Malaria - Key Facts
Key facts
Malaria is a life-threatening disease caused
by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes.
In 2015, 91 countries and areas had ongoing
malaria transmission.
Malaria is preventable and curable, and
increased efforts are dramatically reducing the malaria burden in many places.
Between 2010 and 2015, malaria incidence among
populations at risk (the rate of new cases) fell by 21% globally. In that same
period, malaria mortality rates among populations at risk fell by 29% globally
among all age groups, and by 35% among children under 5.
The WHO African Region carries a
disproportionately high share of the global malaria burden. In 2015, the region
was home to 90% of malaria cases and 92% of malaria deaths.
Malaria is caused by Plasmodium parasites. The
parasites are spread to people through the bites of infected female Anopheles mosquitoes,
called "malaria vectors."
There are 5 parasite species that cause
malaria in humans, and 2 of these species – P. falciparum and P.
vivax –
pose the greatest threat.
P. falciparum is
the most prevalent malaria parasite on the African continent. It is responsible
for most malaria-related deaths globally.
P. vivax is
the dominant malaria parasite in most countries outside of sub-Saharan Africa.
Symptoms
Malaria is an acute febrile illness. In a
non-immune individual, symptoms usually appear 10–15 days after the infective
mosquito bite.
The first symptoms – fever, headache, and
chills– may be mild and difficult to recognize as malaria. If not treated
within 24 hours, P.
falciparum malaria
can progress to severe illness, often leading to death.
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. In malaria endemic areas, people may develop partial immunity,
allowing asymptomatic infections to occur.
Who is at risk?
In 2015, nearly half of the world's population
was at risk of malaria.
Most malaria cases and deaths occur in
sub-Saharan Africa. However, South-East Asia, Latin America and the Middle East
are also at risk.
In 2015, 91 countries and areas had ongoing malaria
transmission.
Some population groups are at considerably
higher risk of contracting malaria, and developing severe disease, than others.
These include infants, children under 5 years
of age, pregnant women and patients with HIV/AIDS, as well as non-immune
migrants, mobile populations and travellers.
National malaria control programmes need to
take special measures to protect these population groups from malaria
infection, taking into consideration their specific circumstances.
Disease burden
According to the latest WHO estimates,
released in December 2016, there were 212 million cases of malaria in 2015 and
429 000 deaths.
Between 2010 and 2015, malaria incidence among
populations at risk fell by 21% globally; during the same period, malaria mortality
rates among populations at risk decreased by 29%.
An estimated 6.8 million malaria deaths have
been averted globally since 2001.
The WHO African Region continues to carry a
disproportionately high share of the global malaria burden.
In 2015, the region was home to 90% of malaria
cases and 92% of malaria deaths. Some 13 countries – mainly in sub-Saharan
Africa – account for 76% of malaria cases and 75% deaths globally.
In areas with high transmission of malaria,
children under 5 are particularly susceptible to infection, illness and death;
more than two thirds (70%) of all malaria deaths occur in this age group.
Between 2010 and 2015, the under-5 malaria
death rate fell by 29% globally. However malaria remains a major killer of
children under five years old, taking the life of a child every two minutes.
Transmission
In most cases, malaria is transmitted through
the bites of female Anopheles mosquitoes.
There are more than 400 different species of Anopheles mosquito;
around 30 are malaria vectors of major importance.
All of the important vector species bite
between dusk and dawn. The intensity of transmission depends on factors related
to the parasite, the vector, the human host, and the environment.
Anopheles mosquitoes
lay their eggs in water, which hatch into larvae, eventually emerging as adult
mosquitoes.
The female mosquitoes seek a blood meal to
nurture their eggs.
Each species of Anopheles mosquito
has its own preferred aquatic habitat; for example, some prefer small, shallow
collections of fresh water, such as puddles and hoof prints, which are abundant
during the rainy season in tropical countries.
Transmission is more intense in places where
the mosquito lifespan is longer (so that the parasite has time to complete its
development inside the mosquito) and where it prefers to bite humans rather
than other animals.
The long lifespan and strong human-biting
habit of the African vector species is the main reason why nearly 90% of the
world's malaria cases are in Africa.
