It is transmitted to humans through the bite of the Anopheles mosquito.
Once an infected mosquito bites a human, the parasites multiply in the host's liver before infecting and destroying red blood cells.
In some places, malaria can be treated and controlled with early diagnosis. However, some countries lack the resources to do this effectively.
Currently, no vaccine is licensed for use in the United States or globally, although one is available in Europe.
Malaria was eliminated from the U.S. in the early 1950s, but between 1,500 and 2,000 cases still occur each year, mostly in those who have recently traveled to malaria-endemic areas.
Here are some key points about the malaria. More detail is in the main article.
- Malaria is typically spread by mosquitoes.
- Symptoms resemble those of flu, but, without treatment, the effects can sometimes be long-term and fatal.
- Travelers, hikers, and campers can protect themselves with medication, pest control, clothing, and nets.
What is malaria?
Malaria is passed on by the Anopheles mosquito.
Over 100 types of Plasmodium parasite can infect a variety of species. They replicate at different rates, and this affects how quickly the symptoms escalate, and the severity of the disease.
Five types of Plasmodium parasite can infect humans. They are found in different parts of the world. Some cause a more severe type of malaria than others.
Malaria symptoms can be classified into two categories: uncomplicated and severe malaria.
This is diagnosed when symptoms are present, but there are no signs to indicate severe infection or dysfunction of the vital organs.
This form can become severe malaria if left untreated, or if the host has poor or no immunity.
Symptoms of uncomplicated malaria typically last 6 to 10 hours and recur every second day. Some strains of the parasite can have a longer cycle or cause mixed symptoms.
As symptoms resemble those of flu, they may be undiagnosed or misdiagnosed in areas where malaria is less common.
In uncomplicated malaria, symptoms progress as follows, through cold, hot, and sweating stages:
- a sensation of cold with shivering
- fever, headaches, and vomiting
- seizures sometimes occur in younger people with the disease
- sweats, followed by a return to normal temperature, with tiredness
In areas where malaria is common, many patients recognize the symptoms as malaria and treat themselves without visiting a doctor.
In severe malaria, clinical or laboratory evidence shows signs of vital organ dysfunction.
Symptoms of severe malaria include:
- fever and chills
- impaired consciousness
- prostration, or adopting a prone position
- multiple convulsions
- deep breathing and respiratory distress
- abnormal bleeding and signs of anemia
- clinical jaundice and evidence of vital organ dysfunction
Severe malaria can be fatal without treatment.
Malaria happens when a bite from the female Anopheles mosquito infects the body with Plasmodium. Only the Anopheles mosquito can transmit malaria.
The successful development of the parasite within the mosquito depends on several factors, the most important being humidity and ambient temperatures.
When an infected mosquito bites a human host, the parasite enters the bloodstream and lays dormant within the liver.
The host will have no symptoms for an average of 10.5 days, but the malaria parasite will begin multiplying during this time.
The new malaria parasites are then released back into the bloodstream, where they infect red blood cells and multiply further. Some malaria parasites remain in the liver and are not released until later, resulting in recurrence.
An unaffected mosquito becomes infected once it feeds on an infected individual. This restarts the cycle.
Early diagnosis is critical for a patient's recovery.
Anyone showing signs of malaria should be tested immediately.
The World Health Organization (WHO) strongly advise confirmation of the parasite through microscopic laboratory testing or by a rapid diagnostic test (RDT), depending on the facilities available.
No combination of symptoms can reliably distinguish malaria from other causes, so a parasitological test is vital for identifying and managing the disease.
In some malaria-endemic areas, such as sub-Saharan Africa, the disease's severity can cause mild immunity in a large proportion of the local population.
As a result, some people carry the parasites in their bloodstream but do not fall ill.
Treatment aims to eliminate the Plasmodium parasite from the patient's bloodstream.
Those without symptoms may be treated for infection to reduce the risk of disease transmission in the surrounding population.
Artemisinin-based combination therapy (ACT) is recommended by the WHO to treat uncomplicated malaria.
