Malaria FAQ

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Photo by Matthew Naythons, MD

Malaria is a serious and sometimes fatal disease caused by a parasite that infects a certain type of mosquito which feeds on humans. People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness. Four kinds of malaria parasites can infect humans: Plasmodium falciparum, P. vivax, P. ovale, and P. malariae. Infection with P. falciparum, if not promptly treated, may lead to death. Although malaria can be a deadly disease, illness and death from malaria can usually be prevented. [Read more…]

Malaria Countries and Map

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Geographic Distribution of Malaria Around the World

Where malaria is found depends mainly on climatic factors such as temperature, humidity, and rainfalls. Malaria is transmitted in tropical and subtropical areas, where:

  • Anopheles mosquitoes can survive and multiply
  • Malaria parasites can complete their growth cycle in the mosquitoes (“extrinsic incubation period”).

Temperature is particularly critical. For example, at temperatures below 20°C (68°F), Plasmodium falciparum (which causes severe malaria) cannot complete its growth cycle in the Anopheles mosquito, and thus cannot be transmitted. [Read more…]

Malaria Prevention

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Photo by Matthew Naythons, MD

Malaria prevention consists of a combination of mosquito avoidance measures and chemoprophylaxis. 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. [Read more…]

Malaria Treatment

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Malaria can be a severe, potentially fatal disease (especially when caused by Plasmodium falciparum) and treatment should be initiated as soon as possible.

Patients who have severe P. falciparum malaria or who cannot take oral medications should be given the treatment by continuous intravenous infusion.

Most drugs used in treatment are active against the parasite forms in the blood (the form that causes disease) and include:

  • chloroquine
  • atovaquone-proguanil (Malarone®)
  • artemether-lumefantrine (Coartem®)
  • mefloquine (Lariam®)
  • quinine
  • quinidine
  • doxycycline (used in combination with quinine)
  • clindamycin (used in combination with quinine)
  • artesunate (not licensed for use in the United States, but available through the CDC malaria hotline)

In addition, primaquine is active against the dormant parasite liver forms (hypnozoites) and prevents relapses. Primaquine should not be taken by pregnant women or by people who are deficient in G6PD (glucose-6-phosphate dehydrogenase). Patients should not take primaquine until a screening test has excluded G6PD deficiency.

How to treat a patient with malaria depends on:

  • The type (species) of the infecting parasite
  • The area where the infection was acquired and its drug-resistance status
  • The clinical status of the patient
  • Any accompanying illness or condition
  • Pregnancy
  • Drug allergies, or other medications taken by the patient

If you have or suspect you have malaria, you should contact your doctor immediately.

Source: Centers for Disease Control (CDC)

Malaria Prevention and Control

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Malaria Prevention

Prevention of malaria can aim at either:

  • preventing infection, by avoiding bites by parasite-carrying mosquitoes, or
  • preventing disease, by using antimalarial drugs prophylactically. The drugs do not prevent initial infection through a mosquito bite, but they prevent the development of malaria parasites in the blood, which are the forms that cause disease. This type of prevention is also called “suppression.” [Read more…]

Travel Information

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Malaria, a common and life-threatening disease, is a risk in tropical and subtropical areas of over 100 countries. An estimated 30,000 international travelers fall ill with the disease annually. Fever occurring in a traveller one week or more after entering a malaria risk area, and up to 3 months after departure, is a medical emergency that should be investigated urgently. Prompt diagnosis and correct treatment of malaria can mean the difference between life and death.

The ABCD’s of Malaria Protection

  • A: Awareness—Be aware of the Risk, the Incubation Period, and the Main Symptoms of malaria.
  • B: Bites—Avoid being bitten by mosquitos—especially between dusk and dawn.
  • C: Chemoprophylaxis—Take antimalarial drugs (chemoprophylaxis) to suppress infection where appropriate. (More information on antimalarial drugs).
  • D: Diagnosis—Immediately seek diagnosis and treatment if a fever develops one week or more after entering an area where there is malaria risk, and up to 3 months after departure.

