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Malaria, Its Causes and Symptoms

What is Malaria What is Malaria

Malaria is one of the most common infectious diseases and an enormous public health problem. Malaria is one of the leading causes of disease and death in the world. It is estimated that there are 300-500 million new cases every year, with 1.5 to 2.7 million deaths worldwide. Malaria is an infectious disease characterized by cycles of chills, fever, and pain and sweating. Historical records suggest malaria has infected humans since the beginning of mankind.

For thousands of years malaria has been a deadly scourge, and it remains one today. From American president John Adams who nearly succumbed to malaria in Amsterdam while on a diplomatic mission, back down the timeline to the early Chinese, Indians, Greeks, and Romans, malaria has not spared its victims, rich or poor. It wasn’t until the 19th century that information about the true cause of malaria became known. Yet despite this knowledge, malaria still ravages Sub-Saharan Africa, South-East Asia and Latin America, taking as its victims mainly young children and pregnant women.

The name "mal" "aria" (meaning "bad air" in Italian) was first used in English in 1740 by H. Walpole when describing the disease. The term was shortened to "malaria" in the 20th century. C. Laveran in 1880 was the first to identify the parasites in human blood. In 1889, R. Ross discovered that mosquitoes transmitted malaria.

There are four species of Malaria. Of the four species of malaria, the most serious type is Plasmodium falciparum malaria. It can be life-threatening. The other three species of malaria (P. vivax, P. malariae, and P. ovale) are generally less serious and are not life-threatening Although malaria has been virtually eradicated in countries with temperate climates, it's still prevalent in tropical and subtropical countries in Africa, Asia, the Middle East, South America and Central America. Evolving strains of drug-resistant parasites and insecticide-resistant mosquitoes continue to make this disease a global health issue. Malaria remains one of the world's leading infectious killers, particularly of children in sub-Saharan Africa. Most American cases of malaria develop in travelers who have recently returned from parts of the world where malaria is widespread. Generally, Africa carries the highest risk for the most serious cases.

Parasitic Plasmodium species also infect birds, reptiles, monkeys, chimpanzees and rodents. There have been documented human infections with several simian species of malaria, namely P. knowlesi, P. inui, P. cynomolgi, P. simiovale, P. brazilianum, P. schwetzi and P. simium; however, with the exception of P. knowlesi, these are mostly of limited public health importance. Although avian malaria can kill chickens and turkeys, this disease does not cause serious economic losses to poultry farmers. However, since being accidentally introduced by humans it has decimated the endemic birds of Hawaii, which evolved in its absence and lack any resistance to it.

Causes of Malaria Causes of Malaria

Malaria is caused by protozoan parasites of the genus Plasmodium (phylum Apicomplexa). This group of human-pathogenic Plasmodium species is usually referred to as malaria parasites.Plasmodium enters the bloodstream and destroys red blood cells and affects the liver, kidneys, spleen and other organs. Other names for malaria include Quartan malaria; Falciparum malaria;Biduoterian fever;blackwater fever;Tertian malaria; and Plasmodium. Malaria parasites are transmitted by female Anopheles mosquitoes.

Evolving strains of drug-resistant parasites and insecticide-resistant mosquitoes continue to make malaria a global health problem. A one-celled parasite, plasmodium, causes malaria. About 170 species of plasmodium exist, but only four cause malaria in humans:  P. falciparum. This species, predominant in Africa, produces the most severe symptoms and is responsible for most malaria deaths.  P. vivax. This species, found mostly in tropical areas of Asia, produces less severe symptoms but can remain in your liver and cause relapses for up to four years.  P. malariae. This species, found in Africa, can cause typical malaria symptoms, but on rare occasions it can remain in your bloodstream for years without producing symptoms. In these cases, you may pass on the parasite to a mosquito or to another person through a blood transfusion.  P. ovale. This species is found mostly in West Africa. Although rare, it can also remain in your liver and cause relapses for up to four years.