Transmission also depends on climatic
conditions that may affect the number and survival of mosquitoes, such as
rainfall patterns, temperature and humidity. In many places, transmission is
seasonal, with the peak during and just after the rainy season.
Malaria epidemics can occur when climate and
other conditions suddenly favour transmission in areas where people have little
or no immunity to malaria.
They can also occur when people with low
immunity move into areas with intense malaria transmission, for instance to
find work, or as refugees.
Human immunity is another important factor,
especially among adults in areas of moderate or intense transmission
conditions.
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.
Prevention
Vector control is the main way to prevent and
reduce malaria transmission. If coverage of vector control interventions within
a specific area is high enough, then a measure of protection will be conferred
across the community.
WHO
recommends protection for all people at risk of malaria with effective malaria
vector control.
Two forms of vector control –
insecticide-treated mosquito nets and indoor residual spraying – are effective
in a wide range of circumstances.
Insecticide-treated mosquito nets
Long-lasting insecticidal nets (LLINs) are the
preferred form of insecticide-treated mosquito nets (ITNs) for public health
programmes. In most settings, WHO recommends LLIN coverage for all people at
risk of malaria.
The most cost-effective way to achieve this is
by providing LLINs free of charge, to ensure equal access for all.
In parallel, effective behaviour change
communication strategies are required to ensure that all people at risk of
malaria sleep under a LLIN every night, and that the net is properly maintained.
Indoor spraying with residual insecticides
Indoor residual spraying (IRS) with
insecticides is a powerful way to rapidly reduce malaria transmission.
Its potential is realized when at least 80% of
houses in targeted areas are sprayed. Indoor spraying is effective for 3–6
months, depending on the insecticide formulation used and the type of surface
on which it is sprayed. In some settings, multiple spray rounds are needed to
protect the population for the entire malaria season.
Antimalarial drugs
Antimalarial medicines can also be used to
prevent malaria.
For travellers, malaria can be prevented
through chemoprophylaxis, which suppresses the blood stage of malaria
infections, thereby preventing malaria disease. For pregnant women living in
moderate-to-high transmission areas,
WHO recommends intermittent preventive
treatment with sulfadoxine-pyrimethamine, at each scheduled antenatal visit
after the first trimester.
Similarly, for infants living in
high-transmission areas of Africa, 3 doses of intermittent preventive treatment
with sulfadoxine-pyrimethamine are recommended, delivered alongside routine
vaccinations.
In 2012, WHO recommended Seasonal Malaria
Chemoprevention as an additional malaria prevention strategy for areas of the
Sahel sub-region of Africa.
The strategy involves the administration of
monthly courses of amodiaquine plus sulfadoxine-pyrimethamine to all children
under 5 years of age during the high transmission season.
Insecticide resistance
Much of the success in controlling malaria is
due to vector control. Vector control is highly dependent on the use of
pyrethroids, which are the only class of insecticides currently recommended for
ITNs or LLINs.
In
recent years, mosquito resistance to pyrethroids has emerged in many countries.
In some areas, resistance to all 4 classes of insecticides used for public
health has been detected.
Fortunately, this resistance has only rarely
been associated with decreased efficacy of LLINs, which continue to provide a
substantial level of protection in most settings.
Rotational use of different classes of
insecticides for IRS is recommended as one approach to manage insecticide
resistance.
However, malaria-endemic areas of sub-Saharan
Africa and India are causing significant concern due to high levels of malaria
transmission and widespread reports of insecticide resistance.
The use of 2 different insecticides in a
mosquito net offers an opportunity to mitigate the risk of the development and
spread of insecticide resistance; developing these new nets is a priority.
Several promising products for both IRS and
nets are in the pipeline.
Detection of insecticide resistance should be
an essential component of all national malaria control efforts to ensure that
the most effective vector control methods are being used.
The choice of insecticide for IRS should
always be informed by recent, local data on the susceptibility of target
vectors.
To ensure a timely and coordinated global
response to the threat of insecticide resistance, WHO worked with a wide range
of stakeholders to develop the "Global Plan for Insecticide Resistance
Management in Malaria Vectors (GPIRM)", which was released in May 2012.
