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Published: September 12th 2017
According to the World Health Organization (WHO), "neglected tropical diseases" (or NTDs) refers to a diverse group of communicable diseases that are prevalent in tropical and subtropical conditions and affect over one billion people annually, often in the most underdeveloped regions of the world. The term "neglected" is used to differentiate these diseases from the three communicable diseases that typically receive a much greater portion of international research and treatment funding: HIV, tuberculosis, and malaria.
While there is neither a precise nor exhaustive list of all neglected tropical diseases, as of 2017 the WHO had prioritized twenty such diseases: Buruli ulcers, Chagas disease, dengue and chikungunya, dracunculiasis, echinococcosis, yaws, foodborne trematodes, African trypanosomiasis, leischmaniasis, leprosy, lympathic filariasis, onchocerciasis ("river blindness"), rabies, schistosomiasis, soil-transmitted helminthiasis, taeniasis/cysticercosis, trachoma, chromoblastomycosis, scabies, and snakebite envenoming. Due to a lack of both international funding and local surveillance data, the worldwide prevalence of many NTDs can only be estimated. However, the ones that are the most common include soil-transmitted helminths (~1.5 billion infected), schistosomiasis (~200 million infected), lymphatic filariasis (~120 million infected), dengue (~50-100 million infected), onochocerciasis (~37 million infected), and trachoma (~20 million infected).
While Laos is home to a number of neglected tropical
diseases, dengue is undoubtedly one of the most feared, in part due to its potential lethality and in part due to its increasing prevalence over the past half-century. Between 1960 and 2010, the rates of dengue worldwide increased 30-fold, with over 70 percent of those at risk living in Asia and the Pacific. The reasons for this rise are varied but include population growth, increasing urbanization (the mosquitoes that carry dengue often live in urban or semi-urban settings), international travel, and global climate change (which increases potential habitats for the mosquitoes).
Dengue is caused by the appropriately-named dengue virus, an RNA virus that belongs to the Flavivirus
genus, which also includes such members as the yellow fever virus, the West Nile virus, and the Japanese encephalitis virus. The dengue virus is spread by mosquitoes of the Aedes
genus with humans and other primates being the primary hosts. The characteristic symptoms of dengue include sudden-onset fever, headache (often behind the eyes), bone/joint pain, and occasionally a rash. The majority of cases are relatively mild and symptoms can often be managed at home with rest and oral rehydration therapy. In about 5 percent of cases, however, the disease can progress to
a life-threatening "critical" phase in which plasma leaks from blood vessels throughout the body, resulting in decreased blood flow to vital organs and, potentially, shock and death. This is called severe, or hemorrhagic, dengue. In these cases, it is imperative that patients be admitted to the hospital and receive IV fluids immediately.
Unfortunately, dengue cases in Laos are increasing at an alarming rate this year. In the first six months of 2017, over 3,000 cases of dengue were reported throughout the country, with almost a quarter coming from Vientiane Province, just north of the capital city. By contrast, in 2016, there were 249 reported cases of dengue in the entire country between January 1st and June 30th. In order to prevent a more serious dengue outbreak, the Ministry of Health's Center for Information and Education for Health (CIEH) and I worked together to produce a short video about dengue that educates people about the causes, symptoms, prevention, and treatment of the disease. The video focuses primarily on the recent outbreak in Vientiane Province and includes footage from a community mobilization event in the village of Bon Phonsu, where many of the first cases of dengue were reported this year.
The mobilization event encouraged people in the village to follow the five "steps" of dengue prevention, many of which are aimed at controlling the local mosquito population by draining stagnant water, distributing guppy fish that like to eat mosquito larvae, and cleaning up trash and weeds around the village. Interestingly, Bon Phonsu is also home to a large number of local auto mechanics. As a result, there are literally hundreds of old tires laying around the village, which tend to accumulate stagnant water in the rainy season and are notorious breeding sites for mosquitoes. Therefore, stacking these tires and punching holes in them to drain stagnant water was also stressed as an effective preventative measure in the village.
As with most NTDs, there is not currently a widely available vaccine to prevent dengue, in part due to a lack of resource allocation and funding. However, the dengue virus provides an additional barrier to vaccination development: there are actually five different strains of the dengue virus, which differ by having slightly different protein molecules required for replication. Thus, having immunity to one strain of the virus does not necessarily provide immunity to the other strains due to differing antigenicity. To
make matters even more complicated, it is believed that the severe, or hemorrhagic, form of dengue is more likely to occur upon secondary infection after a person has already been exposed to (and produced antibodies against) a different strain of the virus beforehand. Thus, providing a vaccine against one strain of the dengue virus could actually increase the risk of a patient developing severe dengue if he/she is later infected with a different strain. The solution to this problem would be to create a vaccine that provides immunity against all five strains. While there is currently a partial vaccine available in Indonesia and the Philippines (called Dengvaxia) that protects against four of the five different strains of dengue, the vaccine is quite expensive (about US$200), needs to be given in three doses, and is about 80-90 percent effective. Thus, for the time being, dengue elimination efforts around the world continue to focus on preventing transmission from the mosquito in the first place by destroying mosquito breeding sites and wearing protective clothing in endemic areas.
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