Trace the historical development of our understanding of the cause and prevention of malaria (make sure you tell us lots about the disease).

MALARIA


Malaria is caused by tiny parasites that is carried from person to person by the female anophes. The saliva of the female mosquito is used to stop blood from clotting and is injected by the mosquito once she pierces the skin. The parasites present in the saliva get injected to the bloodstream, invade the red blood cells, where they divide and multiply mainly in the liver, causing the cell to burst open releasing many more parasites to further infect more cells. If the female mosquito bites an infected person, it absorbs the infected blood and hence becomes a vector, or carrier of the disease.

History
1880 - discovery of the malaria parasite

IIt was originally believed that malaria was caused by living near swampy areas, but Charles Louis Alphonse Laveran, a French army doctor working in Algiers, discovered the protozoan Plasmodium that caused the disease. After examining blood from 192 other malaria patients, he identified the same crescents in 148 of the samples. Later he recognized the four distinct forms in human blood that would prove to be the malaria parasite in different stages of its life cycle. Laveran received the Nobel Prize in 1907 for his discovery of the single-celled protozoan that causes malaria.
1897 - discovery that mosquitoes transmit malaria
On 20 August 1897, Ronald Ross, a British officer in the Indian Medical Service was the first to demonstrate that malaria parasites could be transmitted from infected patients to mosquitoes. He found cysts in the stomach walls of the mosquito Anopheles and identified the cysts as the malaria causing parasited. He also demonstrated in his investigations of bird malaria that mosquitoes could transmit malaria parasites from bird to bird. Ross was awarded the Nobel Prize for his discovery in 1902.
1898-1899 - discovery of the transmission of human malaria parasites
A group of Italian scientists (G. Grassi, A. Bignami, G. Bastianelli, A. Dionisi, A. Celli) confirmed that human malaria parasites pass through the same developmental stages in the mosquito as the bird parasites observed by Ross.
1948 - discovery of the malaria parasite in human tissue
It wasn’t until the 20th century that the third piece of the human malaria puzzle was solved. The question of where sporozoites inoculated by mosquitoes undergo early development in the human host was only answered in 1948 by researchers at the Ross Institute of the London School of Hygiene and Tropical Medicine. They detected malaria parasites in the livers of rhesus monkeys infected with the primate malaria species.

Symptoms

Symptoms will usually appear 10-15 days after being bitten but depending on the plasmodium it can range between 9 days and 30 days. Some strains of the Plasmodium vivas might take up to nine months before they start showing symptoms.
  • The first signs is a sudden break out in a fever
  • headaches
  • aches and pains all over
  • diarrhea
  • shaking chills
  • sweating
  • abdominal pains
left untreated malaria will leave you weak, groggy and with yellowish skin.
As the parasites increasingly clog up your bloodstream, the disease can lead to vomit convulsions, and, finally kidney failure and/or cerebral malaria (in which you fall into a coma in which you never awaken). Either way, both of these conditions will lead to death.

Diagnosing

Malaria is a life threatening illness and should be properly and quickly diagnosed. Often early malaria symptoms can resemble symptoms of other diseases including typhoid and meningitis. It is crucial to have a blood sample, if you do have malaria the parasites will show up, if not right away then soon enough. Although blood is the sample most frequently used to make a diagnosis, both saliva and urine have been investigated as alternative, less invasive specimens. Another way in distinguishing malaria that has proven to be highly effective is malarial retinopathy. This involves large, prospective autopsy study of children dying with cerebral malaria in Malawi found that malarial retinopathy was better than any other clinical or laboratory feature in distinguishing malarial from non-malarial coma. The detection of malarial retinopathy is a candidate diagnostic test for cerebral malaria. Malarial retinopathy consists of a set of retinal abnormalities that is unique to severe malaria and common in children with cerebral malaria.


