Are Anti-malaria pills necessary if no mosquito bites?

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QUESTION

We had a weekend in the Kruger Park and all of us took anti malaria pills beforehand. None of us was bitten or even saw a mosquito, do we need to carry on taking them for so long?

ANSWER

Since you say “so long”, I assume you are either taking doxycycline or Lariam, both of which are taken for four weeks after leaving the malarial area. Unless you are experiencing severe side effects, it is always recommended to continue taking prophylactic medication for the full course, the reason being that the malaria parasite has a latent period of up to a few weeks, and the prophylactics only kill the parasite after this latent stage. Even though you didn’t see any mosquitoes, the possibility remains that you got bitten and did not notice – ultimately, you can weigh up the slight inconvenience of taking the pills for a while longer versus the slight risk, but enormous inconvenience of getting malaria!

Since you have taken malaria prophylactics, please take a moment to fill out the Malaria Medication Side-effects Survey: Treatment and Prophylaxis!

Thank you!

Pregnant Women and Malaria

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QUESTION

Why are pregnant women and children at the highest risk of getting malaria?

ANSWER

The reason why pregnant women and children are at greater risk of contracting malaria is due to their reduced levels of immunity. Children living in malarial areas have less immunity than adults because they have had less exposure to malaria, and so their immune systems have not had a chance to develop antibodies to protect against the disease. Pregnant women, although they may normally have good immunity, witness changes in their immune systems during pregnancy in order for the woman to carry the child.

Given that a baby is genetically distinct from its mother, the mother’s immune system has to be modulated in order to ensure that the body’s defenses do not act against the baby, as they would some other foreign object such as an infection. While this immune modulation allows the mother to carry her foetus, it does leave her vulnerable to other infections, such as malaria. In areas of high malaria transmission, the mother may still retain enough immunity to not present with severe symptoms of malaria. In these cases, the dangers of malaria in pregnancy come from resulting anemia in the mother, as well as passage of malaria antigens or the parasite itself through the placenta and to the foetus, which can result in problems for the baby.

Interestingly, a study came out last year which showed evidence that using long-lasting insecticide treated bednets increased malaria prevalence in older children and adults, probably because the nets protected against even sub-clinical exposure to malaria and therefore the levels of natural immunity in people using the nets declined over time, leaving them more susceptible to infection. However, this result has been controversial, as in other studies community-wide coverage of bednets has reduced overall malaria incidence due to reduced transmission.

Post-infection Malaria Medication

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QUESTION

My daughter has recently returned from a trip to Borneo. Even with aggressive preventive anti-mosquito behaviour (long sleeves/pants, deet applications and mosquito netting) but not anti-malarial medication, she received over 30 bites. She is now exhibiting some symptoms (body aches, headache and severe fatigue). She has an appointment at the doctors in 2 days time. Is there some kind of post-trip medication (like doxycycline) she can take as a precaution even if the malarial test comes back negative at this early of a time. Thanks.

ANSWER

The important thing to note here is that if your daughter has symptoms of malaria, then she should be diagnosed and, if positive, treated with medication aimed at curing active malaria. Doxycycline is NOT a drug used for the treatment of malaria, so there is no point taking it if she is already exhibiting symptoms.

Furthermore, some types of malaria found in Borneo (notably P. falciparum and P. knowlesi) can become more severe very quickly – 2 days may be too long to wait. If you live in an area where malaria transmission occurs, you may be able to buy a self-testing kit (also known as a rapid diagnostic test, or RDT) for malaria in a local pharmacy. Otherwise, if your daughter’s symptoms get worse, you should take her to an emergency room and explain her travel history and subsequent risk of having malaria.

There is no substitute for taking prophylactic malaria medicine; it might be that if your daughter had started taking prophylactic medicine as soon as she started receiving multiple mosquito bites, then she may have been protected to some degree. However, malaria has a latent period, and so she would have had to continue taking the medication for a period of time after returning home as well – with doxycycline, this means taking the drug for a further four weeks.

Malaria in Africa

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QUESTION

What is the current problem for malaria in Africa?

ANSWER

Malaria is a particularly severe problem in Africa due to a number of reasons. First of all, transmission in many parts of Africa occurs year round, due to favourable conditions for the development of the mosquitoes malaria requires as its vector.

