Tropics on the Move - Diseases Too

Last January we wrote about the creeping consequences of climate change. On this topic, some predictions are becoming realities. One such prediction is that with climate change, the tropical zones will expand, moving upward toward the poles, and a dangerous side effect of that tropical expansion will be the movement and migration of tropical diseases, such as Dengue Fever and Malaria, to parts of the world that have never been affected by them.

This past summer, the first outbreak of a tropical disease was reported in Italy. More than 100 people were afflicted with chikungunya (CHIKV), a relative of Dengue Fever, in a small village of 2,000 called Castiglione di Cervia along the eastern Italian Coast near Ravenna. That's along the northern east Italian Coast. The story of this previously unknown disease in Europe was not widely reported until December in the International Herald and the New York Times.

Who would have thought that on your dream vacation to Italy you'd have to get malaria shots? It is not quite that bad... yet.

But still, the outbreak of chikungunya is troubling. Especially as researchers and scientists have predicted that this expansion of the tropical belt would most likely be accompanied by an expansion of tropical diseases.

From December of last year, The Telegraph reported that the tropics have been expanding towards the poles for the last 25 years.

The rate of expansion of the tropics in the past 25 years is greater than computer models expect to occur this century even with climate change, according to a paper published as talks on climate change get under way in Bali, Indonesia. The tropical belt, defined by typical rain and wind patterns within the band from the Tropic of Cancer to the Tropic of Capricorn, has expanded by about 2.5 degrees latitude, or about 185 miles, over the past quarter century, according to the paper to be published in Nature Geoscience. -- Telegraph
Further along in the same article, Barry Brook, a professor of climate change at the University of Adelaide, explains that there are two reasons to worry about the expanding tropics. Although he specifically mentions Australia, the implications of expanding tropical belts can be applied elsewhere around the world.
First, as the tropical zone expand, the mid-latitude weather systems are pushed further polewards. These westerly systems bring rain to Australia's southern coastline. As they shift southwards, progressively more rain is dumped over the southern ocean, instead of over continental Australia where we need it. Second, an expansion of tropical pathogens and their insect vectors is almost certainly sure to follow the expansion of tropical zones. As subtropical cities such as Brisbane, and even those that are currently only marginally sub-tropical, like Sydney, will become increasingly suitable for diseases such as dengue fever, Ross River virus and perhaps eventually malaria. -- Telegraph
Previous range of the chikungunya virus
Getting back to the issue in Italy, more information about the chikungunya outbreak can be found on Eurosurveillence (scroll down the linked page, as the first half talks about HIV). According to this source, more outbreaks were reported in surrounding communities, the last such outbreak occurring in September. The culprit in the transmission of the chikungunya virus is the tiger mosquito (Aedes albopictus), previously confined to such tropical areas as countries bordering the Indian Ocean. Officials blame the outbreak on two factors. One, that the tiger mosquitoes are not only found in Northern Italy (as well as France and even Switzerland), but are thriving in the area. The second factor, and the spark that set it all ablaze, was a man who had traveled to India and brought the chikungunya virus back to Castiglione di Cervia. The disease was then spread by the mosquitoes. The spread was stymied after wide-spread efforts to contain the mosquitoes, namely insecticides and eliminating standing water in which the mosquitoes breed. The outbreak ended with the onset of colder, non-mosquito-friendly weather as well.

However, last summer's outbreak of a tropical disease may be a bad omen of things to come. What will happen this summer when the weather is again conducive to mosquito reproduction? Has the chikungunya the ability to winter in some mosquito eggs, and will it have a resurgence? Will it be able to spread even farther into Europe, or the other places around the world that have seen the introduction and survival of the tiger mosquito?

As if the news of chikungunya is not enough to worry health officials in Italy, another tropical disease seems to be moving into the Mediterranean. Eurosurveillence has also reported that Ostreopsis Ovata has been found in increasing numbers in the Adriatic since the first outbreak of the toxic algae in 2005 that can aggravate the respiratory system and cause fever. This algae doesn't seem to be lethal, but it did require that 20 percent of those affected be hospitalized, as well as many beaches having to be closed during the summer months.

Now, it is true that other such outbreaks of tropical diseases have occurred in Europe over the centuries. Dengue and Yellow Fever have been imported at times and caused some trouble in Spain, Portugal, France and even England. Athens lost over 1,000 people to Dengue Fever in the late 1920's during an outbreak. While these cases were a bit more isolated and usually caused by people bringing the disease into Europe and being spread by the normal mosquitoes, the current mood in Europe regarding such tropical diseases is that global warming is creating an atmosphere in which the insects that spread the diseases can thrive and possibly survive through the winter. The summer of 2008 will be a test to see if the chikungunya is a one-time epidemic or a new public threat.

And please, don't let me lead you to think that only Europe and other more Northernly climes are seeing tropical diseases move in to the neighborhood. Some areas of Africa are also seeing an influx of diseases that were not present before. Higher altitudes in mountainous areas of Africa are experiencing outbreaks of low-altitude diseases, such as Malaria with increasing frequencies.

Many medical and environmental experts attribute the spike in malaria to climate change, in the form of warmer temperatures and variations in rainfall patterns. "We are now finding malaria in places that we did not expect to find it, particularly the highland regions that used to be too cool for malaria," said Dorothy Memusi, deputy director of the Malaria Division in Kenya's Ministry of Health. -- National Geographic News

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  • Posted on Jan. 18, 2008. Listed in:

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