Malaria in travellers can usually be prevented. All travellers to malarious regions should follow the ABCD principles listed above.

 

This information is intended for travelers who reside in the United States. Travelers from other countries may find this information helpful; however, because malaria prevention recommendations and the availability of antimalarial drugs vary, travelers from other countries should consult health care providers in their respective countries.

On this Page:

Countries with Malaria Risk

Travelers to sub-Saharan Africa have the greatest risk of both getting malaria and dying from their infection. However, all travelers to countries with malaria risk may get this potentially deadly disease.

Malaria is transmitted in

  • large areas of Central and South America
  • the island of Hispaniola (includes Haiti and the Dominican Republic)
  • Africa
  • Asia (including the Indian subcontinent, Southeast Asia and the Middle East)
  • Eastern Europe
  • and the South Pacific

What Determines Your Individual Risk

If you are traveling outside of the United States, Canada, and Western Europe, you may be at risk for malaria. All visitors to malaria risk areas are at risk of getting malaria; however, many factors determine the risk to an individual traveler. Even in the same locale, these factors can vary widely over time. From year to year, conditions such as amount of rainfall, the number of mosquitoes, and the number of infected persons in the area will change and may produce a different level of risk than previously seen.

Factors that determine a traveler’s risk include:

  • Unaware of malaria risk areas
    Many U.S. travelers, their healthcare providers, and tour companies may be unaware that their travel itinerary includes malaria risk areas.
  • Amount of malaria in the area to be visited
    Most malaria transmission occurs in rural areas, although malaria occurs in urban areas in many countries. Low altitudes with warm temperatures allow for larger populations of infective mosquitoes. Transmission is generally higher in Africa south of the Sahara than in most other areas of the world; in 2002, 73% of imported malaria cases among U.S. and foreign civilians occurred in persons who traveled to Africa.
  • Time of the year
    Seasons with more rainfall and higher temperatures will have more malaria transmission than colder, drier seasons. However, in most tropical and semi-tropical countries, transmission may occur even during cooler months or periods of less rainfall.
  • Type (species) of malaria parasite present in the area
    While all species of malaria parasites can make a person feel very ill, Plasmodium falciparum causes severe, potentially fatal malaria. Persons who travel to areas where P. falciparum malaria is present should be extra careful to take their antimalarial drug and to prevent mosquito bites.
  • Nighttime exposure to mosquito bites
    Because the mosquito that transmits malaria bites at night, travelers who are frequently out of doors between dusk and dawn will be at greater risk for malaria.
  • Preventive measures taken by travelers
    Individual measures, such as taking an effective antimalarial drug and preventing mosquito bites, are the most important factors in minimizing risk. While other risk factors may be difficult to change or avoid, travelers can greatly reduce their risk of malaria by following recommended travel precautions.
  • Immunity or lack of immunity to malaria
    Because malaria was eliminated from the United States in the late 1940s, most residents have never developed resistance (immunity) to the disease. Malaria infection in a non-immune person can quickly result in a severe and life-threatening illness.

In addition, many healthcare providers and laboratories in the United States rarely see cases of malaria and may be unfamiliar with the diagnosis and treatment of the disease, and this can delay effective treatment.

How to Protect Yourself

Know the Facts About Malaria

Every year, millions of United States residents travel to countries where malaria is present; about 800 cases of malaria are diagnosed in these returning travelers each year. From 1985-2002, 78 U.S. travelers died from malaria.

Persons who are traveling to malaria risk areas can almost always prevent this potentially deadly disease if they correctly take an effective antimalarial drug and follow measures to prevent mosquito bites.

Know the Symptoms

Despite these protective measures, travelers may become infected with malaria. Malaria symptoms can include:

  • fever
  • chills
  • headache
  • flu-like symptoms
  • muscle aches
  • fatigue
  • low blood cell counts (anemia)
  • yellowing of the skin and whites of the eye (jaundice)

If not promptly treated, infection with Plasmodium falciparum, the most harmful malaria parasite, may cause coma, kidney failure, and death.

