Daily Science Dose

You may have heard of a strain of encephalitis: the West Nile Virus, with West Nile encephalitis being the most severe form. West Nile is actually a form of Japanese Encephalitis, a mosquito-borne disease that causes inflammation of the brain. There are other strains of encephalitis including Saint Louis (named for the American city where it was first diagnosed in 1933), La Crosse, Western and Eastern Equine, and tick-borne encephalitis.

The danger with encephalitis is that with other “vector-borne” or mosquito-borne diseases is that mosquito populations are generally held in check by cold winters around the world. Most mosquito-spread illnesses are mitigated by climate, but as we see the world warming up, tropical zones spreading into previously temperate areas, and winters becoming milder and wetter, mosquitoes that carry diseases are finding favorable conditions in more and more places.

Mosquito babies love stagnant water.

As far as the individual strains of vector-borne encephalitis go, they are all quite similar, as the virus is spread from an infected bird or mammal, and the animal’s blood carried by a mosquito will enter the bloodstream of the mosquito’s next victim, possibly a human. The virus, a flavivirus much like Malaria, will then enter the human’s bloodstream, and start to cause all sorts of damage if the disease becomes severe enough. Many times, the human host will not experience severe symptoms, maybe a headache with a fever. Severe symptoms can include neck stiffness, stupor, disorientation, coma and convulsions. Some cases result in death, up to 60% for Japanese encephalitis, but usually death occurs in older people and children. St. Louis encephalitis has a possible death rate of 5 to 30%.

Treatment for encephalitis is important, despite there being no specific medication to treat the disease. Severe cases are hospitalized, and support treatment is given. There is no vaccine currently approved by such health organizations as the Centers for Disease Control.

Another problem with some strains of encephalitis, like the La Crosse Strain, is that people are moving into areas that were previously left unpopulated, such as rural and wilderness areas in the Great Lakes region of the United States and into the hardwood forests of Midwest. Luckily, the La Crosse strain is still considered rare, but in areas of the world where growing populations are requiring more and more space, like Asia, encephalitis is more common.

The range of Japanese Encephalitis

Historical data of occurences of St Louis Encephalitis in the US from 1964.

West Nile cases in the US during 2008.

With a warming world, mosquitoes can be expected to not only survive winters, but find more favorable habitats. With global warming, precipitation increases. With more rain, both in quantity and incidence of storms, water will pool up and most likely not have the time to dry up. This water is like an invitation to mosquitoes. In the grand scheme of things, usually the same watering holes that host mosquito families will host frogs and other creatures that eat the mosquitoes. But mosquitoes can find a home in much smaller pools of standing water, and frogs need water that is more established as their life cycles take longer to move from tadpole to frog. More rain means more mosquitoes without the necessary increase in frogs. And don’t forget…the research lately has been showing that frogs are experiencing their own set of problems and a decrease in their numbers around the globe.

As with most arboviruses (arthopod-borne), it is important to avoid mosquito bites. Wear insect repellant, build bat boxes around your yard, wear long sleeves and pants when outside, avoid having standing water around your house and yard (even birdbaths and little ponds). Check out the CDC website for more information.

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We have been looking at the danger posed by once-tropical diseases spreading into more temperate zones as the world warms. Hey, that may be a good idea for a new soap opera, As the World Warms. Just remember, you heard it her first.

First we looked at Malaria and Dengue Fever, and today’s topic is our not-so-friendly stomach flora, Cholera.

The yellow areas are local cholera outbreaks, and the black dots represent imported reported cases. I believe Alaska is only colored yellow due to it being part of the US.

Cholera is a water-borne and food-borne (as water is a major component in food production) disease that is spread by the Vibrio cholerae bacterium. According to the Centers for Disease Control (CDC), cholera has not been present in the industrialized nations in 100 years, other than the rare case of a traveler returning to a non-cholera country from a nation where cholera is common, for instance India and Sub-Saharan Africa. In fact, cholera is currently at “pandemic” status in the poorer parts of the world

The major problem with getting cholera is that the bacterium causes an intestinal infection which leads to diarrhea. The problem with diarrhea is of course dehydration. If your body er, uh, ejects too much fluid before that fluid can be replenished, you can die. Remember in high school US history classes, when you were studying any of the major wars, and it would come up that not every casualty was due to violence, but that some soldiers died from things like dysentery. Dysentery is a severe intestinal infection that also causes rather horrible diarrhea…a terrible way to die.

Cholera is easily treated, but that treatment is important to get in the first few hours if the infection is bad enough. But what is bad enough, and how do I know if I get it, you may be asking. Hopefully, you will never have to worry about cholera — at least not in the industrialized world. Effective sewer systems and water treatment processes have for the most part eliminated the presence of cholera in the US and Europe, although the bacterium can exist in these areas. Some people get cholera from eating raw seafood from the Gulf of Mexico, but the chances for that are fairly low, so I don’t want you to panic. I write about cholera because of the relationship between cholera (and other tropical diseases) and a warmer world.

