Epidemic Diseases

Of the many diseases spread by insects, none are actually caused by the insects themselves but by other organisms passed on when they feed or bite. Insects are capable of spreading diseases caused by many different types of microorganisms including bacteria, viruses, protozoan and others. Mosquitoes have earned the title of "the most deadly creature on earth." This is due to the fact that they spread serious epidemic diseases such as Malaria, Yellow Fever, African Sleeping Sickness, and West Nile Virus.

Malaria is one of the ten most common, yet deadly diseases in the world. It is a parasitic disease spread by the bite of Anopheles mosquito, which is active between dusk and dawn. Malaria occurs in over 100 countries and territories. More than 40% of the people in the world are at risk. Large areas of Central and South America are considered malaria-risk areas. The World Health Organization estimates that yearly 300-500 million cases of malaria occur and more than 1 million people die of malaria. About 1,200 cases of malaria are diagnosed in the United States each year. Most cases in the United States are in immigrants and travelers returning from malaria-risk areas, mostly from sub-Saharan Africa and the Indian subcontinent.

Persons living in and travelers to, any area of the world where malaria is common may become infected or even in developed countries including the United States. Malaria parasites are transmitted from one person to another by the female anopheline mosquito. The males do not transmit the disease as they feed only on plant juices. There are about 380 species of anopheline mosquito, but only 60 or so are able to transmit the parasite. Humans get malaria from the bite of a malaria-infected mosquito. When a mosquito bites an infected person, it ingests microscopic malaria parasites found in the personЃfs blood. The malaria parasite must grow in the mosquito for a week or more before infection can be passed to another person. If, after a week, the mosquito then bites another person, the parasites go from the mosquitoЃfs mouth into the personЃfs blood. The parasites then travel to the personЃfs liver, enter the liverЃfs cells, grow and multiply. During this time when the parasites are in the liver, the person has not yet felt sick. The parasites leave the liver and enter red blood cells; this may take as little as 8 days or as many as several months. Once inside the red blood cells, the parasites grow and multiply. The red blood cells burst, freeing the parasites to attack other red blood cells. Toxins from the parasite are also released into the blood, making the person feel sick.

For most people, symptoms begin 10 days to 4 weeks after infection, although a person may feel ill as early as 8 days or up to 1 year later. Some parasites can rest in the liver for several months up to 4 years after a person is bitten by an infected mosquito. When these parasites come out of hibernation and begin invading red blood cells, the person will become sick. Malaria is preventable and treatable. Lives can be saved if the disease is detected early and adequately treated. However, the lack of prevention and treatment due to poverty, war, and other economic and social instabilities in endemic areas results in millions of deaths each year.

Yellow fever is a viral tropical disease that is spread to humans by infected mosquitoes. The disease is caused by a virus. Most yellow fever infections are mild. However, the disease can cause severe, life-threatening illness. Yellow fever is found only in parts of Africa and South America. Yellow fever has caused large epidemics in Africa and Northern and Southern America.

There are two kinds of yellow fever: jungle yellow fever and urban yellow fever. Jungle yellow fever usually occurs in monkeys. It is spread from infected monkeys to humans by the bite of an infected female mosquito. Jungle yellow fever is rare and usually occurs in individuals who work in tropical rain forests. Urban yellow fever is a disease that usually occurs in humans. It is spread by the bite of an infected female mosquito that has infected other people. This type of mosquito that usually carries the yellow fever is called Aedes aegypti. Among the two kinds, urban yellow fever is the cause of most yellow fever outbreaks.

The symptoms of yellow fever are varied. The virus has an incubation period of three to six days. The first symptoms will be fever, muscle pain, backache, headache, shivers, and loss of appetite, nausea, and vomiting. Frequently a slow pulse accompanies the fever. Most people improve after three to four days, however in 15% of the cases; patients go into a toxic phase within 24 hours. Fever reappears, and they exhibit jaundice and abdominal pain with vomiting. Bleeding occurs from the mouth, eyes, nose and stomach. The kidneys fail to produce urine, and blood appears in the vomit and feces. Half of the patients who experience this toxic phase die in ten to fourteen days. Due to the fact that many of these symptoms are identical to malaria and other diseases native to the areas, yellow fever is difficult to recognize. Blood tests can identify the virus, but may not be easily available to people in poorer developing countries.

A vaccine for yellow fever is available, and highly effective. The immunity can take effect within one week after vaccination, and protects a person for between ten years and possible for life. The World Health Organization is trying to convince countries in infected areas to incorporate the yellow fever vaccine into their national immunization programs. Travelers and tourists are warned to be vaccinated against this dreaded disease before traveling to countries where yellow fever is present.

Yellow fever cases are increasing, as indicated from records kept over the past 20 years, due in part to changes in the world's environment. This is a result of deforestation, urbanization, and a large unvaccinated population world-wide. Suggested prevention methods include spraying to kill adult mosquitoes, clean up breeding sites, global immunization campaigns, and further research.

African sleeping sickness, also known as African trypanosomiasis is a serious parasitic disease that leads to severe infection of the central nervous system. Parasites of the genus Trypanosoma cause the disease in humans as well as in cattle. If left untreated, the disease is fatal in humans. It is transmitted to humans through the bite of an infected tsetse fly, a grey-brown insect the size of a honey bee. There are two types of the disease, named for the areas of Africa in which they are found. West African trypanosomiasis, which causes a chronic infection lasting years, is caused by the parasite Trypanosoma

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