Two-Fifths of Earth's Population at Risk

Vibrio cholerae
Cholera. One of the most aggressive water-borne infections, cholera can kill within 24 hours, and has caused seven pandemics in history. It occurs in over 60 countries worldwide. Currently, the World Health Organization(WHO) has warned that cholera is a serious risk in the Democratic Republic of Congo, where there have already been 1,000 cases since October. Of course, most Americans are unfamiliar with cholera since the last outbreak in the U.S. was in 1911. And I don’t think any of us were around for that.

Cholera is a bacterial infection of the intestine that comes from consuming infected food or water. Symptoms begin with sever diarrhea and vomiting, which then lead to dehydration. Blood pressure falls, cramps develop in the legs and abdomen, and then body temperature drops as organ failure occurs. Not a pretty picture. There is hope however.

Researchers have now developed a system to predict cholera outbreaks, by using satellite monitoring of marine environments to predict cholera outbreaks. It turns out that outbreaks follow an increase in sea temperature. The satellites measured sea temperature and the amount of phytoplankton in the Bay of Bengal. When sea temperatures increased, so did phytoplankton densities. And then followed cholera. But why? Perhaps food availability. The cholera pathogen lives in the gut of a zooplankton species known as copepods. And as sea levels rise, copepods find their way into the water supply, and that is how people become infected.

This method could provide an early warning system for places like India and Bangladesh, where cholera epidemics occur regularly. Professor Rita Colwell of the University of Maryland says that satellite monitoring is the key to preventing cholera epidemics. “We can use the current data taken from the satellites to predict when the onset of cholera epidemics will occur, it allows public health authorities to pinpoint exactly when to allocate resources or implement warnings about drinking the water,” she said. Another method to fight cholera is very simple- use cloth filters to filter plankton out of drinking water, which can reduce cholera by 40 to 50 percent.

Dengue fever is another illness that most Americans are unfamiliar with, unless they have encountered it in their travels. According to WHO, 2.5 billion people, or roughly two-fifths of the earth’s population, is at risk from dengue. Although it has a low death rate (~2.5 percent of hospitalized patients), it is an incredibly painfully illness in which one experiences intense joint and muscle pain and crushing headaches. Thus it has earned the nicknames of “breakbone fever” or “bonecrusher fever”. It is the second most common cause of feverish symptoms in Western tourists returning from developing countries, the first being malaria.

In the most serious cases, symptoms include severe headaches, rapid onset of high fever, debilitating joint and muscle pain, nausea, vomiting and internal bleeding. The disease is costly because patients require constant monitoring and care. Each year, there are 500,000 hospitalizations due to dengue.

The worst cases, or dengue hemorrhagic fever (DHF), are believed to occur when a person that has already been exposes to one of the four strains of dengue is then exposed to another strain. This is not usually travelers, but children.

There is hope for the 50 million infected each year. Military scientists are working on a dengue vaccine at the Armed Forces Research Institute of Medical Sciences. “We’re further along with the dengue vaccine than we’ve ever been,” said Duane Gubler, the director of the emerging infectious diseases department at the Duke-N.U.S. Graduate Medical School in Singapore. “There’s a good possibility that we’ll have a vaccine in five to seven years.”

Which is good, considering a new study in the November issue of the American Journal of Tropical Medicine and Hygiene. The study is conducted in part by Dr. Barry Alto, who has the longest title ever as Director of the Medical Entymology Program at the Illinois Natural History Survey, a division o the University of Illinois’ Institute for Natural Resource Sustainability. The researchers tested both the Asian tiger mosquito and the yellow fever mosquito, the 2 main transmitters of dengue. They measured the mosquito’s wings and then fed them blood packed with dengue virus. It turns out the smaller mosquitoes were more likely to become infected, and are thus more likely to transmit disease. Guess we should all watch out for those no-see-ums!

Other pandemics of interest


Transmitted by various female sandflies, there are three forms of leishmaniasis. Cutaneous leishmaniasis consists of a large number of skin ulcers (around 200 or so). Mucocutaneous leishmaniasis produces extensive damange and disfiguration to the cartilage and mucous membranes of the nose and mouth. Visceral leishmaniasis, the most severe form, consists of fever, extreme weight loss, anemia, and swelling of the spleen and liver. If left untreated, it has a mortality rate of almost 100 percent.


Caused by the bacteria known as a spirochete (the same bacteria that causes syphilis), it is contracted by drinking water contaminated with animal urine. It is found worldwide, but is more common in warmer climates. Initially it resembles malaria, but more serious complications include kidney failure, meningitis and jaundice.

Not pandemics, but still interesting


Another beauty transmitted by mosquitos, lymphatic filariasis causes fever and inflammation of the lymph nodes. Chronic swelling of usually the leg or foot occurs, frequently resembling an elephant’s foot….hence the name “elephantiasis”.


A skin infection caused by the larvae of certain flies in the tropics. The eggs of the fly are attached to the underside of a mosquito, where they then penetrate the skin while the mosquito feeds. Boil-like lesions develop at the site of penetration, and transient, shooting paints occur at the site. Gross factor: There is a tiny opening at the top where the maggots get their air. EW!

Okay, so this last one is not a disease, but it is interesting. Enter, the candiru fish. This little (1 inch) parasitic sucker is a bit of a vampire. It lives in the Amazon and Orinoco rivers, where if you are unfortunate enough to attract it with your urine, it will swim into your urethra (or other “special places”) , where it will lodge itself with its spine and gorge itself on your blood. Once engorged and stuck, there is no way out except for surgical removal. OUCH!

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