Malaria

Between 2000 and 2019, there was a marked reduction in global malaria case incidence and mortality rates:

• The malaria case incidence rate (cases per 1,000 population at risk) fell from 80 in 2000 to 57 in 2019, while total malaria cases declined from 238 million in 2000 to 229 million in 2019. In this same period, the population in sub-Saharan Africa, which accounts for more than 90 per cent of the global burden of malaria, increased from 665 million to over one billion.
• The mortality incidence rate (deaths per 100,000 population at risk) was reduced from 25 in 2000 to 10 in 2019, while the total number of deaths fell from 736,000 in 2000 to 409,000 in 2019.

Of the estimated 1.5 billion malaria cases and 7.6 million malaria deaths averted globally since 2000, most cases (82 per cent) and deaths (94 per cent) averted were in the African Region, followed by the South-East Asia Region (10 per cent cases and 3 per cent related deaths).

In spite of the decreases, malaria continues to take a heavy toll on pregnant women and children, particularly in Africa.

Coverage gaps are an important contributor to non-achievement of the WHO Global Technical Strategy targets, particularly in hard-to-reach, conflict-affected and marginalized communities. While expanded access to WHO-recommended malaria control interventions has played a critical role in reducing the global burden of the disease since 2000, a large proportion of the population at risk of malaria – particularly in the WHO African region – continues to lack access to prevention, diagnosis and treatment.

The following are standard case definitions to allow national health authorities to interpret data in an international context. However, during an outbreak case definitions may be adapted to the local context and the Red Cross Red Crescent should use those agreed/established by national health authorities. NB: Consider that during community-based surveillance, volunteers should use broad (simplified) case definitions (referred to as community case definitions) to recognize most or all possible cases, provide relevant risk communication and appropriate actions and encourage them to seek care. Other actors such as healthcare workers or investigators studying the cause of a disease, on the other hand, can use more specific case definitions that may require laboratory confirmation.

Case definitions for malaria control (different case definitions are used for malaria elimination):

Malaria case: Occurrence of malaria infection in a person in whom the presence of malaria parasites in the blood has been confirmed by a diagnostic test.

Suspected malaria case: Illness is suspected by a health worker to be due to malaria, generally based on the presence of fever with or without other symptoms. These criteria vary according to local circumstances and are established by national malaria programmes. All suspected cases of malaria should be tested by either microscopy or a rapid diagnostic test (RDT).

Presumed (not tested) malaria case: Case suspected of being malaria and not confirmed by a diagnostic test. Such designation is reserved for situations in which a diagnostic test cannot be performed in a timely manner.

Confirmed malaria case: A suspected case of malaria in which the parasite called Plasmodium has been detected in a diagnostic test. WHO case definition source of information: https://apps.who.int/iris/bitstream/handle/10665/208815/WHO_HTM_GMP_2016.6_eng.pdf

• Malaria epidemics tend to occur where endemicity is relatively low, reflecting the infrequency of transmission.
• Partial immunity is developed over years of exposure, and while it never provides complete protection, it does reduce the risk that malaria infection will cause severe disease. For this reason, most malaria deaths in Africa occur in young children, whereas in areas with less transmission and low immunity, all age groups are at risk.
• Environmental factors such as altitude and tropical climate are optimal for the Anopheles mosquitoes to breed.
• Human related factors such as socio-economic status, health access, migration, gender, vector control activities and land use (irrigation, deforestation, swamp drainage and living near breeding sites).
• Health status of the population: malnutrition can weaken children's immunity and can increase the level of malaria morbidity and mortality; HIV has been associated with an increased level of malaria transmission.
• Emergence and spread of drug-resistant parasites and insecticide-resistant mosquito populations.
• Population migration, reduced health systems access and quality, socio-economic pressure as population grows.
• Environments where mosquitoes breed such as tropical rainforests, humid, and semi-humid environments, as well as around bodies of stagnant water in and close to human habitations in urban settings.
• Epidemics can occur when people with low immunity move into areas with intense malaria transmission to find work or as refugees.

