Discuss about the Epidemiology of Communicable Disease for Malaria.
The continued incidence of malaria all over the world in endemic areas continues to be a public health challenge. India is one of the countries where the scourge of the disease has been difficult to control owing to the tropical and sub-tropical ecology that favours the growth of the mosquito vector. The global incidence of malaria in Southeast Asia, Africa and South America has also been high. The control measures that are adopted include vector control through the use of insecticides and other strategies. The parasite control through the use of newer drugs, vaccines and sustained malaria control programs are being used to eliminate the disease.
Epidemiology of malaria in India
Malaria is a major public health problem in 104 countries, causing illness in 207 million people causing 627,000 deaths annually. India accounts for 70-80% of the cases of malaria in South Asia and about 1000 deaths occur due to malaria every year in the country that is known for tropical weather conditions (Dash, Valecha, Anvikar, & Kumar, 2008; Anvikar, et al., 2016). There are reports that the actual number of deaths due to malaria may be 10 to20 times higher than those reported (Manguin, 2013). The occurrence of rain provides the climate for the breeding of the mosquitoes that are the Plasmodium vector. There occurs tremendous heterogeneity in the malaria because several ecotypes of the pathogen exist in different parts of the country. The transmission of the malarial protozoan, Plasmodium, occurs through mosquitoes that belong to the genus Anopheles. The genus has 465 species that have been recognized taxonomically and 50 member species that are yet to be named (Sinka, et al., 2012). The transmission of malaria occurs through six primary vectors, Anopheles culicifacies, Anopheles stephensi, Anopheles dirus, Anopheles fluviatilis, Anopheles minimus and Anopheles epiroticus.
Multiple species of the malaria parasite and the vectors cause the endemicity of malaria in India. Four species of the malaria parasite cause malaria in India. Plasmodium falciparum and Plasmodium vivax are common, while malarial cases due to P. malariae and P. ovale are rare. Historically, the P. vivax has caused the larger number of malaria cases but of late P. falciparum malaria cases are more frequent and have occurred in larger numbers. Some areas have reported simultaneous occurrence of malaria caused by both the species (Das, 2012).
The climatic conditions of rainfall, relative humidity and temperature play a major role in the incidence of malaria. It is recognised as a disease that is among the most sensitive to temperature (Bi, et al., 2013). The fact that large parts of India are tropical and the average temperatures range between 15-30 degree Celsius and rainfall and precipitation occurs across states through the year makes the climate conducive to the breeding of mosquitoes. Most cases of malaria are reported from the Eastern states of Orissa, Jharkhand, Bengal, central states of Madhya Pradesh and Chhattisgarh and the Western states of Gujarat, Rajasthan and Karnataka (Das, 2012). Environmental change due to changes in climate and manmade ecological changes, such as, construction of dams, intense agriculture, rapid urbanisation and deforestation contribute to a shift from rural malaria to urban malaria, industrial to travel malaria and forest to plain malaria in the Indian context (Das, 2012).
Global epidemiology and ecology of malaria
Apart from India, malaria is endemic to several regions around the world in Southeast Asia, East Africa and South America. In the current context the global ecology has become altered due to human intervention and climate change has affected the way malaria is expected to spread due to the impact of green house gases and land use. The malaria parasite circulates from the reservoir host, the Anopheles mosquito to humans and causes disease (Kaewwaen & Bhumiratana, 2015). The feeding activity and ability of the vectors to breed in a shaded habitat can cause increase in malaria incidence. Anthropogenic changes in land use change may alter the risk of transmission of malaria and thus render human beings susceptible to malaria.
