01 Jul 2014

Malaria

Malaria is transmitted to humans by Anopheles spp. mosquitoes and is widely distributed throughout tropical regions of the world Malaria

 

Key Messages

Malaria is a serious disease, transmitted by the bite of an infected mosquito.
Malaria is widely distributed throughout tropical regions of the world in Africa, Asia, Central and South America, Hispaniola, the Middle East and Oceania.
Malaria is preventable and curable if the illness is diagnosed and treated promptly.
Travellers are advised to follow an ABCD approach to preventing malaria (Awareness, Bite avoidance, Chemoprophylaxis (antimalarial tablets) – if appropriate, and Diagnosis).
Travellers visiting friends and family in areas of Africa account for the most number of cases returning to the UK; every opportunity should be taken to encourage the use of antimalarial tablets in this group.
Certain travellers are at increased risk of severe disease if they contract malaria; pregnant women, children, older people and those without a functioning spleen. Awareness of the ABCD approach to malaria prevention can be life saving.

Overview

Malaria is caused by protozoan parasites of the genus Plasmodium and is transmitted to humans by Anopheles spp. mosquitoes. There are five species of Plasmodium that cause disease in humans; P. falciparum, P. vivax, P. malariae, P. ovale and P. knowlesi. P. knowlesi is usually restricted to monkeys in South East Asia, but has been identified as a cause of malaria in humans [1].

In 2014, 97 countries and territories had ongoing malaria transmission, where approximately 3.2 billion people were exposed to the disease [2].

Risk areas

Figure 1: Countries and areas at risk of malaria transmission, 2013
Malaria risk
Source: World Health Organization, 2013
Please check our Country Information pages for individual country recommendations.

 

Malaria is widely distributed throughout tropical regions of the world in Africa, Asia, Central and South America, Hispaniola, the Middle East and Oceania. In 2013, the World Health Organization estimated there were 198 million cases of malaria and approximately 584,000 deaths worldwide, mostly amongst children under five years of age living in Africa [2].

The global prevalence of malaria species differs. While there is overlap, P. falciparum is most common in Africa, Hispaniola and Papua New Guinea and P. vivax is more common in the Indian subcontinent and Central America. South America and South East Asia have both species. P. ovale and P. malariae are less common, but are mostly reported in Africa. P. knowlesi occurs in South East Asia with cases widely distributed in Sabah and Sarawak in Malaysian Borneo, and peninsular Malaysia [1]. Cases have been reported from a number of other countries in South East Asia, and in travellers [3, 4].

Malaria-endemic areas can be classified into areas of stable and unstable malaria transmission. In stable areas, for example many countries of sub-Saharan Africa, malaria transmission is year-round with high rates of infection. The population, particularly adults, may therefore develop a degree of immunity and the majority of clinical cases occur in infants and children. In areas of unstable malaria, for example India, transmission tends to be seasonal with short epidemics of varying intensity. Malaria transmission in these unstable areas is less sustained, therefore communities have poor immunity and all age groups may be affected.

Risk for travellers

All travellers visiting malaria endemic regions are at risk of acquiring malaria, particularly migrants to the UK who were born in malaria risk areas and return to visit friends and relatives in their country of birth [5, 6]. Any immunity travellers may have acquired in their country of origin wanes rapidly on migration to a country with no risk of malaria; their UK-born children will have no protection from the disease.

Certain travellers are at increased risk of severe disease if they have malaria such as: pregnant women, those with an absent or dysfunctional spleen, children and older travellers [7]. Pregnant women are advised to avoid travel to malarious areas where possible, as they are particularly attractive to mosquitoes, have an increased risk of developing severe malaria and a higher risk of death compared to non-pregnant women [7]. Those who have no spleen or whose splenic function is severely impaired are also advised to avoid travel to affected areas where possible [7].

The risk of malaria varies according to season, geographic location, activities, type of accommodation, and the use of malaria prevention tablets and bite avoidance measures. Public Health England’s (PHE) Advisory Committee on Malaria Prevention (ACMP) Guidelines for malaria prevention in travellers from the UK are updated annually and provide country specific malaria risk information. This information is also available on our Country Information pages. Please be aware that other sources of advice may differ.

An individual risk assessment should be performed for each traveller to determine the appropriate preventative advice. Travellers should be reminded that even in lower risk malaria areas where ‘bite avoidance and awareness’ alone are usually recommended, special attention should be given to bite prevention and febrile illness must be taken seriously and investigated promptly [7]. Rarely, it may be appropriate to consider antimalarial medication for these lower risk areas if the individuals risk is considered to be high (e.g. due to a medical condition or planned activities).

