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Making Sense of ... Malaria

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Malaria

What is malaria?

Malaria is a potentially fatal tropical disease. It is caused by a parasite known as Plasmodium, spread through the bite of an infected female mosquito. It remains one of the biggest health hazards, and accounts for about one million deaths each year.

Where is malaria usually found?

Malaria is endemic in all equatorial, and most tropical and sub-tropical nations; efforts to control the disease have had some effect in South America, but the disease remains a major killer in Africa and Asia. There's a list of affected nations and a useful map here.

How common is malaria?

More than 40% of the population of the planet is at risk of malaria, and it remains the biggest killer in most endemic nations. Malaria is virtually unheard of in temperate nations, such as the USA and Europe, except in recent immigarnts, or people who have visited endemic nations.

How is malaria transmitted?

There is a cycle of infection:

  1. A person is bitten by an nfected mosquito.
  2. The parasite is carried by the bloodstream to the liver, where it starts reproducing rapidly.
  3. Parasites attach themselves to red blood cells getting into the blood stream, and further reproduction occurs. Affected red blood cells burst, infecting other blood cells.
  4. This leads to fever and depletes reserves of oxygen-carrying red blood cells. Additionally, damaged and infected red blood cells and accumulate in vital organs such as the brain and kidney.
  5. When a mosquito bites, it collects newly infected blood, and the cycle of infection is perpetuated, placing others at risk.

In some cases, the parasite may lie dormant in the liver, reactivating and causing disease long after the initial infection.

Is there a genetic / familial / hereditary factor?

Changes in blood cells have been noted in many Malaria-prone populations; the effect seems to be to protect people in childhood, when the mortality risk is highest. Diseases such as sickle cell anaemia offer resistance - but at a price; research suggest that both sickle cell, thalassaemia, and other diseases are a response to Malaria.

Can malaria be spread from person-to-person?

No. malaria has a complex life cycle which means it cannot be passed between human beings.

The cycle involves six stages:

  1. A female Anopheles mosquito feeds on a human and injects Malaria parasites in the form of sporozoites into the bloodstream. The sporozoites travel to the liver and invade liver cells.
  2. Over a number of days (this varies with malaria species), the sporozoites grow, divide, and produce tens of thousands of merozoites, per liver cell. Some species remain dormant for in the liver for weeks or months, causing relapses later.
  3. The merozoites re-enter the bloodstream, invading red blood cells, reproducing asexually, releasing newly formed merozoites from the red blood cells repeatedly over a few days. This can lead to illness and complications of malaria that can last for months if untreated.
  4. Some of the merozoite-infected blood cells develop into sexual forms of the parasite, called male and female gametocytes, that continue circulate in the bloodstream. 
  5. When a mosquito bites an infected person, it ingests blood cells, which burst in the mosquito gut, releasing the gametocytes, which develop further into mature sex cells called gametes. Male and female gametes fuse to form diploid zygotes, which develop into actively moving ookinetes that burrow into the mosquito midgut wall and form oocysts. 
  6. Growth and division of each oocyst produces thousands of active haploid forms called sporozoites. After a week or two, the oocyst bursts, releasing sporozoites into the body cavity of the mosquito, eventually reaching the salivary glands. The cycle of human infection re-starts when the mosquito next takes a blood meal, injecting the sporozoites from its salivary glands into the human bloodstream .

This description is an edited form of the description here, which features an illustration.

Who is most at risk from malaria?

In endemic nations, infants and young children are most at risk; a degree of immunity increases over time. Allunprotected visitors to endemic nations are at high risk, having little natural immunity.

What are the symptoms of malaria?

Symptoms include fever and flu-like illness, including shaking chills, headache, muscle aches, and tiredness. Nausea, vomiting, and diarrhea may also occur.

Malaria may cause anemia and jaundice, because of the loss of red blood cells. Symptoms usually appear between 10 and 15 days after the mosquito bite, but this can vary considerably, with reccurence possible after weeks or months.

Untreated, malaria can rapidly become life-threatening by disrupting the blood supply to vital organs. Untreated infection with Plasmodium falciparum may cause kidney failure, seizures, mental confusion, coma, and death.

When is it necessary to contact a doctor?

Treatment should be sought as soon as possible; flu-like symptoms are a warning after unprotected travel in an endemic area.

What are the long term effects of malaria?

malaria is a very debilitating dsease, and it may takes months to recover fully from a mild, quickly treated bout. Delayed treatment may leave residual kidney damage, with possible effects on other organs. Research suggests that children in endemic area who catch Malaria will have a greater risk of cardiovacular disease, as well as late development and possible cognitive effects.

What is the mortality rate for malaria?

Malaria mortality varies considerably by country: from zero in temperate and colder nations, to 132 per 100,000 according to WHO data. As with most infectious diseases, mortality is highest among the very young and very old, plus those weakened by other conditions, or with poor immune systems. Neonates may have some temporary protection, due to acquired maternal immunity.

How is malaria diagnosed?