Secondly, the dominant and most widespread species of malaria in Africa is Plasmodium falciparum, which is most fast-acting and deadly form of the disease.

Thirdly, Africa has a very young population; birth rates are high across much of the continent, and in many countries, more than 40% of the population is under 15 years old. Given that young children are are higher risk of malaria than adults, this also increases the burden of malaria in Africa compared to other parts of the world.

Finally, access to health care and malaria control interventions in Africa has been plagued by more general issues of slow development. While national health systems are slowly emerging, many countries are still reliant on foreign aid and NGOs to provide even basic health services.

Even where these organisations can provide health care, they often face challenges such as reaching remote populations without good road access, finding ways to provide medical services without reliable electricity or communications networks and maintaining supply chains of diagnostic tools and crucial medicine.

However, signs of progress are being seen. Long-lasting insecticide treated bednets have been put forward as a key preventative measure against malaria, and to date millions have been distributed to people living in malarial areas in Africa, and particularly to high risk groups such as young children and pregnant women.

Simultaneously, other control initiatives, such as indoor residual spraying, are gaining traction and being deployed in more areas. An emphasis on local capacity building has encouraged community involvement in drug distribution and access to health care initiatives, as well as training local health workers in diagnostic methods in rural areas.

Encouraging reports from groups such as Malaria No More and the Roll Back Malaria consortium suggest that the number of deaths from malaria in Africa last year was the lowest in history, and efforts are underway to reduce that number to zero, worldwide, by the year 2015.

Malaria Distribution

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QUESTION

What countries have malaria?

ANSWER

Prior to the advent of modern methods for controlling malaria, it was present on every continent in the whole except Antarctica. The transmission of malaria depends on an appropriate climate, both for the development of the parasite and the mosquitoes that it requires as a vector. This limits malaria to areas that are sufficiently warm and with sufficient rainfall to provide pools of stagnant water for the development of mosquito larvae.

In practice, this means that malaria can be transmitted year round in the tropics (apart from areas of high altitude and deserts), most of the year in the sub-tropics (predominantly during rainy periods) and even seasonally in temperate latitudes (during the warmer months). As a result, malaria has historically been present in the United States and even in England, at a latitude of over 50 degrees north.

However, modern control measures, such as insecticide spraying and epidemiological surveillance, has greatly reduced transmission of malaria in many parts of the world, and especially in temperate regions where the force of infection was already lower than elsewhere in the world. As such, nowadays malaria is confined to tropical and sub-tropical Central and South America, certain Caribbean islands (such as Haiti), sub-Saharan Africa (apart from most of Namibia and South Africa), parts of the Middle East, the Indian sub-continent, south-east Asia (excluding major cities such as Singapore) and many of the Indo-Pacific islands (including Papua New Guinea). Of these, by far the largest number of deaths from malaria occur in sub-Saharan Africa.

See the CDC’s interactive map of malaria distribution for more information.

Where did malaria start in Africa?

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QUESTION

Where did malaria start in Africa?

ANSWER

Malaria has been present in Africa for tens of thousands of years; given this ancient history, it is very difficult to know exactly where it first entered the continent. Also, there are several different types of malaria in Africa, which have likely had different histories, and malaria researchers continually unearth new evidence regarding the origins of these different species.

For example, it has long been thought that Plasmodium falciparum, the most deadly form of malaria, emerged somewhere in the western Congo Basin in Central Africa. Originally, it was thought to have crossed over into humans from a closely related species found in chimpanzees, but recent research, published only in 2010, has suggested that a new species, found in gorillas, is actually the closer relative.

Plasmodium vivax, the most geographically widespread species of malaria that infects humans, has less clear origins. Many of its closely related species occur in south-east Asia, which leads some researchers to suggest this is where it emerged, passing into Africa as humans and their livestock moved across Asia towards the Middle East and North Africa, or possibly via  migration through Madagascar. However, other researchers argue that the high prevalence of certain genetic mutations which protect against Plasmodium vivax malaria found in populations in Africa and of African descent, and particularly West Africa, is evidence that P. vivax actually originated on this continent.

