Malaria is caused by the protozoan parasite Plasmodium. Human malaria is caused by four different species of Plasmodium: P. falciparum, P. malariae, P. ovale and P. vivax.
Humans occasionally become infected with Plasmodium species that normally infect animals, such as P. knowlesi. As yet, there are no reports of human-mosquito human transmission of such “zoonotic” forms of malaria.
The malaria parasite is transmitted by female Anopheles mosquitoes, which bites mainly between dusk and dawn. Females of the mosquito genus Anopheles prefer to feed at night. They usually start searching for a meal at dusk, and continue through the night until they succeed. Malaria parasites can also be transmitted by blood transfusion, although this is rare since blood must be screened before transfusing.
Nature of the disease
Malaria is an acute febrile illness with an incubation period of 7 days or longer. Thus, a febrile illness developing less than 1 week after the first possible exposure can be ruled out as not malaria.
The most severe form is caused by P. falciparum.
The signs and symptoms of malaria typically begin 7–25 days following infection, but may occur later in those who have taken antimalarial medications as prevention. Initial manifestations of the disease—common to all malaria species—are similar to flu-like symptoms and can resemble other conditions such as sepsis, gastroenteritis, and viral diseases.
The presentation may include headache, fever, shivering, joint pain, vomiting, hemolytic anemia, jaundice, hemoglobin in the urine, retinal damage, and convulsions.
The classic symptom of malaria is paroxysm—a cyclical occurrence of sudden coldness followed by shivering and then fever and sweating, occurring every two days (in P. vivax and P. ovale infections, and every three days (for P. malariae. P. falciparum infection can cause recurrent fever every 36–48 hours, or a less pronounced and almost continuous fever.
Young children, pregnant women, people who are immunosuppressed and elderly travelers are particularly at risk of severe disease. Malaria, particularly P. falciparum, in non-immune pregnant travelers increases the risk of maternal death, miscarriage, stillbirth and neonatal death.The forms of human malaria caused by other Plasmodium species cause significant morbidity but are rarely life-threatening. P. vivax and P. ovale can remain dormant in the liver. Relapses caused by these persistent liver forms (“hypnozoites”) may appear months, and rarely several years, after exposure. Latent blood infection with P. malariae may be present for many years, but it is very rarely life-threatening
Life cycle
In the indirect cycle of Plasmodium, a mosquito that is the definitive host transmits sporozoites to a vertebrate host such as a human (the secondary host), thus acting as a transmission vector A sporozoite travels through the blood vessels to liver cells where it reproduces asexually (tissue schizogony) producing thousands of merozoites. These infect new red blood cells and initiate a series of asexual multiplication cycles (blood schizogony) that produce 8 to 24 new infective merozoites, at which point the cells burst and the infective cycle begins anew.
Other merozoites develop into immature gametocytes which are the precursors of male and female gametes. When a fertilised mosquito bites an infected person, gametocytes are taken up with the blood and mature in the mosquito gut. The male and female gametocytes fuse and form an ookinite—a fertilised, motile zygote. Ookinetes develop into new sporozoites that migrate to the insect’s salivary glands ready to infect a new vertebrate host. The sporozoites are injected into the skin, in the saliva, when the mosquito takes a subsequent blood meal.
NB-Only female mosquitoes feed on blood; male mosquitoes feed on plant nectar and do not transmit the disease
Recurrent malaria and diagnosis
Microscopy is the most commonly used method. Despite its widespread usage, diagnosis by microscopy suffers from two main drawbacks: many settings (especially rural) are not equipped to perform the test, and the accuracy of the results depends on both the skill of the person examining the blood film and the levels of the parasite in the blood.
Commercially available RDTs are often more accurate than blood films at predicting the presence of malaria parasites, but they are widely variable in diagnostic sensitivity and specificity depending on manufacturer, and are unable to tell how many parasites are present.
However, incorporating RDTs into the diagnosis of malaria can reduce antimalarial prescription. Although RDT does not improve the health outcomes of those infected with malaria, it also does not lead to worse outcomes when compared to presumptive antimalarial treatment.
In regions where laboratory tests are readily available, malaria should be suspected, and tested for, in any unwell person who has been in an area where malaria is endemic. In areas that cannot afford laboratory diagnostic tests, it has become common to use only a history of fever as the indication to treat for malaria—thus the common teaching “fever equals malaria unless proven otherwise”. A drawback of this practice is overdiagnosis of malaria and mismanagement of non-malarial fever, which wastes limited resources, erodes confidence in the health care system, and contributes to drug resistance.] Although polymerase chain reaction-based tests have been developed, they are not widely used in areas where malaria is common as due to their complexity.

Early diagnosis and treatment of malaria reduces disease and prevents deaths. It also contributes to reducing malaria transmission. The best available treatment, particularly for P. falciparum malaria, is artemisinin-based combination therapy (ACT).

Prevention Measures
Prevention of malaria is currently based on three complementary methods: chemoprophylaxis, protection against mosquito bites and mosquito elimination. While several malaria vaccines are under development, none is available yet.

Malaria chemoprophylaxis is only for travelers to malaria endemic countries, which are classified in three groups, to determine which drug is recommended for chemoprophylaxis. The choice of drugs depends on the travel destination, the duration of potential exposure to vectors, parasite resistance pattern, level and seasonality of transmission, age and pregnancy.

Personal Protection Measures Against Mosquito Bites.
Because of the nocturnal feeding habits of most of Anopheles mosquitoes, malaria transmission occurs primarily at night. Protection against mosquito bites include the use of mosquito bed nets (preferably insecticide-treated nets), the wearing of clothes that cover most of the body, and use of insect repellent on exposed skin.
Mosquito Control
Vector control measures depend on vector species, mosquito biology, epidemiological context, cost and acceptability by populations. The main current measures are focused on reduction of the contact between mosquitoes and humans, the destruction of larvae by environmental management and the use of larvicides or mosquito larvae predators, and destruction of adult mosquitoes by indoor residual spraying and insecticide-treated bed nets.

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