History and exam
Key diagnostic factors
common
presence of risk factors for acquiring malaria
Key risk factors include travel to an endemic area (especially visiting friends and relatives), inadequate or absent chemoprophylaxis, and non-use of an insecticide-treated bed net in an endemic area.
presence of risk factors for severe disease
Low host immunity: patients who did not grow up in an endemic area or who have not had previous malaria are more likely to have severe disease.
Pregnancy: all types of malaria increase the risk of miscarriage. Pregnancy leads to higher percentage parasitaemia and anaemia in Plasmodium falciparum infection.
Age <5 years: children are less likely than adults to complain of chills, myalgia, or headaches, and more likely to present with non-specific symptoms.
Immunocompromise: people with comorbidities, including HIV infection, are susceptible to developing severe malaria infection.
Older adults: susceptible to severe disease, particularly due to subtle immunodeficiency associated with ageing.
fever or history of fever
Fever, or history of fever, is universal. Characteristic paroxysms of chills and rigors followed by fever and sweats may be described. Usually with an associated tachycardia.
Patterns of fever are rarely diagnostic at presentation but may develop over time: fevers occurring at regular intervals of 48 hours may be associated with Plasmodium vivax or Plasmodium ovale infection, and at intervals of 72 hours with Plasmodium malariae infection. In most patients there is no specific fever pattern.
Other diagnostic factors
common
headache
Non-specific but common complaint.
weakness
Non-specific but common complaint.
myalgia
Non-specific but common complaint.
arthralgia
Non-specific but common complaint.
anorexia
Non-specific symptom.
diarrhoea
Non-specific symptom.
uncommon
seizures
Suggests falciparum infection, which is the most common cause of cerebral malaria. However, febrile illnesses reduce seizure threshold in known epileptic patients. Seizures may be related to hypoglycaemia (a complication of quinine treatment).
nausea and vomiting
Non-specific symptom.
abdominal pain
Non-specific symptom.
pallor
Anaemia is often present.
hepatosplenomegaly
Common presenting sign, although not common at time of initial presentation in returning travellers.
jaundice
Suggests falciparum infection, which is the most common cause of severe disease.
altered level of consciousness
Suggests falciparum infection, which is the most common cause of severe disease. However, any febrile illness can cause confusion in an older patient. Patients with cerebral malaria may have bruxism and retinal changes (haemorrhages and retinal whitening).
hypotension
Suggests falciparum infection, which is the most common cause of severe disease. Circulatory shock may indicate concurrent bacterial sepsis.
bleeding
Bleeding complications are rare. Significant bleeding (e.g., recurrent or prolonged bleeding from gums, nose, or venepuncture sites; haematemesis; melaena) suggests falciparum infection, which is the most common cause of severe disease. It may also suggest disseminated intravascular coagulation, associated with other causes of sepsis.
anuria/oliguria
Suggests falciparum infection, which is the most common cause of severe disease.
tachypnoea
May indicate severe malaria with acidosis.
Risk factors
strong
travel to endemic area
Each year, 25 million to 30 million people from the US and Europe travel to the tropics, of whom approximately 10,000-30,000 acquire malaria.[18]
People (and their families) who return from travel to an endemic area of origin (especially those visiting friends and relatives) constitutes two-thirds of all imported malaria, with most patients not taking malaria chemoprophylaxis.[32] This may be due to a number of reasons: if they grew up not taking prophylaxis, they may not see it as important or may not consider it; they may take incorrect prophylaxis; they may perceive the risk as low, especially if only visiting a major city.
inadequate or absent chemoprophylaxis
The incidence of Plasmodium falciparum malaria in travellers who do not take prophylactic drugs is highest in West Africa (52 cases/1000 years exposed).[33] In South America, India, and Pakistan, a low risk of 1 case per 2000-3000 years exposed exists.[34][35] Chemoprophylaxis significantly reduces mortality rates.[36]
insecticide-treated bed net not used in endemic area
Pyrethroid-treated mosquito nets are recommended for travellers to certain endemic areas where mosquitoes rest indoors and bite at night (e.g., Africa), to reduce risk of mosquito bites.
low host immunity (severe disease)
People who have little or no immunity (i.e., individuals living in non-endemic or low-transmission areas) are most at risk for disease and developing serious illness.[16]
pregnancy (severe disease)
Pregnant women remain one of the most susceptible patient groups to disease in endemic areas. Pregnant women infected with Plasmodium falciparum are susceptible to complications of pregnancy (e.g., pregnancy loss, preterm delivery, low birth weight, maternal anaemia). In addition, the prevalence of Plasmodium vivax infection and parasite density increases during pregnancy, due to the reticulocytosis of pregnancy (P vivax exclusively invades reticulocytes).[30][37]
age <5 years (severe disease)
Children aged <5 years remain one of the most susceptible patient groups to disease in endemic areas. They are more likely to have symptomatic infection and complications of malaria.[38]
immunocompromise (severe disease)
Individuals with comorbidities, including HIV infection, are more susceptible to developing severe malaria.
older age (severe disease)
malnutrition (severe disease)
Children aged <5 years with acute malnutrition presenting with uncomplicated falciparum malaria were at higher risk of delayed parasite clearance, treatment failure, and reinfection.[31]
weak
iron administration (children)
While iron administration to prevent anaemia in children living in endemic areas has been claimed to increase the risk of malaria (or severe malaria), one Cochrane review found that iron treatment does not increase the risk of clinical malaria when regular malaria prevention or management services are in place.[42][43]
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