Malaria Emergence in Different Regions in the World - Research Paper Example

Causal Relationship between Emergence of Malaria and Changes in Natural Environment Introduction Malaria is caused by a protozoan parasite that infects both mammals and mosquitoes (Florens et al., 2002). Of the different species of the parasite, P.falciparum is the most life-threatening, causing over 1 million deaths annually and killing a child every 30 seconds. Malaria is most prevalent in Africa and puts about 40% of the world at risk (Florens et al., 2002). Malaria is transferred from mosquitoes to mammals and from mammals to mosquitoes through mosquito bites. It is primarily spread and carried by the Anopheles mosquitoes (Florens et al., 2002). Once transferred by a malaria carrier, the parasite moves to the liver within 30 minutes and reproduces at a rapid speed. Once liver cells are laden with the parasite, they burst and release the parasite into the bloodstream where it enters blood cells and starts to reproduce, causing the red blood cells to burst. Then the parasite exits the red blood cells and infects other blood cells. This process depletes the patient’s oxygen supply and induces fever. Meanwhile, dormant parasites enter the bloodstream, waiting to be consumed by non-infected mosquitoes and spread the infection. There are about 40 different species of Anopheles mosquitoes. All breeding in stagnant water, these mosquitoes also complete the first stages of their life cycle (from an egg to a larva and finally to a pupa before maturing to an adult) in water, ponds, and puddles. An incubation period of 10 to 21 days is required for an infected mosquito to transmit malaria parasite. Important factors of malaria outbreaks are climatic and landscape features and conditions which are crucial to the anopheles mosquitoes’ survival. Critical requirements for malaria to develop and spread are, first of all, temperatures above 15°C; the incubation period can be shortened at higher temperatures. The mosquito must also survive the incubation for the parasite to develop. Stagnant water is another important factor required for the anopheles mosquitoes to develop through its larva stage. Besides, a sufficient number of infected anopheles mosquitoes is also required for transferring malaria to human populations and emerging as a serious infectious disease. Changes to natural environments may alter these important factors, making them more suitable for malaria development and transmission. In this paper, irrigation of the Thar Desert in India, abnormal occurrence of drought in highlands of Irian Jaya, and deforestation in the Amazon basin or rainforest are cited as three instances to prove the causal relationship between changes in the natural environment and the emergence of malaria. I. Irrigation in the Thar Desert and Emergence of Malaria The three man-made canals network, Gang Canal, Bhakra–Sirhind Canal Project, and IGNP Project, of India has been established in the Thar located in the Rajasthan State. As water from the Himalayas which over the years has increased ambient temperatures and humidity forming optimal conditions for successful mosquito development was introduced to the canals network it transformed the ecosystem, bringing high surface moisture, and marshes. This caused a rise in the water table and increased precipitation thus attracting numerous Anopheles species into and around the region by increasing still water that is necessary for their breeding and development of Larvae thereby leading to a noted rise in mosquito population (Sharma, 1996; Tyagi et al). Thus, the irrigation introduced and significantly increased a population of malaria vectors. As a malaria carrier, this population elevated amount of malaria in the Anopheles population by the following process: The small percentage of mosquitoes infected with malaria consumed human and mammal blood, spread malaria to these species. These species then infect uninfected mosquitoes through mosquito bites, increasing population of malaria-carrying-mosquito. As a result, a steady rise in malaria in the Anopheles population sustained malaria levels to a moderate level that ensured malaria’s continuous presence. Besides, the canal system and its water which encompasses a very large area, provided routes for malaria vectors to travel to other regions of the system thereby stabilizing continuous presence in these areas as well. Chances of eliminating the vectors in different parts of the canal system fell, sustaining a stable vector and parasite population throughout the system. As result of these major irrigation projects, Anopheles mosquitoes adopted the Thar desert as a new home. As a natural malaria vector, they also caused emergence of malaria and introduced A. stephensi, A. culicifacies, A. subpictus and A. annularis to the Thar desert. Years after the initial development in the late 1920s, the number of Anopheles species increased to seven and total Anopheles population grew to 44% of all Anopheles species in Rajasthan State, and increased to 68% when the IGNP irrigation