Diagnosis and treatment
Early diagnosis and treatment of malaria
reduces disease and prevents deaths. It also contributes to reducing malaria
transmission.
The best available treatment, particularly for P.
falciparum malaria,
is artemisinin-based combination therapy (ACT).
WHO recommends that all cases of suspected
malaria be confirmed using parasite-based diagnostic testing (either microscopy
or rapid diagnostic test) before administering treatment.
Results of parasitological confirmation can be
available in 30 minutes or less.
Treatment, solely on the basis of symptoms
should only be considered when a parasitological diagnosis is not possible. M
ore detailed recommendations are available in
the "WHO
Guidelines for the treatment of malaria", third edition, published in
April 2015.
Antimalarial drug resistance
Resistance to antimalarial medicines is a
recurring problem. Resistance of P. falciparum to previous generations of
medicines, such as chloroquine and sulfadoxine-pyrimethamine (SP), became widespread
in the 1950s and 1960s, undermining malaria control efforts and reversing gains
in child survival.
WHO recommends the routine monitoring of
antimalarial drug resistance, and supports countries to strengthen their
efforts in this important area of work.
An ACT contains both the drug artemisinin and
a partner drug. In recent years, parasite resistance to artemisinin has been
detected in 5 countries of the Greater Mekong subregion: Cambodia, Lao People’s
Democratic Republic, Myanmar, Thailand and Viet Nam.
Studies have confirmed that artemisinin
resistance has emerged independently in many areas of this subregion.
In 2013, WHO launched the Emergency response
to artemisinin resistance (ERAR) in the Greater Mekong Subregion, a high-level
plan of attack to contain the spread of drug-resistant parasites and to provide
life-saving tools for all populations at risk of malaria.
But even as this work was under way,
additional pockets of resistance emerged independently in new geographic areas
of the subregion.
In parallel,
there were reports of increased resistance to ACT partner drugs in some
settings. A new approach was needed to keep pace with the changing malaria
landscape.
Consequently, WHO’s Malaria Policy Advisory
Committee in September 2014 recommended adopting the goal of eliminating P.
falciparum malaria
in this subregion by 2030.
WHO launched the Strategy for Malaria
Elimination in the Greater Mekong Subregion (2015–2030) at the World Health
Assembly in May 2015, which was endorsed by all the countries in the subregion.
With technical guidance from WHO, all GMS
countries have developed national malaria elimination plans.
Together with partners, WHO will provide
ongoing support for country elimination efforts through a new malaria
elimination initiative that will replace the former ERAR hub.
Surveillance
Surveillance entails tracking of the disease
and programmatic responses, and taking action based on the data received.
Currently many countries with a high burden of
malaria have weak surveillance systems and are not in a position to assess
disease distribution and trends, making it difficult to optimize responses and
respond to outbreaks.
Effective surveillance is required at all
points on the path to malaria elimination and the Global Technical Strategy for
Malaria 2016-2030 (GTS) recommends that countries transform surveillance into a
core intervention.
Strong malaria surveillance enables programmes
to optimize their operations, by empowering programmes to:
- advocate for investment from domestic and
international sources, commensurate with the malaria disease burden in a
country or subnational area;
- allocate resources to populations most in
need and to interventions that are most effective, in order to achieve the
greatest possible public health impact;
- assess regularly whether plans are
progressing as expected or whether adjustments in the scale or combination of
interventions are required;
- account for the impact of funding received
and enable the public, their elected representatives and donors to determine if
they are obtaining value for money; and
- evaluate whether programme objectives have
been met and learn what works so that more efficient and effective programmes
can be designed.
Stronger malaria surveillance systems are
urgently needed to enable a timely and effective malaria response in endemic
regions, to prevent outbreaks and resurgences, to track progress, and to hold
governments and the global malaria community accountable.
Elimination
Malaria elimination is defined as the
interruption of local transmission of a specified malaria parasite species in a
defined geographical area as a result of deliberate activities.
Continued measures are required to prevent
re-establishment of transmission. (The certification of malaria elimination in
a country will require that local transmission is interrupted for all human
malaria parasites.)
