Where Does Malaria Occur?

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QUESTION

Where does malaria occur?

ANSWER

Malaria has at some stage or another occurred on every continent of the world except Antarctica. Currently, cases of human malaria are mainly found in Central and South America, parts of the Caribbean, sub-Saharan Africa, parts of the Middle East, south Asia, south-east Asia, and the Pacific Islands of Oceania. Control efforts, mainly consisting of reducing populations of vector mosquitoes, has eliminated transmission from North America, most of Europe, most of North Africa and parts of the Middle east and Asia. Currently, the vast majority of malaria mortalities occur in sub-Saharan Africa, and mainly in children under the age of five.

Malarone and Mefloquine for Malaria

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QUESTION

Which drug is better for kids for anti-malaria – Malarone or Mefloquine. I have heard about lot of side-effects of Mefloquine. So, which is a safer drug out of these two or is there any other drug with no side-effects? Is it important to take anti-malaria pills keeping in mind the side-effects?

ANSWER

Both drugs are considered safe for children, though Malarone (atovaquone-proguanil) should not be given to pregnant women or those nursing a child under 5kg. Malarone is also available in a pediatric form in some places, where the dose is reduced specifically for prescription to children under 40kg in weight. Personally, I took both Malarone and mefloquine (as Lariam) when I was a child, and experienced no side effects from either, though certainly many more people do report side effects from mefloquine, including disturbed sleep and hallucinations, or increased anxiety, and it is therefore not recommended for people with a history of psychiatric illness or disorders.

If this does not apply to you or your children, then it really is a matter of preference, cost and practicality. Malarone is generally more expensive than Lariam, needs to be taken every day, but only needs to be taken a few days before departing for the malarial area and for only one week after you return. Lariam, on the other hand, is only taken weekly (which can be an advantage with small children), but needs to be started 2 weeks before travel and for 4 weeks afterwards, which can make it less convenient for short trips.

The other thing to consider, finally, is where you are going—some forms of malaria found in south-east Asia are resistant to mefloquine, meaning it is not a suitable anti-malarial for travel in those areas, so Malarone would be a better choice in that circumstance. Both mefloquine and Malarone are suitable for travel in all other malarial areas.

Number of Species of Malaria

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QUESTION

I recently read an ISOS world malaria day poster saying 5 species of plasmodium cause malaria. I think that is confusing as we always talked about 4, ovale, vivax, falciparum and malaria….are they referring to the way we now split ovale into 2 sub species? or is this a typo on their part?

ANSWER

That is a really interesting question, and a good observation on your part! I imagine the fifth species they are referring to is Plasmodium knowlesi, which is found in parts of south-east Asia, with the majority of cases being reported from Borneo. Originally known only from macaque monkeys, it appears to be occurring more frequently in humans. However, it is not known whether this is a new host switch, or whether it is simply a matter of better detection methods—the morphology of P. knowlesi closely resembles that of P. falciparum in its early trophozoite stages, and P. malariae in later trophozoite and other life stage forms. Moreover, some molecular-based tests for P. knowlesi cross-react with other forms of malaria, such as P. vivax, leading to greater diagnostic confusion.

There is also a hypothesis that changes in land use in tropical forests may be resulting in greater human exposure to the vectors which carry P. knowlesi, which accounts for its increased recent prevalence in humans. P. knowlesi is the only known malaria in humans (and indeed, in all primates) with a 24-hour reproductive cycle, which means that without treatment, high levels of parasitaemia can accumulate rapidly in the blood, and lead to severe clinical symptoms. This makes its apparent emergence of great public health concern in south-east Asia. Luckily, at this point, P. knowlesi is completely susceptible to chloroquine treatment and other medications, and so is easily controlled once diagnosed.

One of our contributors, Christina Faust, wrote a blog post last year on P. knowlesi entitled Of Macaques and Men. More information on recent research about P. knowlesi can be found in the article, Monkeys Provide Malaria Reservoir for Human Disease in South-East Asia.

Distribution of Malaria

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QUESTION

Where does malaria mostly take place?

ANSWER

Malaria is mainly transmitted in tropical regions of the world; while some transmission does occur outside of the tropics, it tends to be seasonal in these areas (i.e. usually only during periods of high temperature/high rainfall). Within the tropics, malaria is found on all continents, though the highest number of cases is in Africa, which is also where over 90% of deaths due to malaria occur (of these, most are children under the age of 5). Outside Africa, the next highest levels of malaria are in India and south-east Asia and the western Pacific (such as Papua New Guinea).

How many countries have malaria?

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QUESTION

How many countries are malaria infected?

ANSWER

As of 2010, there were 108 countries which were listed as having endemic malaria—that is, malaria which was transmitted within the country. This includes 43 countries in Africa, 10 countries in south-east Asia, 13 countries in the Eastern Mediterranean (which includes most of Central Asia and parts of North and East Africa—90% of the malaria burden in this region is suffered by Sudan, Afghanistan, Pakistan and Somalia), 10 countries in the Western Pacific (though this region constitutes less than 1% of global malaria cases) and 23 malaria-endemic countries in the Americas.

Which Anti Malarial for South-East Asia?

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QUESTION

We are in our 70s and will be on a cruise from Siem Reap to Ho Chi Minh. Which anti malarial would be most effective for these areas?

ANSWER

The main thing to consider when travelling to south-east Asia is that there are areas where some of the malaria is resistant to mefloquine (commonly sold as Lariam), and therefore this drug is not appropriate as an anti-malarial in these regions.

Chloroquine resistance is also rife throughout the region, although this drug is rarely used as a malaria prophylactic drug. However, apart from this, the choice of anti-malarial depends to a large extent on personal preferences.

