How Many Types of Human Malaria?

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QUESTION:

How many types of malaria infect humans?

ANSWER:

There are four main types of malaria which infect humans: Plasmodium falciparum, P. vivax, P. malariae and P. ovale. P. ovale additionally can be split into two sympatric sub-species, P. o. curtisi and P. o. wallikeri. Each of these five kinds has a subtly different life cycle which results in slight variations in symptoms and also in treatment. For more information on this, check out the Q&As on malaria symptoms and malaria treatment; CDC is also a site worth checking out.

Additionally to the four species above, there are observations of a number of other Plasmodium species being able to infect humans, although much less frequently. The most reported of these is P. knowlesi, found in SE Asia, which usually infects macaque monkeys but is capable of crossing over into humans and causing severe quotidien malaria, and may even result in death. The number of cases of P. knowlesi appears to be on the rise in some regions, although the cause of this is not quite clear. For an introduction to P. knowlesi, you should read Christina Faust’s blog.

The list of other species of Plasmodium that have been reported to infect humans (sometimes only experimentally in the lab) includes P. brasilianum, P. cynomolgi, P. eylesi, P. inui, P. rhodiani, P. schwetzi, P. semiovale, P. simium and P. tenue.

Mosquitoes with Malaria

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QUESTION:

Do mosquitoes with malaria get sick like people do?

ANSWER:

That’s a great question! As far as I know, the jury is still out in terms of what overall effect being infected with malaria has on mosquitoes, and to a large extent, it appears to vary due to lots of factors, such as the compatibility between the mosquito and the particular type of malaria parasite, the intensity of malarial infection, and even environmental conditions, to name but a few. However, what is clear is that mosquitoes don’t seem to get ‘sick’ like we do, with fevers, chills and the like—their immune system is just too different from ours! Instead, with mosquitoes, it’s more a question of whether malaria decreases their lifespan, reduced their reproductive success, or other such effects.

A meta-analysis (Ferguson & Read, 2002, ‘Why is the effect of malaria parasites on mosquito survival still unresolved?’, in Trends in Parasitology) of studies that looked on the effect of malaria on mosquito survival demonstrated that 41% of studies reported a detrimental effect of malaria on mosquitoes, whereas 59% reported no effect (none reported a positive effect, which is interesting).

Also worth noting is that the length of the study seemed to have an effect on whether it would report a detrimental effect; this might be due to early stages of infection with malaria not having a negative impact on the host, while the malaria parasite is developing; then, once it is mature, it may be that the parasite’s virulence towards its host increases. Similarly, at this stage in its life cycle, the parasite might induce changes in the mosquito’s behaviour, encouraging it to feed more, which can result in higher mortality to the mosquito (think of swatting away annoying, biting mosquitoes, whereas you’re less likely to go for ones that leave you alone!).

More recently, a study by EJ Dawes and colleagues at Imperial College, London (2009, ‘Anopheles mortality is both age- and Plasmodium-density dependent: Implications for malaria transmission, in Malaria Journal) found evidence for the age of the mosquito and the intensity of malaria parasitism influencing mortality of the insects. Similarly, another research group found that infected female mosquites had significantly lower fecundity than non-infected mosquitoes (Gray & Bradley, 2006, ‘Malarial infection in Aedes aegypti: Effects on feeding, fecundity and metabolic rate’, in Parasitology). These examples begin to swing the balance of the debate in favour of malaria having a negative impact on mosquitoes, at least at certain points in the timeline of an infection (i.e. near the beginning, and then after parasite maturation).

You might ask why mosquitoes that are commonly infected with malaria don’t become resistant to infection, given that they seem to suffer ill-effects when they are parasitised—well, some recent research may have provided the answer to that one. Researchers looking at population growth rates in malaria-susceptible mosquitoes versus those resistant to infection noticed significantly slower growth rates in the resistant population, suggesting that in terms of reproduction, resistance at a population level might come at a cost to growth (Voordouw et al., 2009, ‘Rodent malaria-resistant strains of the mosquito, Anopheles gambiae, have slower population growth than -susceptible strains’, in BMC Evolutionary Biology). However, there may be ways in which this effect can be by-passed, in order to control malaria transmission at the level of the mosquito; one group of researchers recently published the results of a study, where they showed that when resistant and susceptible male mosquitoes rae released into a population of females (bearing in mind only the females feed on blood, and so males are not implicated in transmission), the females tend to mate first with the earlier-hatching resistant males, and moreover, lay a greater number of eggs with these males! So it may be that research on the effect of malaria on mosquitoes can be used in the future to decrease malaria transmission, which would be a hugely positive step for public health in many parts of the world.