Malaria in travellers from the United Kingdom

Around 1,500 cases of malaria are reported annually in travellers returning to or arriving in the UK from malaria endemic countries [8], with eight or less deaths reported each year since 2006 [8]. The majority of cases in the UK are caused by P. falciparum, the most severe form of malaria [5].

While most UK travellers acquiring malaria are of African heritage visiting friends and family, a UK study in 2012 identified that the risks of dying from malaria, once acquired, are highest in the elderly, tourists, and those presenting for medical help in areas of the UK where malaria less regularly seen and treated. [9]. Detailed Public Health England information about imported malaria in UK travellers is available here.

Transmission

Malaria is transmitted to humans via the bite of an infected female Anopheles mosquito. The female mosquito requires protein from blood in order for her eggs to mature. A diagram illustrating the life cycle of the malaria parasite is available in the ACMP Guidelines for malaria prevention in travellers from the UK

Anopheles mosquitoes generally bite between sunset and sunrise and are attracted to humans by several factors including heat, odour and carbon dioxide expired during breathing. The sporozoite stage of the malaria parasite migrates from the mosquito gut to the salivary glands, and is injected into humans when the mosquito takes a blood meal. Although the salivary glands can contain as many as 60,000 sporozoites, only a few are inoculated during feeding.

Once sporozoites enter the human they are rapidly carried to the liver where they infect liver cells and undergo further development. After a period of time that varies according to malaria species, parasites within liver cells mature and are released as merozoites. At this point they infect red blood cells and the symptoms of malaria occur. Two species of malaria, P. vivax and P. ovale, can persist in the liver for several months in a hypnozoite form.

Merozoites further develop within erythrocytes forming a schizont. When the schizont is fully developed, the red cell bursts and releases daughter merozoites that will infect other red cells. In order for malaria to infect a new person, sexual forms of the parasite termed gametocytes, must develop in infected red blood cells and be taken up by an Anopheles mosquito when it feeds. These develop into sporozoites in the mosquito, and the life cycle is completed.

Signs and symptoms

The incubation period of malaria (the time from injection of sporozoites to the onset of clinical symptoms) in P. falciparum is 7- 14 days, but can be longer where there is partial immunity or where the parasite has been suppressed by antimalarial tablets. In P. vivax or P. ovale infection, the incubation period is usually between 12 and 18 days, but can be several months or, rarely, years due to the emergence into the bloodstream from the liver of latent liver hypnozoites.

Malaria begins with a non-specific symptoms characterised by fever, headache, fatigue, abdominal discomfort and muscle aches [1]. Cough and diarrhoea can also be seen. Symptoms can progress to high fever and severe muscle aches and pains.

Although symptoms of malaria from all species can be disabling, illness with P. falciparum can progress rapidly and develop serious life-threatening complications if prompt treatment is not given. The most serious complication of falciparum malaria is malaria affecting the brain which can lead to coma and death. Other complications include kidney failure, low iron levels in the blood, low blood sugar, uncontrollable bleeding, low blood pressure, and excess fluid in the lungs. P. knowslei infections are usually uncomplicated but at least 10% of patients develop complications and 1–2% of cases have a fatal outcome [10].

The fever pattern in patients with P. vivax or P. ovale malaria may become cyclical, recurring every 48 hours. There are cold and hot phases: the cold stage with shivering lasts 15 to 60 minutes, and the hot stage lasts two to six hours, followed by profuse sweating. Although P. vivax can cause severe symptoms, fatalities are uncommon [11].

All travellers should be aware of the signs and symptoms of malaria and should be advised to seek immediate medical attention if these occur either whilst abroad or up to a year after their return.

Diagnosis and treatment

All travellers who present with fever and a history of travel to a malaria risk areas should be evaluated urgently for malaria. Clinical diagnosis is usually by thick and thin blood smears, which are examined by microscopy. An EDTA-anticoagulated venous blood sample should ideally be received in the laboratory within one hour of being taken [7]. Results should be confirmed on the same day and if positive, the patient should be referred to a specialist centre. If blood tests for malaria are negative, tests should be repeated daily for a further two days.

P. falciparum malaria is a medical emergency especially if complications have developed, and patients often require intensive therapy. Infection with any species of malaria should be treated promptly. Treatment of malaria should be in accordance with the ACMP malaria treatment guidelines [12] in consultation with an infection or tropical medicine unit.