Transmission in rural areas is considered to be higher than in urban areas. The night time bite by a female Anopheles mosquito when in an unprotected environment causes an infection among humans. Those working in agricultural fields are more vulnerable to transmission of malaria due to stagnation of irrigation water. In a study that compared malaria transmission at three locations in Brazil, Chennai and Panaji city in Goa, India, Columbia, Malawi, Senegal and Uganda, it was found that a high degree of annual rainfall and a conducive temperature caused transmission of malaria. Maturation of the vector to adult stage and transmission to humans usually begins after the seasonal rainfall begins. In urban areas risk of transmission is higher people who live in the vicinity of small urban parks, water storage tanks (Wilson, 2015). The incidence of malaria in urban environments has seen a decline due to improved dwellings, drainage of water which could become a breeding place of the vectors. better personal protection, houses that are mosquito proof and improved diagnosis and treatment have caused a decline in the incidence of malaria in urban areas (Wilson, 2015). In Africa, the incidence of malaria has remained high due to conditions of climate and temperature that are optimal for the breeding of mosquitoes. Several efforts at reducing the disease burden have been made but incidence, morbidity and mortality remain high (Snow, 2015).
In India, the National Malaria Control Program in 1953 was based on the use of the insecticide DDT to kill the vectors and medication when required. Malathion was used from 1960s to control the vector population. Due to the development of insecticide resistance the insecticides used are not effective against all vector species. Later the program was modified and low incidence of malaria was achieved. But a resurgence of the disease occurred in the early 1970s. The current program to eradicate malaria was launched in 2016 and it is called the National framework for malaria eradication from 2016-2030. Strategies to control malaria include, vector control and parasite control. Medicines are dispensed through dispensaries and hospitals. Vector control has to be done through a multi pronged approach that includes reduction at source, use of larvicides, use of larvivorous fish, use of space spraying and environmental management and modification. This approach is for reducing the incidence of malaria in urban areas. Low quality housing and crowded living in slums is the main reason for increased breeding of mosquitoes and transmission of malaria (Searo.who.int).
The use of chloroquin was the main arsenal in treating a Plasmodium infection. But the use of artemisinin derivatives has helped malaria that is resistant to chloroquin. The recent emergence of strains resistant to artemisinin is a cause for serious concern. Drug resistant malaria will be difficult to treat and in several countries the lack of resources has made it difficult to identify cases of drug resistance.
Work on the development of a malaria vaccine is in advanced stages and some versions have been released. A pilot program was launched in Ghana, Malawi and Kenya for vaccination of children from April 2017. The incidence of malaria in the pilot study was reduced to 31% among children. The name of the vaccine is RTS, S and is being used in Africa (WHO).
Prevention of malaria through the use of insecticide treated mosquito nets and spraying residences with insecticides has yielded improvement and the number of cases have declined considerably. A 37% decline in the cases of malaria and a 60% fall in the number of deaths has achieved, globally. While many countries have been able to eradicate malaria completely, others have achieved low incidence and have embarked upon programs for complete elimination (Shretta, Avanceña, & Hatefi, 2015). Previous experience has shown that resource crunch has been the main reason for the weakening of control measures employed and this has led to resurgence of malaria. Consistent economic inputs and maintenance of funding is vital to achieving elimination of malaria. Minor reasons such as travel or "airport malaria" can transmit the infection that are epidemiologically vulnerable and entomologically receptive (Huang & Tatem, 2013).
The epidemiology and ecology of malaria are well understood. The incidence of malaria continues and the cases of resurgence time and again means that the efforts have to be sustained through better funding. The temperature and intermittent rainfall and relative humidity contribute to the incidence of malaria. The countries with tropical and sub-tropical climates have the maximum number of cases and fatalities due to malaria. The use of vector control through control of the Anopheles mosquitoes through insecticides, improved drainage of water and other biocontrol measures has helped in the prevention. The development of malaria vaccine shows promise and its efficacy is being tested among children in Africa. The development of drug resistance in Plasmodium has made treatment of malaria difficult. Earlier chloroquin was used for treatment. It has now been replaced by artemisinin but the development of resistance to this new drug has caused considerable concern. Continued funding and sustained efforts can help reduce incidence and help nations succeed in elimination efforts.
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