It would be great if any malaria researchers out there would comment on the above answer, especially if there are more up-to-date examples of research on the effect of malaria on mosquitoes!

Drinking Milk While Infected with Malaria

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QUESTION:

Can a malaria-infected person drink milk?

ANSWER:

As far as I know, there isn’t a problem with drinking milk while suffering from malaria. In fact, it is generally a good idea to keep as hydrated as possible while feverish (although water or diluted juice would probably be better for hydration). There is also some evidence that drinking milk can settle the stomach while taking medication for malaria, such as chlorquine.

If there are medical professionals who read this and can comment further on the benefits/problems of drinking milk while suffering from malaria, then please comment below!

Malaria Self-Diagnosis

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QUESTION:

I live in Nigeria and was wondering if there are ways to find out if I malaria without going to the doctor or a hospital?

ANSWER:

The current “gold-standard” for malaria diagnosis, at least of active infections, is through microscropy, where a trained technician looks at a droplet of your blood on a slide, and sees if any of your red blood cells are infected with the malaria parasite. Given the expertise required for this procedure, it is usually only available through a doctor or in a hospital setting. Moreover, this technique is not reliable for very low numbers of parasites, though most active malaria infections will be positively diagnosed.

However, in the last ten years, there has been a rise in the availability and effectiveness of so-called rapid diagnostic tests (RDTs) for malaria, which can be self-administered and so are able to be bought in a pharmacy and used at home. There are a wide variety of these tests, which work by using antibodies to detect the antigens produced by the malaria parasites. As such, the tests seem to be able to detect even low levels of parasitaemia, and in some cases can even tell you which kind of malaria you have. The tests usually come with all necessary materials, which include a lancet for pricking the fingertip for a drop of blood, although you should always check that everything is within the packaging (I have bought tests in Uganda which came without the buffer solution; this had to be purchased separately in this case). The WHO maintains a list of currently available RDTs (PDF).

Make sure the test you purchase is suitable for the type of malaria that is found in your region; many only test for P. falciparum, for example, which might not be appropriate for a region with high levels of P. vivax or other species.

How many people die from malaria annually?

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QUESTION:

How many people die each year from malaria?

ANSWER:

There is a wide range of estimates for the total number of deaths caused by malaria, but the World Health Organisation generally reports “around a million” deaths each year from the disease, out of somewhere between 300-500 million cases. In total, it is estimated that 3.3 billion people are at risk from malaria, which is almost half the world’s population!

One reason for the high uncertainty in total numbers of deaths is that many malaria cases go unreported, and those at highest risk are often living in the world’s poorest parts of the world, where health services are patchy and underfunded. Moreover, throughout the world, children are some of the highest risk cases for severe malaria, and deaths are sometimes attributed to other causes which may be confounded by malaria, such as malnutrition, diarrhoea or respiratory infections.

What is certain is that many of those deaths from malaria are entirely preventable, through the use of insecticide treated bednets, improvements in local health infrastructure and encouraging early diagnosis and treatment of malarial episodes.

What are the three stages of a malaria attack?

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QUESTION:

What are the three stages of a typical malaria attack?

ANSWER:

I’m not entirely clear as to what you’re asking with this question; do you mean the stages of infection within the human host, or the successive changes in the symptoms during the fever cycles that characterise a malarial episode?

If you mean the latter, then the three typical stages of symptoms during a malaria attack are characterised by an initial feeling of coldness, which is indicative of the early stages of the fever. This develops into the patient feeling much, much warmer, and even uncomfortably hot—at this point, the patient’s fever can spike dramatically, up to over 40 degrees C. The body combats this fever by sweating profusely—these sweats constitute the third stage of the attack, and have the effect of gradually bringing the patient’s temperature down.