Cholera is commonly associated with higher sea temperatures.

From the Environmental Protection Agency’s page on climate change:

…algal blooms could occur more frequently as temperatures warm — particularly in areas with polluted waters — in which case diseases (such as cholera) that tend to accompany algal blooms could become more frequent.

Also, warmer waters accompany rising sea levels, which could flood areas and contaminate water meant for agricultural uses and drinking water. Higher need for potable water due to increased population may also strain sewer systems and treatment plants efficacy. I promise I am not trying to scare you, but a warmer climate can change the playing field when it comes to combating pandemics like cholera.

Here is a cute little rule of thumb when choosing water and food when traveling, or when the US turns tropical.

Boil it, cook it, peel it, or forget it.

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This is post is part of a series that is looking at the impending danger of tropical diseases moving into temperate areas. The cause of this migration is the actual movement or rather expansion of the tropics themselves, thanks to global warming and climate change.

Dengue Fever

Dengue fever is also spread by a mosquito, much like malaria. In dengue fever’s case it is the Aedes mosquito that transmits the four different strains of the flavivirus. For the most part, dengue is not super-serial, er, i mean super serious (accidental channeling of the South Park version of Al Gore, sorry), but can become serious in two ways. Dengue is more than capable of *ahem* going viral (goodness, I am full of mischief today), that is becoming an epidemic or even worse, a pendemic; or it may become a more dangerous case of Dengue Hemorrhagic Fever. The ‘hemorr-’ prefix is not usually a good one, referring to hemorraging blood.

Dengue symptoms include severe headaches, severe muscle and joint pain, and a red rash that can cover the entire body. Sometimes there can be gastrointestinal distress (I love that phrase) as well. If the fever gets bad enough, that is when the hemorraging starts, and finally you die. Ok, that was glib, but death does occur in about 5% of untreated cases, one percent for those who do receive proper medical care.

Dengue fever breaks out in most places, and is endemic to the United States, mostly in the South. Epidemics break out here and there in tropical countries every so often, being recorded as far back at the late 1700’s. And why the 1700’s? Because that’s when Europeans colonized the tropics, and our history is Euro-centric, obviously, because I will bet you dollars to doughnuts that dengue has been around a long, long time. No matter here as I am not letting myself continue on my diatribe about “history.” Moving on…

Dengue Fever breaks out enough to affect 50 to 100 million people around the world. Only a few hundred thousand get dengue hemorrhagic fever. Usually these cases happen in the tropics, or maybe among travelers that had visited tropical climates. However, the tropical bands that circle this planet between what had traditional been the two “Tropics” of Cancer and Capricorn are spreading north and south into sub-tropical regions and those subtropical regions are likewise spreading up into temperate zones. This may not seem like a big deal to you there in Minnesota, and will hopefully never be a big deal, but just think about how much hotter and wetter your summers have been in the last twenty years? Wetter and hotter means more mosquitoes. No, but seriously, it may not be a big deal for those of you living above the 35th parallel (or south of it in the Southern Hemisphere), but things only seem to be getting hotter…

I’ll break it down for you. If it doesn’t freeze in the winter, the terrori– mosquitoes win.

By the way, the Centers for Disease Control think that dengue is pretty dengue serious. Oh my, what is wrong with me today?

In 2005, dengue is the most important mosquito-borne viral disease affecting humans; its global distribution is comparable to that of malaria, and an estimated 2.5 billion people live in areas at risk for epidemic transmission (Figure 4). Each year, tens of millions of cases of DF occur and, depending on the year, up to hundreds of thousands of cases of DHF. The case-fatality rate of DHF in most countries is about 5%, but this can be reduced to less than 1% with proper treatment. Most fatal cases are among children and young adults.

Many more cases probably go unreported each year because surveillance in the United States is passive and relies on physicians to recognize the disease, inquire about the patient’s travel history, obtain proper diagnostic samples, and report the case. These data suggest that states in southern and southeastern United States, where Ae. aegypti is found, are at risk for dengue transmission and sporadic outbreaks.

Here’s Figure 4.

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Yesterday, I started a series of posts on tropical diseases that are spreading into areas that until recently had not been present or at least not typically present, like North America and Europe. In short, tropical zones are spreading into previously temperate areas and bringing tropical diseases with them.