project initiated in the early 1960s when number of Anopheles species rose to twelve. Over decades of irrigation, A. culicifacies and A. stephensi became the primary malaria vector before spreading malaria to A. subpictus . Presently, the A. culicifacies species is the main vector in the region and causes about 60 to 70% of the malaria cases in all of India that sums to be 2 to 3 million annually. The emergence spread from northernmost Sri Ganganagar district downstream and travelled to the south-western newly built districts near the IGNP regions. In effect, the irrigation attracted the malaria-carrying vector to the Thar desert, and leading to a significant emergence of about 68% of all malaria cases in India, affecting over 1 million individuals. The malaria emergence has been characterized by prevalence of Plasmodium falciparum infection, causing high morbidity and mortality. When the disease first occurred in the desert, only 10% were infected with P. falciparum. This value increased to over 80% in recent seven decades. Most of the infected near the desert were children. More gametocytes carriers were found in irrigated villages than unirrigated villages. Anopheles stephensi is most reproductively adapted in the Thar Desert and is the first malaria vector, is the most abundant carrier. Malaria is present in 38.8% of its population. (Zahar, 1990; Tyagi, 1994a). A. culicifacies was first found to be a vector in the Sri Ganganagar district, a highly irrigated area (Tyagi & Verma, 1991). Subsequently, it was found to be a malaria carrier in both irrigated and unirrigated villages (Tyagi, 1996). Anopheles nigerrimus, with 71% of its population infected with malaria, is prominently found and contacted humans during dusk as they are attracted to torches and vehicle lights. Most infections from the vectors occur during times of their maximum density. Maximum density of A. stephensi occurs in April and reaches a minimum in January. Maximum density of A. culicifacies occurs between July and September. Anopheles subpictus density increases in late June and remains high until December. In the Thar Desert, two malaria incidence peaks. The first peak occurs during the summer months between March and April, mainly caused by density increase of A. stephensi; the second peak occurs between December and January caused by A. culicifacies, and Anopheles subpictus occurring in increasing density during this period. This emergence of malaria in the Thar Desert therefore represents one of the most significant cases caused by man-made changes to natural environment. It demonstrates how human expansion and exploitation of natural resources could cause natural ecological systems to change, attracting new vector populations and eventually giving rise to the emergence of malaria in areas that were unsuitable for such infectious diseases in the past. II. Abnormal Drought and Temperature and Emergence of Malaria Malaria has been a major concern in coastal lowland of Irian Jaya (western New Guinea), a large eastern province of Indonesia. Malaria transmissions are unstable between 1000m to 1500m above sea level (asl) while low to moderate levels of seasonal malaria transmission do occur. Most malaria incidences are due to P. falciparum infection. Highlands of New Guinea with elevations above 1500m asl are, for most of the time, free of the autochonthous malaria. The cool highland temperature increases extrinsic cycle duration of the parasite to exceed the vector’s lifespan, thus preventing successful development in vector (Anthony et al., 1992). Transmissions to regions with elevations below 1500m to those above 1500m can occur depending on varying nature of terrain, socioeconomic development, and seasonality. When outbreaks occur, An. Punctulatus is the dominant vector in the highlands region. This Malaria transmission can be influenced by climatic conditions to cause transmission to higher elevations and from lowland region developed. Isolated focal outbreaks of malaria occur occasionally in the highland regions. There was an abnormal occurrence of drought and increase in temperature in the highland regions between August and December 1997, causing malaria emergence .Lowest average temperature in August for that year was 19oC while average daily temperature fluctuated above normal trends. Increase in temperature reduced extrinsic cycle of the parasite, allowing it to develop in An. Punctulatus that under normal conditions, its lifespan is too short for the parasite to complete incubation period. And this continued for a larger number of days thus leading to enhanced development as this increase speed of incubation, thereby leading to larger transfers to humans before mortality. This increased amount of malaria in vector population.. Temperature rise provided conditions more suitable for malaria to development, increasing amount of malaria in vector population. This increases infection in human population contributing to malaria’s emergence. An abnormal drought occurred between late summer and the end of the year in the same year. Amount of