Malaria eradication is defined as the
permanent reduction to zero of the worldwide incidence of malaria infection
caused by human malaria parasites as a result of deliberate activities.
Interventions are no longer required once eradication has been achieved.
The rate of progress in a particular country
will depend on the strength of its national health system, the level of
investment in malaria control, and a number of other factors, including:
biological determinants, the environment, and the social, demographic,
political, and economic realities of a particular country.
In countries with high or moderate rates of
malaria transmission, national malaria control programmes aim to maximize the
reduction of malaria cases and deaths.
As countries approach elimination, enhanced
surveillance systems can help ensure that every infection is detected, treated
and reported to a national malaria registry.
Patients diagnosed with malaria should be
treated promptly with effective antimalarial medicines for their own health and
to prevent onward transmission of the disease in the community.
Countries that have achieved at least 3
consecutive years of 0 local cases of malaria are eligible to apply for the WHO
certification of malaria elimination. In recent years, 7 countries have been
certified by the WHO Director-General as having eliminated malaria: United Arab
Emirates (2007), Morocco (2010), Turkmenistan (2010), Armenia (2011), Maldives
(2015), Sri Lanka (2016) and Kyrgyzstan (2016).
The WHO Framework for Malaria Elimination (2017)
provides a detailed set of tools and strategies for achieving and maintaining
elimination.
Vaccines against malaria
RTS,S/AS01 (RTS,S) – also known as Mosquirix –
is an injectable vaccine that provides partial protection against malaria in
young children.
The vaccine is being evaluated in sub-Saharan
Africa as a complementary malaria control tool that potentially could be added
to (and not replace) the core package of WHO-recommended preventive, diagnostic
and treatment measures.
In July 2015, the vaccine received a positive
opinion by the European Medicines Agency, a stringent medicines regulatory
authority.
In October 2015, two WHO advisory groups
recommended pilot implementation of RTS, S/AS01 in a limited number of African
countries.
WHO adopted these recommendations and is
strongly supportive of the need to proceed with the pilot programme as the next
step for the world’s first malaria vaccine.
In November 2016, WHO announced that the RTS,S
vaccine would be rolled out in pilot projects in 3 countries in sub-Saharan
Africa.
Funding is now secured for the initial phase
of the programme and vaccinations are due to begin in 2018.
These pilot projects could pave the way for
wider deployment of the vaccine if safety and effectiveness are considered
acceptable.
WHO response
The WHO Global Technical Strategy for Malaria
2016-2030 – adopted by the World Health Assembly in May 2015 – provides a
technical framework for all malaria-endemic countries.
It is intended to guide and support regional
and country programmes as they work towards malaria control and elimination.
The Strategy sets ambitious but achievable
global targets, including:
- Reducing malaria case incidence by at least
90% by 2030.
- Reducing malaria mortality rates by at least
90% by 2030.
- Eliminating malaria in at least 35 countries
by 2030.
- Preventing a resurgence of malaria in all
countries that are malaria-free.
This Strategy was the result of an extensive
consultative process that spanned 2 years and involved the participation of
more than 400 technical experts from 70 Member States.
It is based on 3 key pillars:
- ensuring universal access to malaria
prevention, diagnosis and treatment;
- accelerating efforts towards elimination and
attainment of malaria-free status; and
- transforming malaria surveillance into a
core intervention.
The WHO Global Malaria Programme (GMP)
coordinates WHO's global efforts to control and eliminate malaria by:
- setting, communicating and promoting the
adoption of evidence-based norms, standards, policies, technical strategies,
and guidelines;
keeping independent score of global progress;
- developing approaches for capacity building,
systems strengthening, and surveillance; and
- identifying threats to malaria control and
elimination as well as new areas for action.
GMP is supported and advised by the Malaria
Policy Advisory Committee (MPAC), a group of 15 global malaria experts
appointed following an open nomination process.
The MPAC, which meets twice yearly, provides
independent advice to WHO to develop policy recommendations for the control and
elimination of malaria.
The mandate of MPAC is to provide strategic
advice and technical input, and extends to all aspects of malaria control and
elimination, as part of a transparent, responsive and credible policy setting
process.