The Process of Transmission

The parasite's primary (definitive) hosts and transmission vectors are female mosquitoes of the Anopheles genus. Young mosquitoes first ingest the malaria parasite by feeding on an infected human carrier and the infected Anopheles mosquitoes carry Plasmodium sporozoites in their salivary glands. A mosquito becomes infected when it takes a blood meal from an infected human. Once ingested, the parasite gametocytes taken up in the blood will further differentiate into male or female gametes and then fuse in the mosquito gut. This produces an ookinete that penetrates the gut lining and produces an oocyst in the gut wall. When the oocyst ruptures, it releases sporozoites that migrate through the mosquito's body to the salivary glands, where they are then ready to infect a new human host. This type of transmission is occasionally referred to as anterior station transfer. The sporozoites are injected into the skin, alongside saliva, when the mosquito takes a subsequent blood meal. Only female mosquitoes feed on blood, thus males do not transmit the disease. The females of the Anopheles genus of mosquito prefer to feed at night. They usually start searching for a meal at dusk, and will continue throughout the night until taking a meal.

Normally, 10 to 15 days go by between being infected and the onset of the disease, but it may be longer if the patient has taken a preventive medicine. On a purely practical level, the most malignant (P. falciparum) cases develop within three months of leaving the malaria region, while the forms transmitted by P. vivax and P. ovale may not appear until three years later. Malaria malariae (a rare, benign form) can survive in man for up to 30 years, luckily without causing much discomfort. This form can also be treated, provided you get the right medication. The actual attacks of malaria develop when the red blood corpuscles burst, releasing a mass of parasites into the blood. The attacks do not begin until a sufficient number of blood corpuscles have been infected with parasites.

Other Means of Transmission

A pregnant woman can transmit the infection to her unborn baby. Malaria also can be transmitted through blood transfusions. In the United States, steps have been taken to prevent this type of transmission. People who have been in a malaria-endemic area are prohibited from donating blood for a year after returning from such an area, or three years if they've been a resident of a malaria-endemic area or have been treated for malaria.

The Symptoms

The parasites multiply within red blood cells, causing symptoms that include symptoms of anemia (light headedness, shortness of breath, tachycardia etc.), as well as other general symptoms such as fever, chills, nausea, flu-like illness. There may be a feeling of tingling in the skin, particularly with malaria caused by P. falciparum. People with severe P. falciparum malaria can develop bleeding problems, shock, liver or kidney failure, central nervous system problems, coma, and can die from the infection or its complications. Cerebral malaria (coma, or altered mental status or seizures) can occur with severe P. falciparum infection. It is lethal if not treated quickly; even with treatment, about 15%-20% die. The classical symptom of malaria is cyclical occurrence of sudden coldness followed by rigor and then fever and sweating lasting four to six hours, occurring every two days in P. vivax and P. ovale infections, while every three for P. malariae. P. falciparum can have recurrent fever every 36-48 hours or a less pronounced and almost continuous fever. For reasons that are poorly understood, but which may be related to high intracranial pressure, children with malaria frequently exhibit abnormal posturing, a sign indicating severe brain damage.

Malaria has been found to cause cognitive impairments, especially in children. It causes widespread anemia during a period of rapid brain development and also direct brain damage. This neurologic damage results from cerebral malaria to which children are more vulnerable. Severe malaria is almost exclusively caused by P. falciparum infection and usually arises 6-14 days after infection. Consequences of severe malaria include coma and death if untreated—young children and pregnant women are especially vulnerable. Splenomegaly (enlarged spleen), severe headache, cerebral ischemia, hepatomegaly (enlarged liver), hypoglycemia, and hemoglobinuria with renal failure may occur.

Renal failure may cause blackwater fever, where hemoglobin from lysed red blood cells leaks into the urine. Severe malaria can progress extremely rapidly and cause death within hours or days. In the most severe cases of the disease fatality rates can exceed 20%, even with intensive care and treatment. In endemic areas, treatment is often less satisfactory and the overall fatality rate for all cases of malaria can be as high as one in ten. Over the longer term, developmental impairments have been documented in children who have suffered episodes of severe malaria.

Chronic malaria is seen in both P. vivax and P. ovale, but not in P. falciparum. Here, the disease can relapse months or years after exposure, due to the presence of latent parasites in the liver. Describing a case of malaria as cured by observing the disappearance of parasites from the bloodstream can therefore be deceptive. The longest incubation period reported for a P. vivax infection is 30 years. Approximately one in five of P. vivax malaria cases in temperate areas involve overwintering by hypnozoites(i.e., relapses begin the year after the mosquito bite).


 

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