normal rain days and rainfall decreased by 70% and 75%, respectively. Amount of rain in highland areas decreased both in distribution and amount compared with average years. Rainfall in late July declined rapidly, causing formation of many temporary pools of standing water along stretches of steep gradient streams in unaltered natural regions of the highland. Normally, abundant rainfall causes fast-flowing water, which would be unsuitable for anopheline larvae to develop. The drought eliminated fast-flowing water and increased transitory pools. As a result, the more transitory pool of water in the natural streams permitted larval development that caused rapid rise in mosquito population to a sufficient level to sustain and intensify stable and continuous malaria transmission from lower elevations. This rise in vector population increased malaria in the vector population, and contributed significantly to the outbreak (Anthony et al., 1992). As the key factor in this epidemic, the abnormal drought changed to condition of natural steep gradient streams, making it a suitable environment for mosquito larval development, increasing the vector population, to sustaining malaria population within the vector and also constant transmission to human population. As result of malaria emergence, there was dramatic increase in malaria infection, where about 36 cases of clinical diagnosis were reported in the Jayawijaya district between August and October 1997 in contrast of near 0 cases in normal years. There were no gender preferences with each gender averaging around 18 per month. Minor differences occurred in all age groups over 10 years. Mortality from malaria was lowest between ages 5 and 9, while those between 0 and 4 was as high as those over 10 years. Shortly after the outbreak, blood slides showed 75% of the cases were caused by P. falciparum that are predominant in lowland regions. This common occurrence with lowland regions resulted from malaria transfer from the lowland to highland regions. Less than 1% of population had mixed infections of P. falciparum combined with P.ovale or P.malariae; and is caused by the relative high success of P. falciparum in comparison with other forms as well as high prevalence of P. falciparumin lowland regions, where the emergence originated. After significant reproduction in red blood cells during the peak of outbreak in October, amount of people carrying gametocytes were high, accumulating to about 25% to 49% of infected individuals, providing high potential to infect mosquitoes in the region that continued the outbreak through November. These values also indicate that a large group of cases were symptomatic, and remained silent throughout the outbreak. The sudden increase in death during the middle of the course of the outbreak indicated that most of the infected population was infected in the beginning of the outbreak period, causing the disease to progress to a stage unmanageable by the body for a large group of people at the same time that eventually terminated their lives within the same week at the height of outbreak. Incidences of malaria declined significantly in December. This is caused by the drying of the transitory pool after months of drought that decreased vector population. Enlarged spleen also found in many village inhabitants. In this incident, changes to natural environment, the rise in temperature together with the drought, gave rise to an emergence of malaria. The temperature rise provided ripe condition for the parasite to develop and be transferred to human populations. The drought, on the other hand, offset other changes in the natural environment, the steep gradient streams, to cause substantial rise in mosquito population, resulting in malaria epidemic. In effect, local villages experienced the malaria emergence as a result of changes in local climate. Evidently, the natural interaction between the abnormal drought and stream beds was an important cause in the emergence of malaria. III. Massive Deforestation and Emergence of Malaria Between 1985 and 1995, human development and population explosions led to deforestation at the rate of 4,257 hectares per year. Massive deforestation along the contours of a 95-km partially paved road between Amazon port cities of Iquitos and Nauta and in the Amazon rainforest drastically altered the abundance and distribution of faunal and floral species In some areas malaria occurrences increased rapidly, and gradual and stable low-level transmission characterized by lower malaria infection rates occurred due to variable ecological transformations caused by forest clearance and human-driven ecological changes after 6 to 8 years of unstable human migration (Castro et al., 2006). Anopheles darlingi is an efficient malaria vector. After elimination of the species in 1968, it reappeared. Tadei et al. (1998) found populations of Anopheles darlingi in 13 of the 14 altered areas in the Brazilian Amazon between 1993 and 1996. In 1995, the species became the most abundant found in settlements near the Amazon forests because it preferred regions