When Symptoms Appear, Seek Immediate Medical Attention
Malaria is always a serious disease and may be a deadly illness. Travelers who become ill with a fever or flu-like illness either while traveling in a malaria-risk area or after returning home (for up to 1 year) should seek immediate medical attention and should tell the physician their travel history.

Additional Information Resources:

  • The CDC Travelers’ Health website provides information on protecting the health of international travelers, including detailed country-specific malaria prevention information plus recommendations for vaccinations (there is no malaria vaccine), food and water precautions, and safety information.
  • Preventing Malaria in Travelers ((PDF brochure, Size: 280 KB/8 pages

Counterfeit (“fake”) Drugs

In some countries (including those with malaria risk), drugs may be sold that are counterfeit (“fake”) or substandard (not made according to United States standards). Such drugs may not be effective. Purchase your antimalarial drugs before traveling overseas!

Source: World Health Organization (WHO); Centers for Disease Control (CDC)

Anopheles Mosquitoes

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Anopheles Mosquitoes

Diagram of Adult Female MosquitoDiagram of Adult Female Mosquito
 

Malaria is transmitted among humans by female mosquitoes of the genus Anopheles. Female mosquitoes take blood meals to carry out egg production, and such blood meals are the link between the human and the mosquito hosts in the parasite life cycle. The successful development of the malaria parasite in the mosquito (from the “gametocyte” stage to the “sporozoite” stage) depends on several factors. The most important is ambient temperature and humidity (higher temperatures accelerate the parasite growth in the mosquito) and whether the Anopheles survives long enough to allow the parasite to complete its cycle in the mosquito host (“sporogonic” or “extrinsic” cycle, duration 10 to 18 days). Differently from the human host, the mosquito host does not suffer noticeably from the presence of the parasites.

Thumbnail of the mosquito distribution map.Map of the world showing the distribution of predominant malaria vectors 

General Information

There are approximately 3,500 species of mosquitoes grouped into 41 genera. Human malaria is transmitted only by females of the genus Anopheles. Of the approximately 430 Anopheles species, only 30-40 transmit malaria (i.e., are “vectors”) in nature.

Geographic Distribution

Anophelines are found worldwide except Antarctica. Malaria is transmitted by different Anopheles species, depending on the region and the environment.

Anophelines that can transmit malaria are found not only in malaria-endemic areas, but also in areas where malaria has been eliminated. The latter areas are thus constantly at risk of re-introduction of the disease.

Anopheles freeborni mosquito pumping bloodAnopheles freeborni mosquito pumping blood

 

Powerpoint slide of Anopheles freeborni mosquito pumping blood

Life Stages

Like all mosquitoes, anophelines go through four stages in their life cycle: egg, larva, pupa, and adult. The first three stages are aquatic and last 5-14 days, depending on the species and the ambient temperature. The adult stage is when the female Anopheles mosquito acts as malaria vector. The adult females can live up to a month (or more in captivity) but most probably do not live more than 1-2 weeks in nature.

Eggs

Adult females lay 50-200 eggs per oviposition. Eggs are laid singly directly on water and are unique in having floats on either side. Eggs are not resistant to drying and hatch within 2-3 days, although hatching may take up to 2-3 weeks in colder climates.

Larvae

Mosquito larvae have a well-developed head with mouth brushes used for feeding, a large thorax, and a segmented abdomen. They have no legs. In contrast to other mosquitoes, Anopheles larvae lack a respiratory siphon and for this reason position themselves so that their body is parallel to the surface of the water.

Larvae breathe through spiracles located on the 8th abdominal segment and therefore must come to the surface frequently.

Top: Anopheles Egg; note the lateral floats. Bottom: Anopheles eggs are laid singlyTop: Anopheles Egg; note the lateral floats.
Bottom: Anopheles eggs are laid singly. 

