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  • Malkiat Singh Duhra

Malaria




Malaria is a mosquito-borne infectious disease that affects humans and other animals. The disease is widespread in tropical and subtropical regions. This includes much of sub-Saharan Africa, Asia, and Latin America. In 2019 there were 229 million cases of malaria worldwide resulting in an estimated 409,000 deaths. In Africa, it is estimated to result in losses of US Dollars 12 billion a year due to increased healthcare costs, lost ability to work, and adverse effects on tourism. Malaria symptoms usually begin 10 to 15 days after being bitten by an infected mosquito. If not properly treated, people may have recurrences of the disease month later. In those who have recently survived an infection, reinfection usually causes milder symptoms. Malaria is caused by single-celled microorganisms of the plasmodium group. It is spread through bites of infected Anopheles female mosquitoes. The mosquito bite introduces the parasites from the mosquito’s saliva into a person’s blood. The parasites travel to the liver where they mature and reproduce. Five species of plasmodium can infect and be spread by humans. Most deaths are caused by P. falciparum, whereas P. vivacious, P. ovale, and P. malariae generally cause a milder form of malaria.


Malaria is typically diagnosed by the microscope examination of blood using blood films or with antigen-based rapid diagnostic tests. Polymerase chain reaction test to detect the parasite’s DNA is not very common due to its cost. Infected persons show enlarged spleen, fever, low number of platelets in the blood, higher level of bilirubin in the blood, and normal level of white blood cells.


Symptoms

Symptoms of malaria typically begin 8-25 days following infection but may occur later in those who have taken antimalarial medications as prevention. These are 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 ( tertian fever ) in P. vivax and P. ovale infection, and every three days ( quartan fever ) for P. malariae. P. falciparum infection can cause recurrence fever every 36-48 hours, or a less pronounced and almost continuous fever. Severe malaria is usually caused by P. falciparum and symptoms arise 9-30 days after infection. Symptoms including, abnormal posturing, nystagmus, conjugate gaze palsy ( failure of eyes to turn together in the same direction ), opisthotonos, seizures, or coma.


Life cycle

Only female mosquitoes feed on blood; male mosquitoes feed on plant nectar and do not transmit the disease. Female of genus Anopheles prefer to feed at night. They usually start searching for a meal at dusk and continue throughout the night until they succeed. Malaria parasites can also be transmitted by blood transfusions, although this is rare. The female mosquito transmits sporozoite to humans. A sporozoite travels through the blood vessels to liver cells, where it reproduces asexually, producing thousands of merozoites. These infect new red blood cells and initiate a series of asexual multiplication cycles that produce 8-24 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 fertilized 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 ookinete ( a fertilized motile zygote ). Ookinete develops into new sporozoites that migrate to the insect’s salivary glands, ready to infect a new human/vertebrate host. The sporozoites are injected into the skin, in the saliva, when the mosquito takes a subsequent blood meal.


Control of malaria

Methods used to prevent malaria include medication, mosquito elimination of bites. There is no effective vaccine. It may be controlled by using insect repellents, insecticides, and mosquito nets, etc. Doxycycline and atovaquone can be used with the advice of the medical doctor. Community participation and health education strategies promoting awareness of malaria and the importance of control measures have been successfully used to reduce the incidence of malaria.


Anopheles and other species of mosquito go through four stages in their life cycle; egg, larva, pupa, and adult, The first three stages are aquatic and last 7-14 days, depending on the species and the ambient temperature. Female mosquitoes feed on the blood of humans and other animals and males feed on plant nectar.





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