Attack rates will vary from one outbreak to another. In case of an outbreak, consult the latest information provided by health authorities.

It depends on the level of natural immunity of the population. Infections are often asymptomatic.

• In terms of age, children under five years of age are the most vulnerable group affected by malaria.
• Pregnant women.
• People living with HIV/AIDS or other immunosuppressed diseases
• Populations moving from non-endemic to endemic areas
• Populations living in previously non-endemic areas experiencing outbreaks due to climate, ecological or other factors.
• Non-immune migrants, mobile populations and travellers.

Malaria is caused by a parasite called Plasmodium of which there are five species.

P. falciparum and P. vivax pose the greatest threat to humans.

Vector-borne: The Plasmodium parasite is transmitted to humans through the bite of infected mosquitoes (vector) of the Anopheles genus.

Humans.

Vector-borne:

• Anopheles mosquitoes transmit malaria. The female Anopheles mosquito ingests malaria parasites (gametocytes) from an infected individual when taking a blood meal. These parasites grow and multiply in the mosquito for 10—18 days becoming a different form of the parasite (sporozoites), which are transmitted to an uninfected individual during blood feeding.  Only female Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken from an infected person.
• The mosquitoes usually bite between sunset and sunrise (during the night).

The incubation period in most cases varies from 7 to 30 days. The shorter periods are observed most frequently with P. falciparum and the longer ones with P. malariae.

Antimalarial drugs taken for prophylaxis by travellers can delay the appearance of malaria symptoms by weeks or months, long after the traveller has left the malaria-endemic area. Such long delays between exposure and development of symptoms can result in misdiagnosis or delayed diagnosis because of reduced clinical suspicion by the healthcare provider.

With appropriate treatment, symptoms of malaria usually go away quickly, with a cure within two weeks. Without proper treatment, malaria episodes (fever, chills, sweating) can return periodically over a period of years and mean that the person is still carrying malaria parasites which can be transmitted to others through the Anopheles vector as described above.

Malaria disease is typically classified into “uncomplicated” and “severe”:

“Uncomplicated” malaria typically presents with the following signs and symptoms:

• Fever
• Chills
• Sweats
• Headaches
• Nausea and vomiting
• Body aches
• General malaise

In countries where cases of malaria are infrequent, these symptoms may be attributed to influenza, a cold or other common infections, especially if malaria is not suspected. Conversely, in countries where malaria is frequent, residents often recognize the symptoms as malaria and treat themselves without seeking diagnostic confirmation (“presumptive treatment”).

• “Severe” cases present with weakness, loss of consciousness, severe anaemia, acute respiratory and renal failure.
• Children with “severe” malaria frequently develop one or more of the following symptoms: severe anaemia, respiratory distress in relation to metabolic acidosis, or cerebral malaria. In adults, multi-organ involvement is also frequent.

Dengue fever, Zika virus infection, chikungunya, pneumonia, influenza, Ebola virus infection, trypanosomiasis and other haemorrhagic infections.

• Microscopy.
• In areas where microscopy is not available, rapid diagnostic tests (RDTs) are useful to aid diagnosis and guide public health action.

Please refer to the appropriate local or international guidelines for clinical management. All clinical management including the administration of any treatment or vaccine should be conducted by health professionals.

• A list of medicines maintained by the World Health Organization includes first-line treatments in endemic countries for uncomplicated and severe malaria, as well as for prevention and treatment during pregnancy.
• A vaccine has been available since October 2021 for people at risk. The World Health Organization (WHO) is recommending widespread use of the RTS,S/AS01 (RTS,S) malaria vaccine among children in sub-Saharan Africa and in other regions with moderate to high P. falciparum malaria transmission.

• An immune response occurs following natural infection. However complete protective immunity does not develop, because repeated infections occur in individuals living in endemic areas.
• The vaccine demonstrates high-level efficacy of 77 per cent over 12 months of follow-up.