Anopheles Mosquito

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QUESTION

Why is it only the female anopheles mosquito alone can cause malaria but not the male anopheles mosquito or any other mosquitoes?

ANSWER

Malaria is actually caused by a single-celled parasite called Plasmodium—it is transmitted via the bite of a female mosquito, of the genus Anopheles, as she takes a blood meal from a human (or other mammal) host. Male mosquitoes do not feed on blood (they only feed on nectar), whereas females need the nutrients from blood in order to produce their eggs; as such, only female Anopheles transmit mosquito.

Why only Anopheles are able to transmit malaria to humans is interesting—birds and reptiles also can get Plasmodium (though different species than those that infect humans and other mammals), and these kinds of malaria can also be transmitted by other kinds of mosquitoes, such as Aedes and Culex. Other closely related blood parasites can even be transmitted by other flying insects, such as sand flies and black flies. However, it is true that only Anopheles can transmit human malaria.

Malaria Prevention

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QUESTION

What are the ways in which you can prevent yourself from being infected with malaria?

ANSWER

Malaria prevention consists of a combination of mosquito avoidance measures (since malaria is transmitted by infected mosquitoes) and chemoprophylaxis (medication to prevent the establishment of malaria in your body, if you do get bitten). Although very efficacious, none of the recommended interventions are 100% effective.

Mosquito Avoidance Measures

  • Because of the nocturnal feeding habits of Anopheles mosquitoes, malaria transmission occurs primarily between dusk and dawn.
  • Contact with mosquitoes can be reduced by remaining in well-screened areas, using mosquito bed nets (preferably insecticide-treated nets), using a pyrethroid-containing flying-insect spray in living and sleeping areas during evening and nighttime hours, and wearing clothes that cover most of the body.
  • All travelers should use an effective mosquito repellent.
  • The most effective repellent against a wide range of vectors is DEET (N,N-diethylmetatoluamide), an ingredient in many commercially available insect repellents. The actual concentration of DEET varies widely among repellents. DEET formulations as high as 50% are recommended for both adults and children older than 2 months of age (see the Protection Against Mosquitoes, Ticks, and Other Insects and Arthropods section later in this chapter). DEET should be applied to the exposed parts of the skin when mosquitoes are likely to be present.
  • In addition to using a topical insect repellent, a permethrin-containing product may be applied to bed nets and clothing for additional protection against mosquitoes.

Chemoprophylaxis

      • All currently recommended primary chemoprophylaxis regimens involve taking a medicine before travel, during travel, and for a period of time after leaving the malaria endemic area. Beginning the drug before travel allows the antimalarial agent to be in the blood before the traveler is exposed to malaria parasites.
      • Presumptive antirelapse therapy (also known as terminal prophylaxis) uses a medication towards the end of the exposure period (or immediately thereafter) to prevent relapses or delayed-onset clinical presentations of malaria caused by hypnozoites (dormant liver stages) of P. vivax or P. ovale. Because most malarious areas of the world (except the Caribbean) have at least one species of relapsing malaria, travelers to these areas have some risk for acquiring either P. vivax or P. ovale, although the actual risk for an individual traveler is difficult to define. Presumptive anti-relapse therapy is generally indicated only for persons who have had prolonged exposure in malaria-endemic areas (e.g., missionaries, volunteers).
      • In choosing an appropriate chemoprophylactic regimen before travel, the traveler and the health-care provider should consider several factors. The travel itinerary should be reviewed in detail and compared with the information on where malaria transmission occurs within a given country to determine whether the traveler will actually be traveling in a part of the country where malaria occurs and if significant antimalarial drug resistance has been reported in that location.
      • The resistance of P. falciparum to chloroquine has been confirmed in all areas with P. falciparum malaria except the Caribbean, Central America west of the Panama Canal, and some countries in the Middle East. In addition, resistance to sulfadoxine–pyrimethamine (e.g., Fansidar) is widespread in the Amazon River Basin area of South America, much of Southeast Asia, other parts of Asia, and in large parts of Africa. Resistance to mefloquine has been confirmed on the borders of Thailand with Burma (Myanmar) and Cambodia, in the western provinces of Cambodia, in the eastern states of Burma (Myanmar), on the border between Burma and China, along the borders of Laos and Burma, and the adjacent parts of the Thailand–Cambodia border, as well as in southern Vietnam.
      • Additional factors to consider are the patient’s other medical conditions, medications being taken (to assess potential drug–drug interactions), the cost of the medicines, and the potential side effects.

The medications recommended for chemoprophylaxis of malaria may also be available at overseas destinations. However, combinations of these medications and additional drugs that are not recommended may be commonly prescribed and used in other countries. Travelers should be strongly discouraged from obtaining chemoprophylactic medications while abroad. The quality of these products is not known, and they may not be protective and may be dangerous. These medications may have been produced by substandard manufacturing practices, may be counterfeit, or may contain contaminants. Additional information on this topic can be found in an FDA document

Purchasing Medications Outside the United States.

Can I Catch Malaria from Someone?

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QUESTION

My fiancee contracted malaria a few years ago. It was diagnosed as recurring. Could I contract malaria from the infected person, I have had similar symptoms which last a day or two, recurring with regular two week intervals, of which the most concerning are malaise, fever, stiff neck, headaches and severe pains over abdomen spreading into my mid back. What should I do?

ANSWER

Malaria cannot be directly transmitted between two people—it is almost always transmitted by the bite of an infected mosquito, and cannot survive at low temperatures (under about 17 degrees C). In some very rare cases, malaria can be transmitted through organ transplant, blood transfusion and pregnancy, since it infects red blood cells. Given these restrictions, it is close to impossible that you contracted malaria from your fiancee, and you should talk to your doctor about alternative explanations.