of sunlight. Massive forest removal that decreased the amount of canopy, producing suitable regions for the species to inhabit and populate. Larval studies show that while the species do not breed in forest, it has a preference of breeding in grass and crop land, and near shrubs. Deforestation increased grassland and shrubs, and thus increased breeding, resulting in greater vector population. This population increase significantly elevated malaria infection in its population. Deforestation alters soil and vegetations that changes type and amount of animals inhabiting the region, resulting in major changes to the ecosystem. Due to increase soil pH by deforestation that lead to pH increase in river water, more rivers are capable of supporting larval development. The partial shade around forest fringe and river edges and standing water with high pH (Castro et al., 2006) created by changes to ecosystem are components important for larval development, increasing vector population. (Castro et al., 2006) Through attracting the vector to a new habitat, and providing conditions for larval development, deforestation caused malaria emergence. Higher vector population increased amount of vectors with malaria. This increased malaria infection in human populations, causing the emergence. Constant transfer of malaria from humans to mosquitoes help to maintain a stable population of infected mosquitoes that in turn maintains a constant infected human population that is primary of malaria infection among Anopheles of minor carriers of malaria. Malaria is transferred between humans and mosquitoes and mosquitoes and monkeys. The infected monkey and human population function as main reservoir hosts, maintaining malaria presence. As result of emergence of the vector, between 1971 and 1986, P. falciparum increased by 76% transmitted by A. darlingi in Brazil region of Amazon basin was also caused by deforestation. These cases further confirm the links between a significant occurrence of malaria and a large-scale deforestation [65, 66] (Patza et al., 2000). As Coura et al. (2006) shows, 20.4% to 49.5% of individuals with asymptomatic malaria also carries Plasmodium that causes 25% of asymptotic malaria cases in the Amazon region of Brazil (Coura et al., 2006). In Peruvian Amazon, a section of the Amazon basin, malaria incidence increased from 0.4 per 1,000 population and 1.7 per 1,000 per 1,000 population for P. falciparum and P.vivax, respectively in early 1990s. This value rose to and rose to 343 per 1,000 cases of malaria in 1997 with P. falciparum attributes to 45%.(VITTOR et al., 2006) Malaria emerged through past few decades (Alves et al., 2005) Transferred by A. darlingi and P. brasilianum, P. malariae, P. falciparum and P. vivax are present. P. brasilianum, P. malariae are most abundant, P. falciparum and P. vivax with similar quantity occur in lower proportions. As An. darlingi is the primary vector, An. albitarsis, An. aquasalis, An. braziliensis, and An. Strode are minor vectors, and are found infected with malaria occasionally after a outbreak (23) Anopheles darlingi is the most efficient vector for malaria in the region , and is attributed to several features: 1) it carries more malaria sporozoites more than other Anopheles2) it prefer to feed on humans 3) it occupies large geographic range. 4) it is highly anthropophilic. As the primary vector, it maintains stabilized malaria occurrence in the region.(27) In effect, it is capable of sustaining malaria endemics at very low densities. (28) The mosquito larvae are abundantly found in rivers with relatively high pH. The density of Anopheles darlingi increases from January and peaks in June, with about 16 mosquitoes per person per hour (MPH), before steadily decreases and reaches minimum in December, with about 3 MPH. Human cases changes along this pattern, where the peak amount of cases is about 2600 cases and 500 cases at the minimum point. With about a month in lag between changes in mosquito density and human cases. The chances of a mosquito to be infected increases with blood meal, causing more malaria transfer, to humans, by older mosquitoes populations. (Tadei et al., 1998) The introduction of Anopheles darlingi population to deforested regions of the Amazon basin in effect brought to the area an effective malaria vector that is able to transfer the disease to humans at relatively high rates and to bring about a malaria epidemic in those regions eventually. In reality, the Amazon basin has been experiencing malaria re-emergence since the 1990s, which include the emergence of Plasmodium falciparum malaria, a new species resistant to antimalarial drugs. Thus, in the Amazon basin, as in the Thar Desert and in the highlands of Irian Jaya, major changes made to the natural environment, by massive deforestation, this time, have been attracting new malaria-carrying mosquito species to inhabit and populate as a malaria vector for nearby human populations. Perhaps it is time to recall what Francis Bacon noted a while ago: “We cannot command nature except by obeying her.” Read More