How long do I need to carry a Malaria Risk Card

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QUESTION

Hello, 13 months ago I worked in Nigeria, Africa for a period of 6 weeks. During which time I took Malarone tables daily. I think I was only bitten once or twice when there – but have never had Malaria. I currently carry a Malaria Risk Card in my wallet. At the time I was told I could potentially contract Malaria up to a period of 2 years after exposure – is this correct, or can I now remove the Risk Cards from my wallet?

ANSWER

If you never had malaria while you were in Nigeria, then you certainly would not still be at risk from it now. The only case in which you might still be at risk is if you had been diagnosed with either Plasmdodium ovale or P. vivax (two of the five forms of malaria that infect humans) – these can cause relapses months or even years after initial infection.

However, as I said above, since you did not have malaria at all, this does not apply to you. It is true that malaria has a latent phase, and so can sometimes only start to cause symptoms after someone returns home from a malarial area, but this period is usually one or two weeks, and certainly not months or years!

Transmission of Malaria

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QUESTION

Why can the malaria parasite be transmitted from mosquito to human, but not from human to human (via blood)?

ANSWER

This is a very good question, and actually, malaria can be transmitted via human blood directly to another person, but this occurs relatively rarely!

It has to do with the life cycle of the malaria parasite. When a mosquito bites a human host, it injects sporozoites from its salivary glands into the blood. This life stage first migrates to the liver, where it undergoes a cycle of multiplication, before entering the blood stream. Here, in the so-called “erythrocytic” portion of the life cycle, the parasite reproduces a series of times in red blood blood, before finally forming gametocytes, which are required to be ingested by a mosquito vector during another blood meal for the life cycle to be continued. As such, when blood is passed between people, they would have to pass infected red blood cells, and not gametocytes (which are not infective to humans, only to mosquitoes) in order for the other person to become infected.

As such, when a person who is infected with malaria donates blood, there is a chance that they might pass on some red blood cells which are infected with mature trophozoites or schizonts; these could then go on to infect more red blood cells in the person who received the blood. However, in most countries, blood is screened for malaria, and in fact, in many places, people who might have been exposed to malaria are not allowed to donate whole blood, only plasma (in which the red blood cells have been removed, and therefore there is no risk of transmission). Given the high levels of malaria prevalence in some endemic countries, however, preventing people from donating blood who are positive for malaria may result in too little blood being collected; in these cases, other strategies, such as treating donors or closely monitoring patients post-transfusion, may prove to be a better strategy.

malaria life cycle schematic CDC

Schematic of the malaria life cycle, courtesy of CDC (www.cdc.gov)

Annual Blood Examination Rate in Bengal

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QUESTION

What is the annual blood examination rate in West Bengal?

ANSWER

The annual blood examination rate (ABER) is a measure of the level of diagnostic monitoring activity. Data from 2007 suggested the ABER in West Bengal was around 5%, which is well below the level of 10% which is recommended for active surveillance and is the target of the National Vector Borne Disease Control Programme.

However, within West Bengal there is variation in the ABER both geographically and temporally. One study showed that in Naxalbari block in Darjeeling district, ABER in 2003 and 2004 was as low as 3.5%. The region experienced a malaria outbreak in late 2005, and the average ABER for this year soared as high as 16%; however, from January to May of 2005, before the transmission season and the outbreak, the ABER was only 0.5%! This means that monitoring efforts at the start of the outbreak were probably insufficient to detect the emergence of the outbreak and therefore delayed the process of responding to the emerging disease threat. Maintaining sufficient levels of malaria surveillance monitoring is particularly important in West Bengal, since this state is one of the major endemic centres for malaria in India, contribution about 11% of all malaria cases and about 6% of all cases of Plasmodium falciparum.

Lasting Headaches and Malaria

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QUESTION

I had malaria in July of 2011, returned to the U.S. in August, and had an occurrence of P. falciparum a little more than a month later. It was quickly treated, but I continue to get headaches. They occur about daily, and exercise induces a very severe headache. Is this a common lasting symptom of malaria?

ANSWER

Once successfully treated, malaria almost never has recurring or lasting side effects, nor are lasting headaches a known side effect of treatment with ACTs (artemisinin-based combination therapies, which is the recommended first-line treatment against P. falciparum). If your headaches are made worse through exertion, you should talk to your doctor about making sure they are not a symptom of a more serious condition.