Also, if your girlfriend has recurring malaria, she should talk to her doctor about taking primaquine. While not suitable for everyone (namely people with G6DP deficiency should not take it), it can kill the dormant stages of the malaria parasite and prevent recurrence.

Malaria Causes

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QUESTION

What are the causes of malaria?

ANSWER

Malaria is caused by a parasite called Plasmodium, which is transmitted via the bites of infected mosquitoes. In the human body, the parasites multiply in the liver, and then infect red blood cells. Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About 1 week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito’s saliva and are injected into the person being bitten.

Please see “Malaria Symptoms and Causes” for more.

Sexual Intercourse During Malaria Infection

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QUESTION

Can one have sexual intercourse during malaria infection?

Can malaria be transmitted by sexual intercourse?

ANSWER

Malaria cannot be transmitted by sexual intercourse. It is usually transmitted via the bite of an infected mosquito. Because the parasites infect red blood cells, malaria can also be transmitted via blood transfusion (if the blood is not screened beforehand), organ transplant, and from a mother to her unborn baby, either during childbirth or via the placenta.

Malaria in Mosquitoes

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QUESTION

Why can’t mosquitoes become sick of malaria? What do they have in their system that prevent them from becoming sick yet they transmit the disease to humans?

ANSWER

First of all, mosquitoes do get “sick” when infected with malaria, though not in the same way as humans. This is due to the major differences between human and mosquito physiology and also differences in the life stage of the malaria parasite between the different hosts.

Humans get sick from malaria because the malaria parasite, when inside the human host, sequentially infects red blood cells, multiplying inside them and then destroying them. This process of destruction and the resultant debris in the blood results fever and other symptoms (some of which are exacerbated by the body’s immune response).

Mosquitoes are insects, and do not have blood in the same way as humans. Instead, in the mosquito, the malaria parasites differentiate into male and female life stages (called gametocytes) which fuse into the mosquitoes gut. After further reproduction, they eventually produce sporozoites that rupture out of the mosquito gut wall and migrate to the salivary glands, where they can be infected into a new human host.  

Mosquitoes also have a very different immune system to humans, and so the concept of “sick” is not the same for them as for humans. However, there is a lot of evidence that infection with malaria results in reduced reproductive success for the mosquito, as well as lower survival. This could be due to protective responses on the part of the mosquito, but also could be mediated by the malaria parasite, by diverted resources towards its own development that could have been used for mosquito reproduction or survival.

Malaria Transmission and Deaths in the United States

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QUESTION

How do you get malaria? How does malaria come to the United States? How many people have died from malaria?

ANSWER

Malaria is caused by infection with single-celled parasites called Plasmodium. There are five different species which infect humans; of these, Plasmodium falciparum is the most deadly. The Plasmodium parasites are transmitted to humans through the bite of an infected female Anopheles mosquito; when these mosquitoes bite a human, they transfer some of the parasites in their saliva.

After undergoing one set of multiplications in the liver, the malaria parasites are released into the blood, where they repeatedly infect and destroy red blood cells, multiplying in the process. These cycles of infection and destruction of red blood cells cause the cyclical fever that is characteristic of malaria. Eventually, the parasite produces new types of cells, called gametocytes; if the patient is then bitten by another mosquito, the mosquito can take up gametocytes as well as blood when it feeds, and the cycle continues.

Malaria used to be relatively common in the United States, though usually only occurring during the summer months and restricted to the warm, wet south-eastern region. However, a concerted control campaign in the 1940s, focusing mainly on vector control (i.e. killing mosquito and reducing their opportunities for breeding) swiftly led to the eradication of malaria from the US.

Nowadays, virtually all malaria cases in the US are imported from abroad, whereby people get infected when traveling to other countries, but are only diagnosed as having malaria when they return home. There are about 1,000 cases of malaria reported each year in the US, and most of these were actually caught outside the US. Very rarely, an Anopheles mosquito will bite one of these travelers once they have returned from abroad, and therefore have the potential to transmit malaria within the US. However, due to a strong public health network and good access to malaria diagnosis and treatment, these events rarely lead to more than a handful of cases before they are quickly treated and transmission eliminated again.

The World Health Organisation estimates that last year, approximately 700,000 people died of malaria. Of these, 90% were in sub-Saharan Africa, and the vast majority were children under the age of 5.

Three Stages of Malaria

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QUESTION

What are the three stages of malaria?

ANSWER

The three parts of the malaria life cycle are known as the exo-erythrocytic cycle, the erythrocytic cycle and the sporogonic cycle. The first two of these take place in the human (or other mammal) host, while the third occurs in the mosquito vector. The below diagram, courtesy of the CDC, shows the complete life cycle of malaria in more detail.

malaria life cycle CDC

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

Is malaria infectious?

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QUESTION

Is malaria infectious or noninfectious?

ANSWER

Malaria is considered an infectious disease because it can be transmitted from one person to another, via the bite of an infected mosquito. Since the parasite that causes malaria is passed through the blood, it can also be transmitted via organ transplant, blood transfusion, or via pregnancy (so-called “congenital” malaria).

What countries have malaria?

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QUESTION

In which countries can it be found?

ANSWER

Malaria is found in many parts of Africa, Latin America, Asia, and Oceania. The exact distribution depends on climatic variables (namely heat and sufficient rainfall, for the development of the mosquitoes which transmit malaria) and also how successful a particular country or region has been at controlling malaria.

For example, malaria was once found in parts of the U.S. and Europe, but successful campaigns to control mosquitoes and treat cases led to elimination of transmission. The same is true in other parts of the world; for example, in Malaysia, transmission is successfully controlled in Kuala Lumpur, but malaria can still be found in many parts of the surrounding countryside.

Please visit the CDC website for an interactive map of malaria distribution around the world.