Artemisinin is derived from the plant Artemisia annua, better known as sweet wormwood. It is known for its ability to rapidly reduce the concentration of Plasmodium parasites in the bloodstream.
ACT is artemisinin combined with a partner drug. The role of artemisinin is to reduce the number of parasites within the first 3 days of infection, while the partner drugs eliminate the rest.
Expanding access to ACT treatment worldwide has helped reduce the impact of malaria, but the disease is becoming increasingly resistant to the effects of ACT.
In places where malaria is resistant to ACT, treatment must contain an effective partner drug.
The WHO has warned that no alternatives to artemisinin are likely to become available for several years.
There are several ways to keep malaria at bay.
Research to develop safe and effective global vaccines for malaria is ongoing, with one vaccine already licensed for use in Europe. No vaccine is yet licensed in the U.S.
It is essential to seek medical attention for suspected symptoms of malaria as early as possible.
Prevention: Advice for travelers
Travelers to places where malaria is prevalent should take precautions, for example, using mosquito nets.
While malaria is not endemic to the U.S., travel to many countries around the world entails a risk.
Travelers are advised to:
- find out what the risk of malaria is in the country and city or region they are visiting
- ask their doctor what medications they should use to prevent infection in that region
- obtain antimalarial drugs before leaving home, to avoid the risk of buying counterfeit drugs when away
- consider the risk for individual travelers, including children, older people, pregnant women, and the existing medical conditions of any travelers
- ensure they will have access to insect repellants, insecticides, pre-treated bed nets, and appropriate clothing
- be aware of the symptoms of malaria
In emergency situations, local health authorities in some countries may carry out "fogging," or spraying areas with pesticides similar to those used in household sprays.
The WHO points out that these are not harmful for people, as the concentration of pesticide is only strong enough to kills mosquitoes.
While away, travelers should, where possible, avoid situations that increase the risk of being bitten by mosquitoes. Precautions include taking an air-conditioned room, not camping by stagnant water, and wearing clothes that cover the body at times when mosquitoes are most likely to be around.
For a year after returning home, the traveler may be susceptible to symptoms of malaria. Donating blood may also not be possible for some time.
Anopheles mosquito, the vector for malaria
Malaria is one of the most common infectious diseases and a great public health problem worldwide, particularly in Africa and south Asia. About three billion people are at risk of infection in 109 countries. Each year, there are an estimated 250 million cases of malaria leading to approximately one million deaths, mostly in children under five years of age. The organism that causes the most dangerous form of malaria is a microscopic parasite called Plasmodium falciparum.
This parasite is transmitted by mosquito species belonging to the Anophelesgenus and only by females of those species.
There is growing international agreement on how best to use prevention and treatment methods that are available. The most effective prevention measures include the use of mosquito bed nets treated with long-lasting insecticides – to avoid the mosquito bites and to kill the mosquitoes – and spraying the inside walls of houses with similar insecticides to kill malaria-carrying mosquitoes. The most effective treatment for malaria consists in using a combination of several anti-malarial drugs, one of which is a derivative of artemisinin. Preventive treatment of pregnant women with anti-malarial drugs can also reduce the harmful effects of malaria both on the mother and on the unborn child.
Several international organisations have set up ambitious objectives for large-scale malaria control. The target set by the Word Health Organization (WHO) in 2005 is to offer malaria prevention and treatment services by 2010 to at least 80% of the people who need them. By doing so, it aims to reduce at least by half the proportion of people who become ill or die from malaria by 2010 and at least by three quarters by 2015 compared to 2005.
It is vital to monitor malaria trends to see if malaria control campaigns are being effective, and to make improvements.
The WHO World Malaria Report 2008 estimates the number of malaria cases and deaths for the period 2001-2006 in affected countries and investigates whether or not WHO recommendations are being implemented. It evaluates progress made against the disease it also describes the sources of funding and reviews the impact of malaria control programmes. The aim of the report is to support the development of effective national malaria control programmes.
This text is a summary of: WHO, World Malaria Report (2008),