These three stages are repeated at intervals of 24, 48 or 72 hours, depending on the type of malaria. This is due to the cyclical and coordinated bursting of red blood cells, releasing the next life stage of the malaria parasite, and which causes the bulk of the fever in patients.

If you intended to ask about the stages of infection during the life cycle of the malaria parasite, the image below (from CDC), is a very clear and useful guide to the incredibly complex life cycle of Plasmodium species.

generalised malaria life cycle

Generalised life cycle of the malaria parasite (courtesy of CDC: www.cdc.gov)




 

 

Malaria – Free Bednets?

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QUESTION:

Why do people have to pay for the bed nets?  I think that is mean to the people and they should get them for free.

ANSWER:

You have hit on a very important and on-going debate in the malaria control community. In many places around the world, organisations such as UNICEF have distributed free, insecticide-treated bednets, and especially to mothers—pregnant women and children under five are the groups most at risk from dying from malaria.

In 2010, UNICEF reported that together with its partners (WHO, the EU and the World Bank, to name a few) 5.5 million free bednets have been distributed in DR Congo alone. Similarly, in Mozambique, the Malaria Consortium has been working in a partnership with DFID and the public sector to distribute 400,000 bednets to pregnant women as part of an ante-natal service, again targeting some of the most at-risk people.

However, you are right to say that in some cases, people have to pay for bednets; in some of the poorest countries in the world, this can seem like an unjustifiable expense. However, there are some arguments in favor of having people buy their bednets.

For example, some people argue that a purely public donation initiative is unsustainable, and in order to have an on-going distribution campaign, the private sector has to be involved at some level, and this usually means charging a fee for each bednet. Moreover, forcing people to buy their own nets would free up donor funds for other purposes. Similarly, it is thought in some circles that having payment encourages suppliers to continue producing and selling nets. Finally, there are suggestions that purchasing a bednet increases their value to the recipient, who subsequently uses their net more frequently and more reliably in the manner in which it is intended (and not, for example, as a spare fishing net, as I’ve seen in parts of Uganda!).

I believe a study in Malawi showed that by asking people in urban areas, who have a bit more disposable income, to purchase full-price bednets, the program was able to generate sufficient funds to offer bednets at a highly subsidized cost in rural, poorer areas of the country; by asking people to purchase the nets, the program believed bednet usage among its recipients was higher overall, than if the nets had been given out for free.

I think the organization that tried this approach was called PSI (Population Services International)—they also offered nurses a small monetary incentive to sell bed nets (at the small sum of 50 cents each) to the rural women who attended pre-natal clinics, thus encouraging them to offer the nets widely to pregnant women.

As the final word, a study in Kenya recently showed that as costs for services such as bednets increased, demand for the service among the poorest sectors of the population declined sharply. Instead, it seemed most economical and efficient to target high-risk groups with free bednets, who are also incentivized to use the product properly and value the protection it confers, such as pregnant women in ante-natal settings, rather than doling them out to the community at large.

So we’re back to where I started with this response; the great job that many organizations out there are doing in distribution insecticide-treated bednets to the people who need it the most, and who can’t afford to buy them themselves, although it is worth bearing in mind that alternative models of bednet funding and distribution might prove equally beneficial and potentially more sustainable, at least in certain areas.

I’m also going to ask Hugo Gouvras to weigh in on this one—he works for Malaria No More, an organization that has recently launched an innovative mechanism for accelerating funding provision for bednet distribution to Africa. Hopefully he can update anything that I have said which is old news, and provide additional information!

Is it rare to die if you get malaira?

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QUESTION:

Is it rare to die if you get malaria? I know that every 45 seconds somebody dies from malaira, I just want to know if it is rare or not. What percentage of people who get malaria die?

ANSWER:

There isn’t an easy answer to this question.  The risk of death depends on the kind of malaria you get, your previous exposure to malaria and how fast you get treatment.  P. falciparum is mostly found in Africa and parts of Asia,  is the most serious and deadly type of malaria, and children are especially at risk of dying from it.  In your question you mentioned someone dying every 45 seconds….that quote comes from the World Health Organization where experts estimate that in Africa, a child dies from malaria every 45 seconds.

