Effects of Climate Change on West Nile Virus

West Nile Virus is a vector borne zoonotic virus that belongs to Genus Flavivirus. Viruses of Genus Flavivirus are commonly found in both tropical and temperate regions of the globe. West Nile Virus was first discovered in East Africa in 1937. It is transmitted through one species of Mosquito to the birds, and then, occasionally, to the humans. In mid 1990s, the spread of the virus was only sporadic and was classified as being of less significant risk to humans. However, this was until 1994, when there was an outbreak of the virus in Algeria. Since then, West Nile Virus has been reported in other parts of the globe. Nonetheless, the first case in North America was reported in New York in 1999. Within a period of 4 years, the virus had spread across the entire America continent including the USA, Canada, Latin America, and the Caribbean Island (Bernard, Kramer, 2001).

West Nile Virus was reported for the first time in North America in 1999. However, the ways the virus was introduced in the region remain unclear. Since then, numerous hypotheses have been deduced to explain this unusual phenomenon. It has been hypothesized that migratory birds were the main vector responsible for introducing the virus in the region. In addition, anomalous in the weather conditions have been found to provide favorable condition for its amplification. Numerous researches that have been conducted on the West Nile Virus in the different regions of the world including the USA, indicate that weather conditions, man-made modification of the environment, and mosquitos influence lifecycle and transmission of West Nile Virus. For instance, the urban mosquitoes lay eggs in the turbid water produced in the cities. However, normal rainfall washes these areas; hence, prevent the stagnant water from turning grey. As a result of the global warming, drought spells permit the organic matter to turn turbid; thus, provide the Culex Pipien’s larva with nutrients. Once this mosquito larva get hatched from the water, they bite an infected bird and eventually, transmit the virus to the humans through bites (Brandt, Martyak, Westhoff, Kang, 2004).

West Nile Virus is spread to the humans and other animals through mosquitoes that have bitten infected birds. It is now evident that climate is one of the main variables in transmission of the virus from the vectors to a human being. Therefore, many researches have been conducted in order to explain the role of the climatic change on the lifecycle and development of the virus. According to the recent statistics from the Texas Department of Health service, 586 illness cases resulting from WNV have been reported. Furthermore, 21 of the cases have resulted to death. In 2008, the researcher from the University of California reported that higher temperatures resulting from the global climate change facilitated the development of a new strain of West Nile Virus, the virus strain that has invaded and spread sporadically in the different parts of North America. Warmer temperatures have been considered to be a greater advantage for the life cycle development of a new strain of West Nile Virus (Kilpatrick, Kramer, Jones, 2006).

According to the studies, discovery of West Nile Virus in Uganda has led to the discovery of the two new viruses: Japanese and St. Louis encephalitis; furthermore, the effects of droughts and summer elevated temperatures on the incubation period of mosquito of St. Louis have shown some correlations. Although high temperatures are often lethal to mosquitoes, they have been found to accelerate the development of West Nile Virus. The relationship between climate change and West Nile Virus has also been established in other studies, which have found that weather changeability influenced by the climatic instability has contributed to the occurrence of West Nile Virus in North America. The climate conditions experienced for the last six years have enabled the development of WNV and other epizootic viruses (Epstein, Defilippo, 2001).

In 2002, incidents of West Nile Virus were reported in New York, Chicago, and Toronto in North America. However, Montreal region was not impacted with the same level of virus, as compared to the above mentioned cities. This is despite the city being located within the same region with similar climatic conditions. In Montreal, only 21 cases and 3 deaths instances were reported, while hundred of cases were reported in the neighboring states of New York. The West Nile Virus’ cycle often relies on the mosquitos’ vector and interplays with reservoir and wild birds, as well as with the dead-end host, such as a human being. Human being develops the clinical disease within 2-6 days of incubation. Since the occurrence of West Nile Virus in New York City, the virus has sporadically spread to North American states, such as California, and some parts of Canada. The rapid and sporadic spread of the virus after the warm seasons has supported the opinion that climatic changes play a critical role in the spread and development of West Nile Virus. Therefore, understanding the ways the weather conditions aid the virus would be crucial in the control efforts.

Similar to St. Louis encephalitis in the USA and malaria in the tropical regions of Africa, rise in global temperatures has influenced the distribution of West Nile Virus in the USA.  High temperatures in the western states have been correlated to the spread of West Nile Virus and to the increase in the level of the mosquito infectivity. In 2002, there was a high caseload of transfer of virus from the secondary to the primary vectors in the Northeastern metropolitan. High temperatures resulting from the global climate change play an influential role to the mosquitos that carry West Nile Virus. This is because higher temperatures have been found to increase the viral load carried by mosquitoes. In addition, the overall incubation period has been found to reduce, as a result of the elevated temperatures (LaDeau, Kilpatrick, Marra, 2007).

In the different studies, the influence of precipitation on the development of West Nile Virus and other vector borne diseases remains unclear in the USA. The regional trend in the USA indicated that prior drought played a critical role to the outbreak of West Nile Virus in 1999. However, other subsequent studies have been erratic, since they provide both negative and positive associations with other vector borne diseases and rainfalls. Studies have indicated that the population of West Nile Virus vector has decreased and increased after a period of high precipitations depending on the geographical location.

