Creeping Consequences - Mosquitoes and Ticks

Near the end of 2005 the Center for Health and the Global Environment released a study called 'Climate Change Futures', that tries to forewarn the world of some of the impending health and economic costs of global warming. Among the featured case studies were a couple of our rather unpopular six-legged 'friends' - the mosquito, and the tick.

Although AIDS attracts the greater media attention, mosquito borne malaria is the bigger killer - reportedly taking the lives of 3,000 children in Africa every day. I'll repeat that, 3,000 per day - and that's just children, and just Africa. Although Africa has by far the greatest occurance of the disease (around 75% of all occurances), it's also present in tropical regions across the globe. Beyond mortality, the economic impacts of malaria are immense, in lost productivity as well as the direct costs of treatment.

Although a daily nightmare in Africa, in the North malaria barely gets a mention. But, as the world warms, this may change.

Climate constrains the range of malaria transmission while floods (and sometimes droughts) provide the conditions for large outbreaks. Warming, within the viable range of the mosquito (too much heat kills them), boosts biting and reproductive rates, prolongs breeding seasons and shortens the maturation of microbes within mosquitoes.
Current Malaria Distribution Range
For malaria transmission to occur, a mosquito must take a blood meal from someone with malaria, incubate the parasite, then bite an uninfected person and inject the parasite. Warmer temperatures speed up the maturation of the malarial parasites inside the mosquitoes. At 20°C (68°F), for example, Plasmodium falciparum malarial protozoa take 26 days to incubate; but, at 25°C (77°F), the parasites develop in half the time (McArthur 1972). Anopheline mosquitoes that can transmit malaria live only several weeks. Thus warmer temperatures permit parasites to mature in time for the mosquito to pass it on to someone previously uninfected.... - Climate Change Futures, Final Report p.32 (5.4mb PDF)

The geographic distribution and activity of insects are exquisitely sensitive to temperature changes. Today, insects and insect-borne diseases are being reported at high elevations in East and Central Africa, Latin America and Asia. Malaria is circulating in highland urban centers, such as Nairobi, and rural highland regions, like those of Papua New Guinea. Aedes aegypti, the mosquito carrier of dengue and yellow fever, has been limited by temperature to about 1,000m (3,300 ft) in elevation. In the past three decades it has been found at 1,700m (5,610 ft) elevation in Mexico and 2,200m (7,260 ft) in the Colombian Andes (Epstein et al. 1998). - ibid p.33 (5.4mb PDF)

Measurements drawn from released weather balloons, satellites and ground thermometers all show that mountain regions are getting warmer. Between 1970 and 1990 the height of the freezing isotherm (permafrost or permanently frozen ground) climbed approximately 160m (almost 500 feet) within the tropics, equivalent to almost 1°C (1.8°F) warming (Diaz and Graham 1996). Exemplifying this trend, plants are migrating to higher elevations in the European Alps, Alaska, the US Sierra Nevada and New Zealand (Pauli et al. 1996). These insect and botanical trends, indicative of gradual, systemic warming, have been accompanied by the accelerating retreat of summit glaciers in Argentina, Peru, Alaska, Iceland, Norway, the Swiss Alps, Kenya, the Himalayas, Indonesia, Irian Jaya and New Zealand (Thompson et al. 1993; Mosley- Thompson 1997; Irion 2001). - ibid p.34 (5.4mb PDF)

Under CCF-II we project intensification of malaria transmission throughout highland regions in Africa, Latin America and Asia, with continued transmission in lowland regions. In addition, malaria could suddenly swell in developed nations, especially in those areas now bordering the margins of current transmission. This could present severe problems in southern regions of Western and Eastern Europe and in the southern US. - ibid p.39 (5.4mb PDF)

West Nile Virus, also a mosquito borne disease, has already made inroads into western territory - in fact, it wasn't seen in the U.S. before 1999:
West Nile virus has been described in Africa, Europe, the Middle East, west and central Asia, Oceania (subtype Kunjin), and most recently, North America.