Image of a Anopheles larva, floating parallel to water surfaceAnopheles Larva. Note the position, parallel to the water surface. 

The larvae spend most of their time feeding on algae, bacteria, and other microorganisms in the surface microlayer. They dive below the surface only when disturbed. Larvae swim either by jerky movements of the entire body or through propulsion with the mouth brushes.

Larvae develop through 4 stages, or instars, after which they metamorphose into pupae. At the end of each instar, the larvae molt, shedding their exoskeleton, or skin, to allow for further growth.

Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Tire tracks habitat.
Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Rice fields habitat
Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in very diverse habitats. Irrigation water habitat.

Larvae of Anopheles gambiae, the major malaria vector in Africa, can breed in diverse habitats. Three habitats are shown from left to right: tire tracks, rice fields, and irrigation water.

 

The larvae occur in a wide range of habitats but most species prefer clean, unpolluted water. Larvae of Anopheles mosquitoes have been found in fresh- or salt-water marshes, mangrove swamps, rice fields, grassy ditches, the edges of streams and rivers, and small, temporary rain pools. Many species prefer habitats with vegetation. Others prefer habitats that have none. Some breed in open, sun-lit pools while others are found only in shaded breeding sites in forests. A few species breed in tree holes or the leaf axils of some plants.

Graph of pupa of Anopheles, illustrating coma shapeAnopheles Pupa 

Pupae

The pupa is comma-shaped when viewed from the side. The head and thorax are merged into a cephalothorax with the abdomen curving around underneath. As with the larvae, pupae must come to the surface frequently to breathe, which they do through a pair of respiratory trumpets on the cephalothorax. After a few days as a pupa, the dorsal surface of the cephalothorax splits and the adult mosquito emerges.

The duration from egg to adult varies considerably among species and is strongly influenced by ambient temperature. Mosquitoes can develop from egg to adult in as little as 5 days but usually take 10-14 days in tropical conditions.

Schema of adult Anopheles seen from above, and from the side to show typical resting position) Anopheles Adults. Note (bottom row) the typical resting position. 

Adults

Like all mosquitoes, adult anophelines have slender bodies with 3 sections: head, thorax and abdomen.

The head is specialized for acquiring sensory information and for feeding. The head contains the eyes and a pair of long, many-segmented antennae. The antennae are important for detecting host odors as well as odors of breeding sites where females lay eggs. The head also has an elongate, forward-projecting proboscis used for feeding, and two sensory palps.

The thorax is specialized for locomotion. Three pairs of legs and a pair of wings are attached to the thorax.

The abdomen is specialized for food digestion and egg development. This segmented body part expands considerably when a female takes a blood meal. The blood is digested over time serving as a source of protein for the production of eggs, which gradually fill the abdomen.

Anopheles mosquitoes can be distinguished from other mosquitoes by the palps, which are as long as the proboscis, and by the presence of discrete blocks of black and white scales on the wings. Adult Anopheles can also be identified by their typical resting position: males and females rest with their abdomens sticking up in the air rather than parallel to the surface on which they are resting.

Adult mosquitoes usually mate within a few days after emerging from the pupal stage. In most species, the males form large swarms, usually around dusk, and the females fly into the swarms to mate.

Female Anopheles dirus FeedingFemale Anopheles dirus feeding 

Males live for about a week, feeding on nectar and other sources of sugar. Females will also feed on sugar sources for energy but usually require a blood meal for the development of eggs. After obtaining a full blood meal, the female will rest for a few days while the blood is digested and eggs are developed. This process depends on the temperature but usually takes 2-3 days in tropical conditions. Once the eggs are fully developed, the female lays them and resumes host seeking.

The cycle repeats itself until the female dies. Females can survive up to a month (or longer in captivity) but most probably do not live longer than 1-2 weeks in nature. Their chances of survival depend on temperature and humidity, but also their ability to successfully obtain a blood meal while avoiding host defenses.

