Malaria Parasite Picture

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QUESTION

Please show parasites pictures.

ANSWER

The first plate below shows various stages of the life cycle of Plasmodium falciparum, the most deadly form of malaria, and the most commonly found type in sub-Saharan Africa. Below that, a similar plate shows a series of images of Plasmodium vivax, the most widespread type of malaria.

A: The stages of P. falciparum. 1: Normal red cell; Figs. 2-18: Trophozoites (among these, Figs. 2-10 correspond to ring-stage trophozoites); Figs. 19-26: Schizonts (Fig. 26 is a ruptured schizont); Figs. 27, 28: Mature macrogametocytes (female); Figs. 29, 30: Mature microgametocytes (male). Illustrations from: Coatney GR, Collins WE, Warren M, Contacos PG. “The Primate Malarias”. Bethesda: U.S. Department of Health, Education and Welfare; 1971. Reproduced here courtesy of the CDC (www.cdc.gov)

 

 

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.

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)

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.

Malaria Mosquito

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QUESTION

Which mosquito causes malaria?

ANSWER

Malaria mosquito vector map CDC

Map of the main global mosquito vectors of malaria (image courtesy of CDC)

It is important to note that mosquitoes do not CAUSE malaria—the disease itself is caused by microscopic, single-celled animals called Plasmodium. These Plasmodium parasites live and reproduce inside the mosquito, and when the mosquito bites a person, the parasites are transferred into that person’s blood via the mosquito’s saliva. If another mosquito bites a person with malaria, they will pick up the parasites from the person’s blood, and the cycle continues.

Malaria parasites are simply transmitted by mosquitoes, and specifically of the genus Anopheles, of which a variety of different species are capable of transmitting it to humans. In Africa, the species most responsible for transmission is An. gambiae, which actually consists of a group of very similar and closely related species; the group as a whole is known as the An. gambiae species complex. An. funestus is also a wide-spread and important vector species in Africa. Below is a map, courtesy of the CDC, which shows the distribution of some of the main malaria vector mosquitoes worldwide.

Causes of malaria

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QUESTION:

What are the causes of malaria?

ANSWER:

Malaria is caused by parasites of the genus Plasmodium. These are single-celled animals known as protozoans (from the Greek ‘protos’ and ‘zoia’ which together mean ‘first animal’) and they are transmitted via mosquitoes that feed on blood; the parasites need both mosquito and human hosts to complete their life cycle (see below a graphic of the complete life cycle, courtesy of CDC). In the process of reproducing, the malaria parasites destroy human red blood cells, which is what causes the clinical symptoms of disease that the patient experiences, such as fever, headaches and nausea.

Malaria life cycle CDC

Generalized malaria life cycle (courtesy of CDC: www.cdc.gov)

There are four main species of Plasmodium that infect humans: P. falciparum, P. vivax, P. malariae and P. ovale. P. falciparum causes the most severe manifestations of the disease and is responsible for the majority of human deaths from malaria. There is a fifth type of malaria, P. knowlesi, which usually infects macaque monkeys but has been known to pass into humans as well.

For more on this, please see Christina Faust’s excellent blog post about her research.

Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Malaria

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Partial mosquito-proofing of houses with screens and ceilings has the potential to reduce indoor densities of malaria mosquitoes. We wish to measure whether it will also reduce indoor densities of vectors of neglected tropical diseases.

Methodology: The main house entry points preferred by anopheline and culicine vectors were determined through controlled experiments using specially designed experimental huts and village houses in Lupiro village, southern Tanzania. The benefit of screening different entry points (eaves, windows and doors) using PVC-coated fibre glass netting material in terms of reduced indoor densities of mosquitoes was evaluated compared to the control.

Findings: 23,027 mosquitoes were caught with CDC light traps; 77.9% (17,929) were Anopheles gambiae sensu lato, of which 66.2% were An. arabiensis and 33.8% An. gambiae sensu stricto. The remainder comprised 0.2% (50) An. funestus, 10.2% (2359) Culex spp. and 11.6% (2664) Mansonia spp. Screening eaves reduced densities of Anopheles gambiae s. l. (Relative ratio (RR) = 0.91; 95% CI = 0.84, 0.98; P = 0.01); Mansonia africana (RR = 0.43; 95% CI = 0.26, 0.76; P<0.001) and Mansonia uniformis (RR = 0.37; 95% CI = 0.25, 0.56; P<0.001) but not Culex quinquefasciatus, Cx. univittatus or Cx. theileri. Numbers of these species were reduced by screening windows and doors but this was not significant.

Significance: This study confirms that across Africa, screening eaves protects households against important mosquito vectors of filariasis, Rift Valley Fever and O’Nyong nyong as well as malaria. While full house screening is required to exclude Culex species mosquitoes, screening of eaves alone or fitting ceilings has considerable potential for integrated control of other vectors of filariasis, arbovirus and malaria.

Author Summary: Mosquito vectors that transmit filariasis and several arboviruses such as Rift Valley Fever, Chikungunya and O’Nyong nyong as well as malaria co-occur across tropical Africa. These diseases are co-endemic in most rural African countries where they are transmitted by the same mosquito vectors. The only control measure currently in widespread use is mass drug administration for filariasis. In this study, we used controlled experiments to evaluate the benefit of screening the main mosquito entry points into houses, namely, eaves, windows and doors.

This study aims to illustrate the potential of screening specific house openings with the intention of preventing endophagic mosquitoes from entering houses and thus reducing contact between humans and vectors of neglected tropical diseases. This study confirms that while full house screening is effective for reducing indoor densities of Culex spp. mosquitoes, screening of eaves alone has a great potential for integrated control of neglected tropical diseases and malaria.

Citation: Ogoma SB, Lweitoijera DW, Ngonyani H, Furer B, Russell TL, et al. (2010) Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors. PLoS Negl Trop Dis 4(8): e773. doi:10.1371/journal.pntd.0000773

Editor: Neal D. E. Alexander, London School of Hygiene and Tropical Medicine, United Kingdom

Funding: SBO was supported by a scholarship kindly provided by Valent Bioscience Corporation. This study was also supported by the Centers for Disease Control and Prevention and the United States Agency for International Development through the U.S. President’s Malaria Initiative (Award Number 621-A-00-08-0007-00), the Addessium Foundation (Reenwijk, The Netherlands) and a Research Career Development Fellowship (076806) provided to GFK by the Wellcome Trust. The funders of this study had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Copyright: © 2010 Ogoma et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

More information: Full text: Screening Mosquito House Entry Points as a Potential Method for Integrated Control of Endophagic Filariasis, Arbovirus and Malaria Vectors (PDF)