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:
- A person is bitten by an nfected mosquito.
- The parasite is carried by the bloodstream to the liver, where
it starts reproducing rapidly.
- 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.
- 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.
- 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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
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Article written by Andrew Heenan BA (Hons), RGN, RMN
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