In most endemic areas, diagnosis is based on clinic symptoms, as it is very reliable, and cheaper than more 'scientific' methods; but microscopy is the most reliable method, and is used outside endemic areas, and where malaria is less common in endemic areas (eg Asia). There are dipstick tests, but these are too expensive to be practical in most of sub-Saharan Africa, and additionally are limited inthere abilty to distinguish the type of Malaria.

Is there a treatment for malaria?

For  over 100 years, the treatment of choice was quinine, administered by mouth. While quinine is still used (it is still effective, and much cheaper than modern substitutes), severe malaria is generally treated with intravenous Artesunate.

Uncomplicated malaria is treated with oral drugs. The most effective strategy for P. falciparum infection recommended by WHO is the use of artemisinins in combination with other antimalarials artemisinin-combination therapy, ACT, in order to avoid the development of drug resistance against artemisinin-based therapies. Severe malaria requires the parenteral administration of antimalarial drugs. Until recently the most used treatment for severe malaria was quinine but artesunate has been shown to be superior to quinine in both children [82] and adults.[83] Treatment of severe malaria also involves supportive measures.

Is there a way to prevent infection?

People living in endemic areas do build up some immunity, but this does not last long after leaving the area. People travelling to endemic areas will not usually have any immunity, so prearation for the risk is essential: follow the ABCD of malaria prevention.

  • Awareness of risk – check the risk where you are travelling
  • Bite avoidance – take simple precautions to avoid mosquito bites.
  • Check – if you will require malaria prevention medication.
  • Diagnosis – seek help immediately, if you have symptoms while abroad, or a full year after your return home.

What medicines will help avoid malaria?

There are several medicines that can help to prevent malaria, and your doctor's recomendation will be based on your destination, what you expect to be doing, and the duration of your trip.

None of these medicines are totally effective, but you can reduce your risk.

  • Chloroquine - Only given where the risk of developing malaria is low, due to resistance problems, though may be given as well as other medicines. Side-effects include sickness, diarrhoea and headache.
  • Proguanil - usually only given with other medicines, due to resistance problems. Side-effects include diarrhoea or constipation and mouth ulcers.
  • Mefloquine - often used where malaria is resistant to chloroquine. Mefloquine is taken weekly and should be started one to two weeks before travelling. Side-effects include sickness and diarrhoea, headache, dizziness and disturbed sleep.
  • Doxycycline - mostly given to people who cannot take mefloquine. Side-effects include diarrhoea, thrush and heartburn.
  • Proguanil with atovaquone - may be given instead of instead of mefloquine or doxycycline. Side-effects include headaches, sickness and diarrhoea.

The choice of medicine will also be influenced by other factors, including your health and other medicines you may be taking.

Malaria is now resistant to chloroquine in many countries, so either doxycycline, proguanil with atovaquone or mefloquine are usually prescribed for malaria prophylaxis.

Can malaria be controlled environmentally?

  many approaches have been tried, and many more are being tested, but no measures have had proven success except DDT (dichlorodiphenyltrichloroethane), a synthetic insecticide. However, DDT is also proven to be highly damaging to the environment, and overusage can have catastrophic consequences in the fragile soils of endemic malaria areas; additionally, the benefits are transient ( a matter of weeks), while the damage is long term. And there is evidence of increasing malaria resistance to it. While DDT is used, with success, in South Africa (under WHO guidance), there is widespread opposition to it's wider use, despite determined campaigns by industrial interests to drop the restrictions on its use.

What can be learned from history?

Malaria was eleiminated from the USA by 1951, primarily by DDT application to rural homes or  where malaria was prevalent. Almost 5m house spray applications were made. The programme also included drainage, removal of mosquito breeding sites, and spraying (occasionally from aircrafts) of insecticides. But this approach is simply impractical in most endemic areas, where the prevalence is much greater, and poverty is a real issue. Temproary elimination has been achieved in many areas, but the expense of maintaining DDT application (repetition required after a short while), plus the disbenefits of DDT, brough recognition of the futility of this approach on a global level.

Many other intiative have been tried, with variable success - but no total success. The 2011 WHO World Malaria Report, cites 28 countries as having eliminated malaria; but this does not include any of the most endemic areas.

In 2007 the Gates Foundatin committed funds and effort into eradication, and a new taget of global eradication by 2015 has been set. It will not be achieved.

History demonstrates emphatically that Malaria cannot be eradicated globally with the methods currently in use; At the time of writing, no radical new ideas have been offered, and it would be a mistake to have any confidence a quick victory. But science never stands still, and the quest continues to attract many millions of dollars; there is still hope for the longer term.

Bibliography and Further Information Sources

If your question has not been answered, email me at the address below, and I'll try to get the information you seek.

If this article hasn't answered your question, email me at the address below, and I'll try to get the information you seek. I regret I cannot assist with individual cases or essays and school projects, but if it's something I've missed, I'll be happy to try and help.

Article written by Andrew Heenan BA (Hons), RGN, RMN

First Published: 20 February 2012
Last updated: 20 February 2012
© Andrew Heenan 2012
 

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