Factors Involved in Malaria Transmission and Malaria Control

Understanding the biology and behavior of Anopheles mosquitoes can help understand how malaria is transmitted and can aid in designing appropriate control strategies. Factors that affect a mosquito’s ability to transmit malaria include its innate susceptibility to Plasmodium, its host choice, and its longevity. Factors that should be taken into consideration when designing a control program include the susceptibility of malaria vectors to insecticides and the preferred feeding and resting location of adult mosquitoes.

Preferred Sources for Blood Meals

One important behavioral factor is the degree to which an Anopheles species prefers to feed on humans (anthropophily) or animals such as cattle (zoophily). Anthrophilic Anopheles are more likely to transmit the malaria parasites from one person to another. Most Anopheles mosquitoes are not exclusively anthropophilic or zoophilic. However, the primary malaria vectors in Africa, An. gambiae and An. funestus, are strongly anthropophilic and, consequently, are two of the most efficient malaria vectors in the world.

Life Span

Once ingested by a mosquito, malaria parasites must undergo development within the mosquito before they are infectious to humans. The time required for development in the mosquito (the extrinsic incubation period) ranges from 10 to 21 days, depending on the parasite species and the temperature. If a mosquito does not survive longer than the extrinsic incubation period, then she will not be able to transmit any malaria parasites.

It is not possible to measure directly the life span of mosquitoes in nature. But indirect estimates of daily survivorship have been made for several Anopheles species. Estimates of daily survivorship of An. gambiae in Tanzania ranged from 0.77 to 0.84 meaning that at the end of one day between 77% and 84% will have survived. (Charlwood et al., 1997, Survival And Infection Probabilities of Anthropophagic Anophelines From An Area of High Prevalence of Plasmodium falciparum in Humans, Bulletin of Entomological Research, 87, 445-453).

Assuming this is constant through the adult life of a mosquito, less than 10% of female An. gambiae would survive longer than a 14-day extrinsic incubation period. If daily survivorship increased to 0.9, over 20% of mosquitoes would survive longer than a 14-day extrinsic incubation period. Control measures that rely on insecticides (e.g., indoor residual spraying) may actually impact malaria transmission more through their effect on adult longevity than through their effect on the population of adult mosquitoes.

Patterns of Feeding and Resting

Most Anopheles mosquitoes are crepuscular (active at dusk or dawn) or nocturnal (active at night). Some Anopheles mosquitoes feed indoors (endophagic) while others feed outdoors (exophagic). After blood feeding, some Anopheles mosquitoes prefer to rest indoors (endophilic) while others prefer to rest outdoors (exophilic). Biting by nocturnal, endophagic Anopheles mosquitoes can be markedly reduced through the use of insecticide-treated bed nets (ITNs) or through improved housing construction to prevent mosquito entry (e.g., window screens). Endophilic mosquitoes are readily controlled by indoor spraying of residual insecticides. In contrast, exophagic/exophilic vectors are best controlled through source reduction (destruction of the breeding sites).

Insecticide Resistance

Insecticide-based control measures (e.g., indoor spraying with insecticides, ITNs) are the principal way to kill mosquitoes that bite indoors. However, after prolonged exposure to an insecticide over several generations, mosquitoes, like other insects, may develop resistance, a capacity to survive contact with an insecticide. Since mosquitoes can have many generations per year, high levels of resistance can arise very quickly. Resistance of mosquitoes to some insecticides has been documented just within a few years after the insecticides were introduced. There are over 125 mosquito species with documented resistance to one or more insecticides. The development of resistance to insecticides used for indoor residual spraying was a major impediment during the Global Malaria Eradication Campaign. Judicious use of insecticides for mosquito control can limit the development and spread of resistance. However, use of insecticides in agriculture has often been implicated as contributing to resistance in mosquito populations. It is possible to detect developing resistance in mosquitoes and control programs are well advised to conduct surveillance for this potential problem.

Source: CDC