mosquitoes than any weapon ever used in conflict. The enemy is malaria, and it is estimated that there are up to 2.7 million civilian victims killed worldwide annually.

Researchers at Navy Medical Research Center (NMRC) are waging a war of their own in an effort to develop a vaccine to combat this deadly disease.

“Malaria is the worst actor in mission-aborting potential,” explains Capt. Thomas Richie, a medical doctor and the malaria program director at NMRC.

"We had another example of this in Liberia in 2003 where we had a 44 percent attack rate in a Marine expeditionary force. It was a peacetime mission, a non-hostile theater, and the mission was aborted just 10 days after it started due to malaria infection. There were 35 evacuations with five Marines in intensive care, nearly dying because of this preventable disease.”

There have been no malaria deaths in the U.S. military since a special forces soldier died following a mission to Nigeria in 2002. However, deployed military personnel are still at risk of severe illness and even death.

Those risks prompted the research work conducted at NMRC. This research concentrates on the P. falciparum parasite, the type of malaria that leads to the greatest risk of severe illness and death.

While there are “prophylactic” medicines issued to troops who deploy to tropical regions where the malaria risk is highest. These medications help prevent the contraction of malaria. However, they are not benign medications, and side-effects can and do interfere with operations. Prophylactic malaria medicines require personnel to start taking the medicine a few days or a week before deployment. Personnel continue to take the medicine during and after deployment for one to four weeks, depending on which medicine they are taking.

It's important to keep taking the medicine post-deployment, Richie said, because the malaria parasites could remain in the bloodstream. Stopping the medicine too soon could give the parasites an opportunity to grow and cause the illness.

“As with most infectious diseases the best way to prevent it is with a vaccine. By far the most cost-effective intervention, [vaccination] switches the entire medical effort to the pre-deployment status when it can be done in a medical treatment facility,” Richie explains. “What you want is a ‘fire and forget’ approach, rather than taking prophylactic drugs.”

Malaria is a chronic infectious disease, Richie explains. It is unlike other acute infectious diseases like measles, smallpox and diphtheria. Childhood inoculations protect Americans from these diseases. If you get these diseases, you only get them once, and exposure often results in lifetime immunity to the disease. It is fairly easy to mimic this process with a vaccine.

“Chronic infectious diseases like malaria, HIV/AIDS and herpes have all evolved a capability to avoid the human immune response. These infections are chronic, evade the human immune response and persist in our bodies despite the immune response,” Richie says. “This is the conundrum; we are trying to make a vaccine by harnessing the human immune response, to kick out a pathogen that knows how to evade the immune response.”

Researchers and scientists at NMRC and many other medical research labs are confident they can develop a malaria vaccine. There are two research models that continue to show promise and prove the feasibility of making a successful vaccine.

The first model involves people who live in one of these malaria-endemic areas like sub-Saharan Africa who gradually develop a level of resistance, not to the infection, but to the clinical manifestation of the infection. This is why you can survive as a teenager or an adult in Africa. Although people are infected with malaria, after many years of exposure, they no longer get sick from malaria. This acquired resistance is the reason why many malaria victims are small children. Their systems do not develop the level of resistance and for whatever reason can’t mount enough immunity quickly enough.

The second model involves irradiated sporozoites. Sporozoites are one stage of the parasite’s life cycle. When the parasite-infected mosquito bites a human, the parasites are in sporozoite form. They travel to the liver, where they develop through a number of stages before emerging into the bloodstream and infecting red blood cells. The symptoms of malaria -- fever, chills, anemia and cerebral malaria -- are all associated with infected red blood cells. Researchers have learned that if enough irradiated sporozoites are introduced to the liver through a series of “immunizations” involving 1,000 to 1,500 controlled mosquito bites to a subject, you will develop a sterile protection against the bites of a non-irradiated, malaria-infected mosquito.

“There’s something about having these thousands of damaged sporozoites in your liver that induces an immune response that is powerful enough to kill intact parasites,” Richie explains. “That gives us hope that we can make a really powerful vaccine and prevent infection altogether.”

The fight to develop a malaria vaccine has been going on for more than half a century. Navy researchers at NMRC and scientists in laboratories around the world are working in earnest in hopes of saving not only American military personnel deployed to tropical regions but also millions of people who will continue to be struck down by the smallest enemy.