why does malaria occur in tropical countries

Where malaria is found depends mainly on climatic factors such as temperature, humidity, and rainfall. Malaria is transmitted in tropical and subtropical areas, where
Anopheles mosquitoes Malaria parasites can complete their in the mosquitoes ( extrinsic incubation period ). Temperature is particularly critical. For example, at temperatures below 20 C (68 F), Plasmodium falciparum (which causes severe malaria) cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted. In many malaria-endemic countries, malaria transmission does not occur in all parts of the country.

Even within tropical and subtropical areas, transmission will not occur In some countries where transmission has been interrupted through successful control/elimination programs. Generally, in warmer regions closer to the equator Malaria is transmitted year-round. The highest transmission is found in Africa South of the Sahara and in parts of Oceania such as Papua New Guinea. In cooler regions, transmission will be less intense and more seasonal. There, P. vivax might be more prevalent because it is more tolerant of lower ambient temperatures. In many temperate areas, such as western Europe and the United States, economic development and public health measures have succeeded in eliminating malaria.

However, most of these areas have Anopheles mosquitoes that can transmit malaria, and reintroduction of the disease is a constant risk. In the United States, CDC is involved in the following activities: Investigations of outbreaks of locally transmitted malaria and of other occurrences (e. g. , transfusion-transmitted malaria) Develop and update guidelines for malaria prevention and treatment. Work with the U. S. Agency for International Development (USAID) in the planning and implementation of the President s Malaria Initiative (PMI), a $3 billion initiative to rapidly increase malaria control interventions in 19 African countries and 6 countries in the Greater Mekong Subregion in Asia.

Conduct research in malaria-endemic countries to improve understanding of best practices for prevention and treatment of malaria. Provide technical assistance to the national malaria control program and local disease prevention and control partners (e. g. , the reproductive health program responsible for maternal health) to strengthen malaria control activities. Work with key Roll Back Malaria (RBM) partners (e. g. , World Health Organization, the United Nations Children s Fund (UNICEF), the World Bank, and the U. S. Agency for International Development) on malaria control programs.

CDC currently has staff posted at UNICEF, the Global Health Group (University of California at San Francisco), the U. S. Agency for International Development, and the World Health Organization, as well as in 21 malaria-endemic countries. Their work spans the spectrum of policy development, program guidance and support, scientific research, and monitoring and evaluation of progress toward RBM and PMI goals.

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