Several factors affect the transmission of malaria and/or Plasmodium infection in human population. Environmental factors greatly enhances the spread and transmission of malaria because these climatic factors which are more prone in one part of the world than the other helps the female Anopheles mosquito (that harbours the Plasmodium parasite) to thrive and multiply successfully. The spread of malaria infection in a given population is controlled and affected by certain physical and biological environmental factors. These factors either help to increase or reduce the spread and transmission of the disease. These environmental factors which aid or abate the spread and transmission of malaria parasitaemia in a population include climatic factors such as vegetation, rainfall, temperature, and humidity; and biological factors which affect the spread of the parasite.
- Climatic factors: Climatic factors are physical environmental factors that influence the spread and transmission of malaria, and they include vegetation, rainfall, humidity, and temperature. The climate of an area is the average condition of that place over a long time period. The climate of a given geographical area plays significant role in the spread and transmission of malaria. The climatic conditions of a geographical area are always taken into consideration in the epidemiological study of malaria parasitaemia. It gives a clue to the researchers as to why the disease is increasing or abating. Malaria is usually a disease of the tropic and subtropical regions of the world, where the climatic condition is characterized by warmth or hotness. These regions are usually adorned with two seasons which are the dry (harmattan) and wet (rainy) seasons. In other parts of the world (i.e. in the temperate zones), for example, the Antarctic, polar and arctic zones; the weather condition is usually cold and is characterized by four different seasons including: winter, autumn, summer and spring.
- Vegetation: Vegetation is the sum total of plant species (or fauna) found in a particular area at any given time. The distribution of vegetation in a particular area plays key role in the spread and transmission of malaria. The mosquito that transmits the malaria parasites thrives more in areas with high vegetation because such places serve as hideouts for them to lay their eggs and escape possible destruction from humans. Malaria is prominent in swampy and rainforest areas than in the deserts or savanna because swampy and rainforest areas provide stagnant water and vegetation that supports the life cycle of the mosquitoes. It is noteworthy that mosquito lay their eggs in stagnant water which are common in swampy and rainforest areas. But in the deserts and savanna, which are usually dry, there will be no hideouts for the mosquitoes or stagnant water for them to lay their eggs. Thus, arid areas such as deserts and savanna experience low rates of malaria infection while the rainforests and swampy areas are burdened with high rates of malaria disease due to the relatively high amount of vegetation (including trees) that characterize such habitats. Phytoplanktons are aquatic plants which serve as source of food to the larva of mosquitoes. Some vegetation produces nectar (a sugary substance) which serves as food to male Anopheles Clearing of vegetation around residential areas can help to reduce the number of mosquitoes in those areas. The removal of trees, grasses, shrubs and other vegetations around residential areas also influences the spread and transmission of malaria since this practice help to eliminate breeding and resting sites of the insect vector that transmits the parasite which causes the diseases.
- Rainfall: Rainfall is the amount of water that falls in droplets from condensed vapour in the atmosphere. The degree of rainfall coupled with the amount of water in a given area is significant to the rate of spread and transmission of malaria parasites in that geographical location. The insect vector (female Anopheles mosquito) that transmits Plasmodium parasite which causes malaria in humans lays its eggs in water bodies, and this can only be successful in areas that experience high rate of rainfall at any given time. Therefore, there are lesser insect vectors for malaria parasites in the arid zones than in the swampy and rainforests zones where high amount of rainfall provides the required water bodies necessary to flourish the mosquito life cycle. There is massive malaria infection in areas that experience high amount of rainfall compared to desert areas where rainfall is usually very low. Emptying containers that store water and draining of drainages can help to reduce the number of mosquitoes that transmit Plasmodium parasites, because the insect vectors will not find a place to lay their eggs.
- Temperature: Temperature is the degree of hotness or coldness of a particular environment at any given time. In temperate zones, where the temperature is usually low, there is freezing of water bodies, and this makes it difficult for the mosquito larva and pupa to thrive. Such cold regions make it difficult for adult mosquitoes to be active, and this accounts for the low infestation and low malaria parasitaemia in these zones. Warm and hot regions of the world (tropics and subtropics) are good breeding grounds or habitat for mosquitoes. The water bodies in these zones do not freeze as is the case in temperate zones, and this allows the larva and pupa of the mosquito to survive and produce the adult mosquito which transmits and spread the Plasmodium The warm environment in the tropic and subtropical zones also allow the mosquito to be active in its breeding and blood sucking activities. High temperatures also favour the development of the different stages of the Plasmodium parasite within the female Anopheles mosquito.
- Humidity: Humidity is the wetness of the atmosphere of a place at any given time. It increases following increased amount of rainfall in a given geographical area. Humidity also play key role in the spread and transmission of malaria disease in a given geographical zone. Blood sucking female Anopheles mosquitoes are more active in high humidity areas than in relatively low humidity zones. High humidity which creates moist and wet environments also favours the development of the malaria parasite within the body of the insect vector, and also it increases the number of blood sucking mosquitoes in a given area since conditions allows adult mosquitoes to undergo fertilization and lay their eggs.
- Biological factors: Biological factors are other factors aside physical (climatic) factors that influence the spread and transmission of malaria disease within a given geographical Some of the biological factors that affect malaria transmission include:
- Food availability for the insect vector.
- Large production of eggs by the insect vector.
- Availability of long limbs which allows them to settle on the body of human host and suck blood almost unnoticed.
- Building of damns and lakes which provide stagnant water for insect vector to thrive in their breeding activities.
- Agricultural activities of man such as building of fish ponds and irrigation which provides stagnant water that allows the insect vector to lay their eggs and continue their life cycle.
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