Globally, international agencies estimate that between 300-500 million people get malaria every year and about 1 million people die from it. So it isn’t a rare occurrence to die from malaria but it should be because we have the knowledge to prevent and treat the disease which would drastically lower the number of deaths.   People can take drugs as prevention and avoid mosquito bites by sleeping under a treated bednet; using mosquito repellent and avoiding being outside from dawn to dusk when mosquitoes bite.  If you do get malaria, recognizing the symptoms and getting treatment quickly can be life saving.

However even the estimated 1,000,000  malaria deaths each year may not be accurate because it’s not easy to get trusted statistics. This is because many people (especially in rural Africa and Asia) don’t go to the hospitals or clinics when they get sick—either they don’t recognize the symptoms or they can’t reach a clinic or hospital in time.  Even if they do get treatment, oftentimes medical reporting systems are weak.

Another issue is that sometimes deaths are not attributed to malaria but to another disease—for example in a young child a malaria death may be attributed to an acute respiratory infection which can also present with a high fever.

So in a nut shell, malaria is a serious disease, but we know how to lower the risk of getting it and we know that in most cases prompt treatment will prevent death.   The challenge is to raise awareness in countries with malaria to promote prevention measures and to improve access to effective health care.

Traveling and Pregnant

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QUESTION:

Hi, I am 3 months pregnant but thinking about going on vacation to Belize in a few weeks time. Should I think about taking something against malaria?

ANSWER:

It’s good you asked because getting malaria while pregnant can be much more serious than when not pregnant, and can cause terrible problems to both you and your baby.  Therefore, it is always advisable to consult your own health care provider before traveling.

The good news is that while there is malaria in Belize it is not found everywhere and where it is found, it is not resistant to chloroquine, a drug considered safe to use during pregnancy.

According to the US Centers for Disease Control (CDC),   Belize City and the islands where tourists mostly visit are largely malaria free, and the risk of getting malaria in these areas is ‘low’. So, if you are heading to Belize City or a resort on one of the islands, you may just want to follow practical advice to avoid mosquito bites: sleep in a screened room and under an insecticide treated bed-net, avoid being outside between dusk and dawn, and if you are, wear long-sleeves and long pants or skirt, and use mosquito repellent (containing DEET, and especially during pregnancy, in my opinion a  roll-on repellent if preferable to a spray to avoid inhaling the chemicals).

However, if you are heading off the beaten track, you should take all the mosquito bite precautions mentioned above but also take chloroquine as prophylaxis. Take chloroquine (500 mg tablet containing 300 mg base drug) one time a week starting 1 – 2 weeks before traveling to an area with malaria. Continue taking one pill once a week (on the same day and the same time) while in country and for another 4 weeks after leaving the malaria area.

 

Malaria in Brazil

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QUESTION:

Is there Malaria in Brazil? If so, what pills do I need to take?

ANSWER:

Yes, there is malaria in many parts of Brazil, and more than one type: about 75% of cases in Brazil are caused by Plasmodium vivax, whereas the rest are from infections with P. falciparum, the more acute and dangerous species of malaria. Brazil does have good information as to the distribution of malaria across the country; in terms of affected states, the full list is as follows:

Acre, Amapa, Amazonas, Maranhao (western part), Mato Grosso (northern part), Para (except Belem City), Rondonia, Roraima, and Tocantins.

This includes cities within the above districts, such as Boa Vista, Macapa, Manaus, Maraba, Porto Velho and Santarem, and particularly on the outskirts where transmission is highest. It is worth noting that malaria is not considered to be a problem in the region of Iguassu Falls.

In terms of malaria prevention, the CDC recommends Larium (mefloquine is the generic name), Malarone (atovaquone or proguanil are the generic names) or doxycycline, due to the presence of chloroquine-resistant P. falciparum in some areas. Deciding between which of these to take depends on a number of factor, including cost, known side-effects, and, not least of all, personal preference. For a discussion on the pros and cons of these various form of prophylaxis, check out the discussion “Malaria Prophylaxis” on this website.