The two main types recommended by the CDC for travel to south-east Asia are atovaquone-proguanil (marketed commonly as Malarone) and doxycycline. The former is associated with very few side effects, is taken once a day, and needs to be taken for a week after returning from the malarial area. However it is also very pricey! Doxycycline, on the other hand, is very cheap, but many people experience high sun sensitivity which can lead to severe sun burn if sufficient care is not taken. It also has to be taken for a full four weeks after returning from the malarial area.

Current Status of Malaria

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QUESTION:

What is the current status on malaria? And does P.knowlesi spp. pose a greater threat compared to the others? Does the number malaria cases increase every year globally? Is P. knowlesi spp. more dangerous than the others and why?

ANSWER:

I’ll answer your question about Plasmodium knowlesi first. So far, it is considered a relatively minor source of malaria in humans, as its natural host are macaque monkeys and so it is usually thought of as a “zoonotic” disease.Between 2000-2008, there were only been about 400 reported cases of P. knowlesi, all restricted to south-east Asia, and mainly Borneo. These figures are low compared to other forms of malaria, such as P. falciparum, which in Africa alone accounts for millions of cases a year, and close to a million fatalities. However, there are some causes for concern with regards to P. knowlesi.

First of all, it appears to be an emerging human infection; the first cases were traced back to the 1960s, with the number of cases increasing in recent years. While some of this increase is likely the result of higher accuracy diagnosis and awareness about malaria, it is also hypothesised that the increasing population density in forested areas of south-east Asia may also be leading to greater numbers of people being exposed to this parasite. Secondly, although easily treated with anti-malarial drugs, the life cycle of P. knowlesi is such that it reproduces very rapidly in the human host, causing cycles of fever every 24 hours (a so-called “quotidian fever”). This means that the infection can progress rapidly, becoming severe in a matter of days, and therefore requiring prompt treatment. Finally, although locally restricted to south-east Asia, P. knowlesi has become the dominant form of malaria in some of these areas, notably Sarawak. As such, although currently not a major source of malaria in the global human population, it is locally important to public health and moreover, more research is needed to determine why the number of cases has been on the rise.

As for your questions about the status of malaria globally, the number of cases annually is estimated to be around 250 million. The vast majority of these are in Africa. Over 700,000 people, mainly children under five, die from malaria each year. As for whether the number of cases is increasing or decreasing, this is hard to determine. For one, a large number of cases are not reported every year, making accurate estimates difficult. Secondly, the world’s population is growing, and it is growing at the greatest rate in Africa, where the majority of malaria cases occur. As such, even if the proportion of people with malaria decreases over time, due to health initiatives such as distributing long-lasting insecticide treated bednets or free treatment, the total number of cases may still rise. Another problem we face in the fight against malaria is climate change: as the world’s patterns of rainfall and temperatures change, new areas become susceptible to malaria transmission, putting more people at risk. However, what is very encouraging is that deaths from malaria seem to be decreasing on a global scale.

Malaria No More is an organisation dedicated to eliminating deaths from malaria by the year 2015; more information about their methods and some of their success stories can be found on the Malaria No More website.

Monkeys Provide Malaria Reservoir for Human Disease in South-East Asia

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Macaque Monkey

Juvenile Macaque - Sandakan, Malaysia. Photo by Frances Williams (Sandakan-Travel.com).

Monkeys infected with an emerging malaria strain are providing a reservoir for human disease in Southeast Asia, according to recent research. The study confirms that the species has not yet adapted to humans and that monkeys are the main source of infection.

Malaria is a potentially deadly disease that kills over a million people each year. The disease is caused by malaria parasites, which are transmitted by infected mosquitoes and injected into the bloodstream.

There are five species of malaria parasite that are known to cause disease in humans, of which Plasmodium knowlesi is the most recently identified. Previously thought to only infect monkeys, researchers have shown that human P. knowlesi infections are widely distributed in Southeast Asia and that it is a significant cause of malaria in Malaysian Borneo. Until now, it was not clear whether the infection is transmitted from person to person, or is passed over from infected monkeys.

Researchers led by Professor Balbir Singh at the Malaria Research Centre, Universiti Malaysia Sarawak, collaborating with Sarawak State Health Department, St George’s University of London and the London School of Hygiene and Tropical Medicine, examined blood samples from 108 wild macaques from different locations around the Sarawak division in Malaysian Borneo. Their results reveal that 78% were infected with the P. knowlesi species of malaria parasite, and many were infected with one or more of four other species of monkey malaria parasites that have not yet been found in humans.

By comparing the molecular identity of the parasites from monkeys and those isolated from patients with knowlesi malaria, the team were able to build a picture of the evolutionary history of the parasite and its preferred host. Their analysis reveals that transmission of the knowlesi species is more common amongst wild monkeys, than from monkeys to humans, and that monkeys remain the dominant host.

“Our findings strongly indicate that P. knowlesi is a zoonosis in this area, that is to say it is passed by mosquitoes from infected monkeys to humans, with monkeys acting as a reservoir host,” explains Professor Singh. “However, with deforestation threatening the monkeys’ habitat and increases in the human population, it’s easy to see how this species of malaria could switch to humans as the preferred host. This would also hamper current efforts aimed at eliminating malaria.”

Based on the molecular data, the researchers estimate that the knowlesi malaria species evolved from its ancestral species between 98 000 and 478 000 years ago. This predates human settlement in the area, meaning that monkeys are mostly likely to have been the initial host for the parasite when the species first emerged. This estimate also indicates that the species is as old as, or older than, the two most common human malaria parasites, P. falciparum and P. vivax.

The study was funded by the Wellcome Trust, a global charitable foundation that supports biomedical research and the medical humanities. It was published today in the journal PLoS Pathogens.

Source: The Wellcome Trust