Prevention

Methods used to prevent the spread of disease, or to protect individuals in areas where malaria is endemic, include prophylactic drugs, mosquito eradication, and the prevention of mosquito bites. These continues prevention methods have rapidly decreased the existence and prominance of malaria all around the world, in particular regions of world from which malaria has been almost eradicated are North America, Europe and much of the Middle East, although increased extensive travelling and migration is counter-productively increasing instances of malaria around the world.
Methods of preventing malaria include
  • Vector control, which involves destroying mosquito breeding grounds and genetically modifying species of mosquitoes
  • Prophylactic drugs which can be practical for tourists visiting the malaria endemic areas, but not practical for residents of these areas as they have to be taken weekly, or even daily
  • Indoor residual spraying, which involves spraying the walls of residential dwellings with insecticide as mosquitoes generally rest on walls after a blood meal
  • Mosquito nets and bedclothes, Insecticide treated nets can reduce chances of being bitten by upto 78% according to several sources
  • Quinine, an age long treatment for malaria used presently to treat severe and cerebral cases of malaria
  • Vaccines, are not effectively available as the malaria parasites are continually evolving and developing immunity to treatment methods
Commonly malaria has been treated with drugs, however, recently both the parasite and mosquito have begun to develope resistance to the chemicals. The uses of recombinant DNA techniques have been tried to act as effective vaccines, stimulating the immune system to attack the parasite, but because of the course of evolution, parasites have developed ways of altering these protiens, thereby evading attacks by the immune system.

The Plasmodium (Malaria) Lifecycle



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Infected mosquito releases saliva (infected with Plasmodium) into the human
host's bloodstream while having a bloodmeal.

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Sporozoites make their way into the liver via circulatory system.

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The Sporozoite feeds and grows whilst inhabiting liver cells.

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The Sporozoites nuclei divides many times to produce Plasmodium cells in the form of Merozoites.
About a week later, the liver cell bursts and the Merozoites enter the bloodstream.

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Whilst in the bloodstream the Merozoites infect red blood cells and reproduce
and again burst out and repeat the process. This yields a cycle of infection and
eruption. Red blood cells are syncronized with their eruption and this is characterized by fevers, and illness.

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Some Merozoites form into sexual structures called gametocytes, either male or female.
Gametocytes become large oval structures within the red blood cells.

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Gametocytes do not harm the human host, but when taken into the mosquito gut during a
bloodmeal they represent the next stage of the Plasmodium lifecycle.

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In the mosquito's gut the Gametocytes escape from the red blood cells and form
into male and female sex cells called Gametes.

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These two sex cells fuse to create the first cell of the next generation.

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They are called Zygotes. Zygotes mature into motile cells called Ookinetes.

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The Ookinete morgates to the wall of the mosquito's gut where it develops into an Oocyst.

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In the Oocyst, cell division occurs many times, and again creates cells in the form of Sporozoites.

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The Oocyst eventually ruptures and releases the Sporozoites.

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The Sporozoites migrate to the salivary glands.

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From the Salivary Glands the Sporozoites can infect the next human host, thus repeating the Plasmodium lifecycle.


References


Mick Isle (2001) "Epidemics - Deadly Diseases Throughout History - Malaria" Published by The Rosen publishing group, Inc.
Sally Morgan, "Fighting Infectious Disease" Published by
Wikipedia, Malaria http://en.wikipedia.org/wiki/Malaria, accessed on Feb 1, 2010
World Heatlh Organization (2010) "Malaria", Available at http://www.who.int/topics/malaria/en/. Accessed Feb 2, 2010
Malarial Retinopathy,http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2367432/ accessed Feb 2, 2010
Sumanas Inc, "Plasmodium, The Malaria Parasite", Available at http://www.sumanasinc.com/scienceinfocus/sif_malaria.html. Accessed Feb 2, 2010


QUESTIONS:

1. DRAW a timeline showing how our understanding of the cause and prevention of malaria has progressed.

2. CONCTRUCT a simple flow diagram outlining the plasmodium life cycle (you can use your class notes to help with this).