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Posted by Dr. Sushrut Jangi February 11, 2013 07:00 AM
Isles of White in a Sea of Red
Sometimes, physicians describe a finding as pathognomonic, which means that the finding almost certainly suggest a diagnosis. A good example are the white spots seen on the inside of the cheeks, called Koplik spots, which are quite specific for measles. However, pathognomonic signs are rare. Usually, a diagnosis is riddled with uncertainty. "I took one look at his legs and saw a brilliant erythema," Dr. Golding says. Erythema - a deep, red color of the skin - stood out among Mr. G's signs and symptoms. Woven through the dark red was a faint tracery of a lighter color that Mr. G had referred to as a "fishnet" in appearance. One of Dr. Golding's colleagues, who was from the Phillipines, remembered hearing about a tropical rash that presented as "isles of white in a sea of red," a pattern suggestive of dengue hemorrhagic fever.
Dr. Golding thought this was possible, especially since Mr. G had fevers and a headache, typical of the disease. Although the rash was not pathognomonic, he used it as an anchor to a possible diagnosis. He sent Mr. G's blood to a lab to get him checked for dengue. A few days later, the test returned positive.
Dengue hemorrhagic fever has a scary name. But hemorrhage - or bleeding - is rare. Most often, people develop high fevers, terrific headaches, and bone and muscle pain. Because of these symptoms, some people call dengue "breakbone fever." Eventually, the virus is tackled by the immune system and the host gets better. In a small number of cases, people fall very ill and can even die. The disease is caused by a flavivirus - a family of pathogens that cause similar illnesses including yellow fever, West nile, and Japanese encephalitis. Most of these viruses are spread by mosquitoes. In the language of epidemiology, since mosquitoes carry the disease from human to human, they are vectors; we are the hosts. But dengue is not spread by the kind of fat, muck-water mosquitoes we are used to in Boston.
Instead, says Dr. Sharone Green, an expert in flaviviruses who works at Umass Memorial Medical Center, "dengue is spread primarily by Aedes aegypti which are different from the Culex mosquito we have here." The dengue mosquito is tiny, and is often found singly, rather than hovering in clusters like the Culex of New England. "Most people don't know if they've gotten bit." The dengue mosquitoes also feed all day long. "Many people tend to put on mosquito repellant and put up nets at night," says Dr. Green. But that's not enough to protect against the dengue mosquito who feeds at any hour. Perhaps most disturbingly, Aedes loves to live indoors. The moment it bites a person who has dengue, the mosquito remains infected for life. Consequently, a single insect may infect an entire household. "Dengue transmission is very focal," she says. "When cases occur in Puerto Rico, they are often found in little clusters of homes and neighborhoods."
So Dr. Green isn't surprised to hear that Mr. G lived in the same house as someone who might have had similar symptoms. A few days after Mr. G had received his diagnosis, he received an email from D - the woman whose husband had fallen ill in Puerto Rico. In her email, she described the disease that had afflicted M.
Hi, Yes,he (M) had it has as you left. After you left the numbers of people with the dengue skyrocketed. The goverment has increased awareness and people are really taking care of themselves. Here some neighbors in [name of the community omitted] have even a group in facebook to inform about it. We have had always had a (dengue) season but not this long. After you told me I have been telling my guests about it and that they protect themselves with Off spray, mostly in the afternoons and night that they come out. Climate change has made what has always been our dry seasons rainy seasons.
I hope it changes soon.
During his trip to Puerto Rico, Mr. G had walked into a mini-epidemic that had risen around him. Clusters of people in San Juan soon became infected. According to the CDC, reports of dengue in Puerto Rico in December of 2012 were above traditional epidemic levels. What happened throughout the region, had occurred on a smaller scale within the house where Mr. and Mrs. G had stayed. "It's possible the same infected mosquito had bitten [the host] and the patient," Dr. Green postulates. [see CDC graph]
Printed with permission from the CDC
Every Place Has Something
Although every country hosts numerous diseases, tropical countries often have more opportunities for travelers to get sick than other environments. Dr. Green recommends that anyone traveling to a warm or tropical climate should go to the travel clinic or visit their physician to get advice about the kinds of illnesses that exist in the country.
The classic reference doctors use to track illnesses globally is a book published by the Center for Disease Control called the CDC Yellow Book http://wwwnc.cdc.gov/travel/page/yellowbook-2012-home.htmhttp://healthmap.org/en/. Other references include the Health Map, founded by Boston Children's Hospital in 2006, that follows epidemics across the world in real-time by surveying official disease reports, accounts from social media, newspapers, and magazines. The project is even currently reporting on the active outbreak of dengue that Mr. G experienced during his recent trip. The same research group has even discovered that what people search on Google may help predict where nascent epidemics are emerging. Even D's email mentions a facebook group that helps monitor symptoms in the neighborhood. Epidemiology detectives now use footprints on the web and in social media to help track new epidemics of disease the moment they arise.
Using novel ways to diagnose and track illness can help travelers and natives prevent transmission early. Since dengue mosquitoes are day-biting, Dr. Green recommends frequent use of repellent and even treating clothing with permethrin. Choosing light or beige colored clothing is preferred over bright colors, which tend to attract mosquitoes. And, she says, "if [you] are sleeping in the house with someone with suspected dengue, [you] should be sure to use spray and consider using a bednet at night."
Many physicians, unlike Dr. Golding, may not recognize dengue when they see it. Patients should be aware of the diseases prevalent in a country so that if they fall ill when they return, they can bring it to the attention of the doctor. Mr. G has since recovered. The rash has faded and his fevers are gone. I don't want people to be paranoid when they travel, he says. But, as Dr. Sharone Green reminds us - "every place has something going on."
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About the authorSushrut Jangi is an internist at Beth Israel Deaconess Medical Center and an editorial fellow at The New England Journal of Medicine. More »
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