Recent outbreaks of West Nile virus encephalitis in humans have occurred in Algeria (1994), Romania (1996 to 1997), the Czech Republic (1997), Congo (1998), Russia (1999), the United States (1999 to 2003), Canada (1999–2003), and Israel (2000). - Wikipedia

The United States had never had a documented case of West Nile before it was introduced from overseas in 1999. That year, New York City experienced its driest and hottest spring and summer in a century. Stagnant and polluted pools of water throughout the city became the perfect breeding grounds for the mosquito vector, Culex pipiens. - People's Weekly World

West Nile virus (WNV) is an urban-based, mosquito-borne infection, afflicting humans, horses and more than 138 species of birds. Present in the US, Europe, the Middle East and Africa, warm winters and spring droughts play roles in amplifying this disease. To date, there have been over 17,000 human cases and over 650 deaths from WNV in North America. - Climate Change Futures, Executive Summary (600kb PDF)

Now we turn to an insect that is guaranteed to make even the most macho of individuals squirm - the tick - a creature that brings Lyme disease with it.
Lyme disease most often presents with a characteristic "bull’s-eye" rash, called erythema migrans, surrounding the attached tick. The initial infection can be asymptomatic, but is often accompanied by fever, weakness, and head, muscle and joint aches. At this stage, treatment with antibiotics clears the infection and cures the disease. Untreated Lyme disease can affect the nervous system, the musculoskeletal system or the heart. The most common late manifestation is intermittent swelling and pain of one or several joints, usually large, weight-bearing joints such as the knee. Some infected persons develop chronic neuropathies, with cognitive disorders, sleep disturbance, fatigue and personality changes....

Lyme disease is the most prevalent vector-borne disease in the continental United States. Lyme was discovered in 1977 when arthritis occurred in a cluster of children in and around Lyme, CT. Since that emergence, Lyme disease has spread throughout the Northeast of the US, two north-central states (Minnesota and Wisconsin) and the Northwest (California and Oregon). In these areas, between 1% and 3% of people who live there become infected at some time.

Lyme disease is also common in Europe, especially in forested areas of middle Europe and Scandinavia, and has been reported in Russia, China, and Japan....

Climatic variation largely determines the maintenance and distribution of deer tick populations by regulating off-host survival....

The northward spread of warming conditions and warmer winters creates ideal conditions for the northward spread of Lyme disease into Canada, with continuing transmission in most of the regions with transmission currently. In some areas the abundance of ticks may increase as well, intensifying transmission. Expansion of the range of Ixodes ricinus in Sweden has already been documented and the northern migration is correlated with milder winters and higher daily temperatures. - Climate Change Futures, Final Report p.45, 46 (5.4mb PDF)

Aside from the personal element of suffering the diseases bring to us, the economic costs, although hard to accurately quantify, are immense. Referring to Lyme disease, the report states the following:

The productivity losses associated with chronic disabilities affect individuals, communities, work places and health insurance companies.

One analysis (Vanderhoof and Vanderhoof-Forschner 1993) conservatively estimated costs per case at about US $60,000. Based on an annual mean incidence of 4.73 cases of Lyme disease per 100,000 population, a later decision analysis model (Maes et al. 1998) yielded an expected national expenditure of US $2.5 billion (1996 dollars) over five years for therapeutic interventions to prevent 55,626 cases of advanced arthritis, neurological and cardiac disease. These figures may underestimate the true costs of the long-term disabilities incurred. - Climate Change Futures, Final Report p.45, 46 (5.4mb PDF)

The report does a very good job at making the connection between climate instability and the explosive nature of diseases very obvious.
From 1976 to 1996, the World Health Organization (1996) reports the emergence of over 30 diseases “new” to medicine, including HIV/AIDS, Ebola, Lyme disease, Legionnaires’, toxic E. coli and a new hantavirus; along with a rash of rapidly evolving antibioticresistant organisms. But the resurgence and redistribution of infections involving animal vectors, hosts and reservoirs — mosquitoes, ticks, deer, birds and rodents — reflect changing ecological balances and an altered climate.... - Climate Change Futures, Final Report p.33 (5.4mb PDF)
This is in direct relation to the increase of extreme weather events around the world:

If you don't have time to read the full report (5.4mb 126-page PDF), take a look at the executive summary (600kb 14-page PDF).


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  • Posted on Jan. 16, 2007. Listed in:

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