Break Bone Fever

Pathogens & People: Mosquitoes and 'break bone fever' By EDWARD McSWEEGAN, For The Capital Published November 02, 2008

I went to India last week. Aside from the usual packing and planning for a long trip, I also had to run over to the clinic for tetanus and typhoid booster shots, azithromycin for bacterial infections, loperamide for gastrointestinal problems and atovaquone/proguanil for malaria. India is not Bermuda. I've never had any health problems there, but the anti-malarial meds sometimes worry me. Not because of any side effects or because they are ineffective, but because having taken them there is a tendency to think you are protected from mosquitoes. You're not; you're only protected from malaria, and mosquitoes - as with modern fighter planes - carry a variety of other armaments with which to do harm. I have written about other mosquito-borne infections such as yellow fever, West Nile fever and chikungunya. But last week's trip brought to mind yet another such infection called dengue. Just before the trip, the newspapers in New Delhi were reporting a large outbreak of dengue fever in the capital. There were 800 cases, and probably many more that were not detected and reported to health officials. Dengue is caused by a virus similar to the mosquito-borne viruses that cause West Nile and yellow fever. The virus causes fever, severe muscle aches, bone and joint pain, headache and eye pain, chills, and frequently, a skin rash. Dengue hurts; it isn't called ''break bone fever'' for nothing. Worse yet, the infection may progress to a severe condition called dengue hemorrhagic fever with internal

bleeding, shock and possible death. The acute, painful symptoms of dengue may disappear after a week, but fatigue may persist for several weeks. There is no specific treatment. Medical care consists of intravenous fluids and common drugs for pain and inflammation. Unfortunately, recovering from a bout of dengue is not a guarantee you won't get it again. Indeed, it is possible to get it four times because there are four separate virus serotypes (DEN 1-4). Immunity to one type does not confer immunity to another type. This is why a vaccine has not yet been developed. An effective vaccine has to provide protection against all four virus types. Writing in Nature Medicine in 2003, two Massachusetts researchers noted, "the immune response to viruses treads a fine line between damage to the host and control of the pathogen." That is especially true of the four dengue virus types, which complicate both normal immune responses and the development of effective vaccines. For example, a previous bout of dengue can actually make a second bout even worse than the first. The initial immune response actually enhances the second infection and sometimes leads to the more severe DHF or shock. One of the great challenges to testing a dengue vaccine is to ensure the vaccine protects against the four viruses without over-stimulating the immune system and causing DHF. Dengue, unfortunately, is not an infectious disease confined to "the far side of the world." It is endemic in a 100 countries in Southeast Asia, the Americas, parts of the Caribbean and the Mediterranean, and the western Pacific. The World Health Organization estimates 2.5 billion people are at risk from dengue and 50 million cases occur annually. Cuba, for example, had significant dengue and DHF epidemics in 1977 and 1981. Cases of dengue occasionally threaten to sneak across the Texas border from Mexico. Ironically, a coach potato lifestyle - conducted in front of the television, inside screened and air-conditioned houses - seems to keep Texans away from mosquitoes and the dengue virus.

Still, the U.S. does have a small number of dengue cases each year. These are usually ''imported'' by tourists returning from the Caribbean and developing countries such as India. The Centers for Disease Control and Prevention found 216 suspected cases of imported dengue during 1999 and 2000. Dengue is passed from person to person by two types of mosquitoes: Aedes aegypti and Aedes albopictus. Both mosquitoes are found in the U.S., but again, lifestyle, mosquito control and high-quality medical care are likely to keep dengue from becoming established in the U.S. Unfortunately, that's only true of dengue the virus. Dengue Fever, the surfer dude rock band that blends 1960's Cambodian pop with psychedelic rock already has established itself in Los Angeles. I've never heard this unique blend of music, but at my age, I'm guessing dengue fever would be much less painful than Dengue Fever.

Dr. Edward McSweegan has a Ph.D. in microbiology and lives in Crofton. He works on and writes about infectious disease issues. He may be contacted at [email protected].