The choice of drug treatment depends on the causative species and the likelihood of resistance of P. falciparum to chloroquine or other drugs. Travellers with P. falciparum malaria should be admitted to hospital where they can receive careful evaluation and monitoring. Travellers who develop malaria overseas in remote areas where appropriate supervised treatment may not be available, can consider self-treatment with emergency standby medication. Although rapid test kits have been given to travellers for help in the diagnosis of febrile episodes during travel, they are often not used correctly [13], and the ACMP do not recommend their use by travellers [7].

Emergency standby treatment is intended for travellers who believe they have malaria whilst overseas; it is not a replacement for malaria prevention tablets. Such travellers should still seek medical assistance as soon as possible if they develop a fever, in order for definitive diagnosis and treatment to be made. Guidelines for the use of emergency standby treatment are available in the ACMP Malaria prevention guidelines for travellers from the UK.

Preventing malaria

The prevention of malaria involves several steps that have been termed the A, B, C, D of malaria prevention [9]:

A -Awareness of the risk
B Bite prevention
C -Chemoprophylaxis (appropriate choice of antimalarial medication and compliance with the regime)
D -Diagnosis (prompt diagnosis and treatment without delay)

The choice of chemoprophylaxis to prevent malaria depends on the parasite species and whether or not there is resistance of P. falciparum to chloroquine or other drugs in the area to be visited.

Chemoprophylactic agents are either causal (directed at the liver phase of the malaria parasite life cycle) or suppressive (directed at the red blood cell phase of the malaria parasite life cycle). Information on the places in the life cycle targeted by the available chemoprophylatic agents is available in the ACMP Malaria prevention guidelines for travellers from the UK.

Choice of antimalarial medication should also be tailored to the individual, taking into account possible risks and benefits to the traveller. As part of an individual careful risk assessment, it is essential that a full clinical history is obtained, detailing current medication, significant health problems and any known drug allergies. A suggested risk assessment template is included with the ACMP guidelines [7].

Country specific advice regarding malaria is available on the Country Information pages.

Detailed advice regarding specific groups of travellers is available from the ACMP Guidelines for malaria prevention in travellers from the UK.

First Published :   01 Jul 2014
Last Updated :   29 Dec 2016

  1. White, N., Pukrittayakamee, S., Hien, T.T. et al. Malaria. Lancet 2014; 15 August; 383:723-35.
  2. World Health Organization. World Malaria Report 2014. [Accessed 17 September 2015]
  3. Antinori, S., Galimberti, L., Milazzo, L. Corbellino, M. Plasmodium knowlesi: The emerging zoonotic malaria parasite, Acta Tropica 125, 2013; 191– 201
  4. Cramer JP. Plasmodium knowlesi malaria: Overview Focussing on Travel- Associated Infections Curr Infect Dis Rep. 2015 Mar; 17(3):469.
  5. Public Health England. Malaria imported into the United Kingdom in 2013: Implications for those advising travellers. Health Protection Report. Vol 8,No 16, 25 April 2014. [Accessed 17 September 2015]
  6. Health Protection Agency. Foreign travel-associated illness – a focus on those visiting friends and relatives, 2008 report. [Accessed 17 September June 2015]
  7. Public Health England, Advisory Committee on Malarial Prevention, Guidelines for malaria prevention in travellers from the United Kingdom 2015. September 2015. [Accessed 17 September 2015]
  8. Public Health England. Imported malaria cases and deaths, United Kingdom: 1994 – 2013. Reviewed April 2014. [Accessed 17 September June 2015]
  9. Checkley, A.M., Smith, A., Smith, V. et al. Risk factors for mortality from imported falciparum malaria in the United Kingdom over 20 years: an observational study, BMJ 2012;344:e2116, [Accessed 17 September 2015]
  10. Millar SB, Cox-Sinh J. Human infections with Plasmodium knowlesi zoonotic malaria. Clin Microbiol Infect. 2015 Apr 2 pii : S1198743X (15)00381-X.doi : 10.1016/j.cmi.2015.03.017. [Epub ahead of print].
  11. Rahimi BA, Thakkinstian A, White NJ, et al. Severe vivax malaria: a systematic review and meta-analysis of clinical studies since 1900. Malar J. 2014 Dec 8; 13:481.
  12. Lalloo DG, Shingadia D, Bell D J, et al (on behalf of the HPA Advisory Committee on Malaria Prevention in UK Travellers). UK malaria treatment guidelines 2016. J Infect. 2016, 72: 635-649.
  13. Jelinek T. Malaria self- testing by travellers: opportunities and limitations. Travel Med Infect Dis. 2044 Aug-Nov: 2(3-4):143-8.

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