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According to the recent climate change reports from IPCC, it is anticipated that the weather and climatic conditions in North America will change considerably in the few decades. The climatic change will include elevated levels of precipitations as rain, as opposed to snow, shorter winters, and increase in temperatures. In addition, it is predicted that the frequency of the heavy rainfall will increase. Since high levels of precipitations and temperatures have been found to increase the infection risk associated with West Nile Virus, such climatic changes are expected to increase the complexity and burden associated with West Nile Virus in the future (Mackay, 2008).

Numerous investigations on the role of temperature, precipitation, and humidity on the incidence of West Nile infections reported human cases. A positive correlation between the temperature increases before the onset of the symptoms has been found. Furthermore, high rainfall levels were also found the have a signification connection with incidence of West Nile Virus reported in the same period. Gradual increase in the levels of temperature has also been found to increase the risk of infectivity. This is because mosquito vectors carry high viral load during the warm seasons. Therefore, as the global temperatures increase gradually as a result of the climatic change, the incidence of West Nile Virus is anticipated to increase.

Heavy precipitations, especially during the heavy rainfalls season, have been found to increase the mosquito population. This implies that heavy rainfall leads to a subsequent increase in precipitation levels; hence, influences the transmission of West Nile Virus in a distinctive manner. The influence of heavy rainfall on the prevalence of West Nile Virus incidents indicates that increase in the rainfall levels over the last few years have subsequently increased the interaction between humans and chances of infectious bites. Previous studies indicated that heavy rainfalls essentially kindle the incidents of the disease through the increase of humidity, which prompts the mosquito vectors to seek hosts.

Since the metrological occurrence, such as temperatures and precipitations resulting from the global climate change, evolves over long periods of time, the influence of climate change on the spread of West Nile Virus utilizes comparison studies. A study conducted in 1999, when the first incidence of WNV was reported, was essentially superficial in relation to the influence of the climatic change. However, subsequent studied have noted a considerable increase in the prevalence of virus as climate changes. Although many factors influence the occurrence of West Nile Virus. Recent studies clearly indicate that there has been a gradual increase in the levels of humidity, temperatures, and rainfalls across the USA. This has momentarily increased the quantity of incidents of West Nile Virus regardless of the location and season. This indicates that as the climatic conditions continue to change, West Nile Virus will spread and morbidity will continue to increase (Petersen, Marfin, 2003).

According to the recent environmental reports from Intergovernmental Panel on Climate Changes, it is indicated that most zoonotic diseases are often sensitive to the climate changes. The strain of West Nile Virus that was first reported in the USA in 1999, requires higher temperatures in comparison to other strains. It is also evident that the great transmission of West Nile Virus in the United States occurred during the summers of 2002 to 2004, when the temperatures were above averages. Laboratories’ investigations on the development of West Nile Virus on the Culex Mosquito have shown higher correlation with high temperatures reported in the different parts of the USA. In addition, climatic changes have also influenced the migratory activities of the birds, which also provides a pathway for the spread of West Nile Virus. The recent studies indicate that climatic change has influenced the migratory patterns of the birds between the US and Canada (Epstein, 2005).

St. Louis virus that is closely related to West Nile Virus has also been found to occur during hot and warm seasons, when the environmental conditions necessitate transmission through the reduction of the incubation periods. In New York City, more than 25, 000 cases resulting from West Nile Virus have been reported since 1999. In addition, thousands of birds have been exterminated by the infection. In the New York City, the mosquitos that is likely to carry the infection are those, which breed in the natural and artificial areas, such as discarded containers and ponds. The quantity of mosquito species, such as Culex Pipiens, Aedes albopictus, and Culvex restuans, is expected to increase, as the levels of summer temperatures and precipitations increase in New York due to the climate change. Therefore, the general human risk exposure risk to WNV is anticipated to increase in New York City and other states; especially, as the weather becomes wetter and warmer. In short, health care systems in the USA and the whole North America will need to expect a shift in prevalence of West Nile Virus due to the climate change. In order to respond effectively, there is a need to devise effective mechanisms across the USA in order to evade future epidemics (Craven, Roehrig, 2001).

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In conclusion, it is evident that climatic change is an issue that needs concerted efforts to tackle, since it has severe consequence to both environmental and human health. Climate change now poses a considerably high risk to the human health through the increased exposure and vulnerability. Global warming is now a world crisis. Extreme weather conditions, increase in temperatures, and precipitation, create an ideal breeding and growth environment for much infectious diseases, such as West Nile Virus. Few decades ago, west Nile Virus was considered being of no risk to humans. However, due to the climatic changes, West Nile Virus, as well as other diseases, has become a threat to the existence of humans. As resulted of current and projected global warming trends, North America will essentially experience the reemergence and subsequent increase in the spread on West Nile Virus. In response to the anticipated change, health care systems will be required to devise the new mechanisms that are capable of adapting to the rapidly changing environment and of establishing vaccines to curb the spread of the virus. This will effectively prevent the re-emergence of West Nile Virus in the region. Vaccine will be essential in the region, because large sections of the northern population lack immunity; most infectious diseases have already been eliminated in the region. In order to prevent the spread of West Nile Virus, there is a need of concerted efforts between health officials, environmental specialist, and the general public. Without concerted efforts from the global population, climatic change and its subsequent health effects will eventually wipe out the humankind (Campbell, Marfin, Gubler, 2002).


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