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Dengue Fever - A Sign of Things to Come?

Last summer the residents of Castiglione di Cervia, a small village in northern Italy, were suddenly stricken by a temporarily debilitating disease that was unknown to local medical authorities.  Following the death of several villagers, and the subsidence of the outbreak, the disease was eventually identified as Chikungunya, a disease with symptoms similar to Dengue fever.   Both Chikungunya and Dengue fever are mosquito borne, viral diseases, previously known to  occur only in the tropics.  Its appearance in Europe is apparently due to Global Warming and the "globalization" of commerce and travel. 

Ultimately the source of the Castiglione di Cervia epidemic was found to be a visitor to the village who had recently returned from a trip to India and whose blood was carrying the Chikungunya virus.

Northern Italy had been largely free of mosquitoes until it was recently invaded by large numbers of tiger mosquitoes, a consequence of a warming climate since winters in the region are no longer cold enough to kill the over-wintering eggs.  As the virus can over-winter in mosquito eggs, it is possible that this summer will bring additional cases, and the spread of this former tropical disease through Europe.  If not, it is only a matter of time before a similar set of circumstances occurs as the tiger mosquito now seems to have a firm foothold in Europe.

The tiger mosquito (Aedes albopictus)  was first found in the United States in the mid-1980's and has since spread throughout the southeast and lower mid-west states, ranging westward to southern Texas, and rapidly expanding northward along the Atlantic Coast.   Research has demonstrated that its rate of population growth rapidly increases with increasing temperature.  As the tiger mosquito thrives in a number of habitats and can reproduce in diverse moist locations such as tree bark in addition to water in discarded cans and other containers, control and eradication programs have failed.  In addition to Chikungunya, tiger mosquitoes are a successful vector (carrier) of other diseases including Dengue fever, encephalitis, yellow fever and dog heartworm.

The tiger mosquito is an extremely aggressive mosquito, and usually out-competes and replaces native mosquito populations.  In addition to displacing native species, it also appears to have displaced the closely related yellow fever mosquito (Aedes aegypti), another recent invader from the tropics.

Brazil is currently undergoing an major epidemic of Dengue fever that is so severe that the government has mobilized the military to assist with the housing and care of the sick, primarily in the City of Rio de Janeiro where the medical facilities are being overwhelmed.  Today the Rio de Janeiro reported over 60,000 cases of Dengue hemorrhagic fever, one of the more severe variants of Dengue.  Children are being especially hard hit.

It is easy to imagine the scenario of a tourist returning to a major North American city (for example: Atlanta, GA) after an overnight stop in Rio de Janeiro where she suffered a mosquito bite.  After several days, our tourist develops a fever and muscle and joint ache.  After a few days of being miserable, she seeks medical attention, and is rapidly diagnosed as having a case of the flu.  In the meantime our tourist, who enjoys being outside in the sun, has been bitten by a few more mosquitoes. 

So far, nothing at all out of the ordinary, but lets assume that additional people are starting to seek out their doctors, again with fever, muscular and joint soreness, but some also exhibiting a rash.  Soon we have a number of people, each seeing different physicians, and exhibiting symptoms which are not entirely consistent.  And since most of the cases appears to occur in isolation, there is no evidence of a communicable disease.   It is going to take a lot of sick people before the medical community recognizes an unusual commonalty of symptoms  starts to realize that they have a real concern on their hands.   The situation is additionally complicated by the fact that all of the physicians have probably seen patients with a fever, joint and muscle pain, and a rash.  But probably none, or very few of the physicians, have ever seen Dengue fever. 

As there is no lab test for Dengue fever it can only be diagnosed "clinically" by the assemblage of symptoms.  There is also no "cure", or vaccine, for Dengue fever, the only treatment is "supportive".  Basically, you treat the symptoms and keep the patient hydrated, try to keep a very sick person alive, and let the disease run its course.  There will be moralities, especially among the very young, the old, and the weak.

By the time that Dengue fever is diagnosed, our hypothetical city, Atlanta, would have a full-blown public health crises on its hands, with its medical facilities overcrowded with the most serious cases, and its medical personnel stretched thin.  Meanwhile, the region is filled with an ever increasing number of disease-bearing mosquitoes, and new cases are occurring daily.  The only way to curtail the epidemic is to stop people from being bitten by tiger mosquitoes.  A public education program has to be implemented, sprays and repellents distributed and other public protective steps taken.  And, while no program has yet been able to eradicate the tiger mosquito, reduction of their numbers would certainly reduce the number of bites and new cases of Dengue fever.  But to be at all effective, a very massive program of treating every bit of water and moist location with an insecticide would be required, and every old can, bottle, tire, flower pot, and anything else that might briefly hold water would have to be cleaned up. The planning and implementation of these programs require time and money.

If for no other reason than the ending of mosquito season, the epidemic would eventually run its course.  However, there is now a pool of the Dengue fever virus in the mosquito population and the disease would most likely reoccur each succeeding year.

This scenario is an illustration of what we can expect as consequence of Global Climate change.   Biological species will migrate, and occupy new territory, as a result of changing climate; and, some of these species will be disease vectors, or carriers and transmitters of disease.  The vectors, such as the tiger mosquito, can become widely established in their new territory, and not be recognized as a public health problem, until an alternate disease host - such as our Atlanta tourist - arrives on the scene.  Since our health professionals will not be familiar with the new disease, it may be some time before it is properly diagnosed and treatment can be initiated - if in fact, the proper medications are even available.  In addition, the only effective means of controlling the spread and occurrence  of a vector-borne disease requires control of the vector itself, which time has proven to be a major, time consuming task.

As the result of global warming, and the globalization of trade and travel,  the temperate regions of the world now have been invaded by an assemblage of new, unknown disease vectors for both plants and animals.

Truly we are sitting on an agricultural and public health time-bomb.  Will we have the wisdom to act in time?

Do we have the infrastructure in place to provide supportive health care to large numbers of seriously ill individuals?  If our hospitals are overflowing are plans in place to utilize schools, armories, and other public facilities?  If a large proportion of our population is ill, are we prepared to keep critical services functioning?  Do we have the systems in place to provide backup support to our health care professionals in the timely identification and diagnosis of hither-to inexperienced diseases; and in the implementation of the proper public health care procedures?  These are some of the critical questions that each community must address in order to prepare for climate change.

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