Malaria kills over one million people a year, mostly in tropical areas like Sub-Saharan and Equatorial Africa. However, according to the Centers for Disease Control, 300 to 500 million people suffer from malaria every year. Symptoms include fever, chills, headaches, vomiting, and sometimes seizures in young children. The earlier that malaria is diagnosed and treated, the better the chances for a full recovery. But as malaria is not seen in such places like Michigan and New Jersey, the symptoms are often mis-diagnosed, meaning that the disease will not be treated properly and the chances of more severe consequences increase. When malaria is left untreated, victims can experience kidney failure, cardiovascular collapse, and slip into a coma. People that don’t live in malaria-prone areas are at higher risk as they have no immunity to the disease. Pregnant woman, children, and anyone with a compromised immune system are also at increased risk of more severe cases of malaria.

Malaria is spread by Plasmodium (Plasmodium falciparum or Plasmodium vivax) parasite carried by the Anopheles mosquito from human host to human host.

This is what is looks like when the parasite starts attacking your red blood cells.

Malaria can be treated with several drugs, and treatment should start within 24 hours of the appearance of the first symptoms. So you can see why proper diagnosis is so important. However, scientists are finding that plasmodium parasites are becoming resistant to many of the older drugs currently on the market mostly in poorer countries and areas of the world afflicted by malaria. Malaria prevention by way of mosquito control is touted as the best way to combat the disease, but now that the range for the anopheles mosquito is spreading, this is becoming increasingly difficult.

Here is a map that shows the classic range of malaria.

But as the world warms, and winters become milder, warmer, and wetter, the necessary cold temperatures that kill off the mosquito populations in temperate areas are not quite effective and becoming less so in the fight to keep malaria at bay in temperate North America and Europe. Malaria had been endemic to North America, but stringent preventive measures have effectively wiped out the disease in the US. But with the looming danger of global warming trends, malaria may be posed to once again be endemic in the US.

By the way, quinine is one of the oldest medicines for treating malaria. Quinine comes from the bark of the cinchona tree, native to South America. Quinine was first made into a powder by the French for ingestion, but really hit its mark when the British mixed it with soda water (and gin, of course). You could say that quinine is what made colonization of certain parts of the world possible, as Africa was once called the “white man’s grave.”

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You may remember years ago when SARS broke out and with it fears that this disease could spread with human hosts as they traveled across the globe? Well, it is true that diseases can spread through the human hosts in this age of trans-global travel, and if that happens, it can be dangerous. But something else is happening to spread diseases that just don’t exist everywhere.

Tropical diseases don’t usually show up in places like Europe and North America, but they are starting to, and this problem may get worse before it gets better.

At the heart of the problem is that it is the tropics themselves that are on the move, and with them come certain insect-borne diseases such as malaria and dengue fever.

I had written on tropical diseases moving into Europe back in January. And now, I have run across more bad news and this time it is coming from the World Health Organization. The Nobel-prize winning Intergovernmental Panel on Climate Change (IPCC) has already noted that more and more people will be afflicted by tropical diseases, and why? Global warming and climate change. The warmer parts of the world, where many lethal diseases thrive, are expanding their range into formerly temperate regions. And with milder winters, insects and other disease-carrying organisms are not killed off during winter months, and thus expanding their range every year.

A study published last December in Nature Geoscience reported that tropical zones are moving at a much faster rate than computer models had predicted.

Scientists have found that, during the past 25 years the equatorial region classified as climatologically tropical has expanded polewards by about 172 miles which has meant that a further 8.5 million sq miles of the Earth are now experiencing a tropical climate, compared to 1980.

The study was carried out by Dian Seidel of the US National Oceanic and Atmospheric Administration in Washington, her colleagues from the National Centre for Atmospheric Research in Boulder, Colorado, and the universities of Washington in Seattle and Utah in Salt Lake City.

They found that, during the past quarter-century, the area defined as tropical, based on a list of five recognised climatological criteria, has moved further north and south by about 2.5 degrees of latitude, or about 172 miles in total in both directions. That is greater than the predicted shift of 2 degrees by 2100 predicted under the “extreme scenario” envisaged by the Intergovernmental Panel on Climate Change. –The Independent

What is a “tropical” region? Of course, we think of palm trees and mai tais, but that is really not what we are talking about when we discuss tropical diseases. Tropical regions receive more sunlight than anywhere else. If you need a simple definition, you can use a globe and check out the area between the “Tropics” of Cancer and Capricorn. But scientifically-speaking, the tropics are wetter. Warmer air can hold more moisture, and the tropics have the hottest air thus the wettest air. As you move away from the tropics, air cools and thus the “sub-tropics” have less moisture in the air. Meanwhile, that moisture has fallen somewhere before hitting the sub-tropics. So not only is the air in the tropics wet, but there is an awful lot of precipitation in the tropics. That much water can create very inviting environments for such disease-carrying insects like the mosquito.

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