Summary of Malaria & Antimalarial therapy

Abdul Waris KhanSoepel: 12Internal medicine

Malaria

• Human malaria is usually caused by one of four species of the genus Plasmodium:

– P. falciparum

– P. vivax

– P. ovale

– P. malariae

• Malaria probably originated from animal malarias in Central Africa, but was spread around the globe by human migration.

• Public health measures and changes in land use have eradicated malaria in most developed countries.

Epidemiology

• Some 400 million people are infected every year and over 1 million die annually.

• 25 000 international travellers per year are infected.

• Australia, the USA and most of the Mediterranean are malaria-free.

• Mortality is still mainly seen in infants, but older children and adults may develop chronic ill health due to repeated infections.

• Malaria is transmitted by the bite of female anopheline mosquitoes.

• The parasite undergoes a temperature-dependent cycle of development in the gut of the insect.

Pathogenesis

• The pathology of malaria is related to anaemia, cytokine release and in the case of P. falciparum, widespread organ damage due to impaired microcirculation.

• The anaemia seen in malaria is multifactorial. In P. falciparum malaria, red cells containing schizonts adhere to the lining of capillaries in the brain, kidneys, gut, liver and other organs.

• As well as causing mechanical obstruction these schizontsrupture, releasing toxins and stimulating further cytokine release.

Clinical features

• Typical malaria is seen in non-immune individuals.

• The normal incubation period is 10–21 days, but can be• longer.

• The most common symptom is fever, although• malaria may present initially with general malaise,

headache,• vomiting, or diarrhoea.

• The temperature often reaches 41°C and is accompanied by rigors and drenching sweats.

P. vivax or P. ovale infection

• The illness is usually relatively mild (although P. vivax can occasionally cause severe disease).

• Anaemia develops slowly and there may be tenderhepatosplenomegaly.

• Spontaneous recovery usually occurs within 2–6 weeks, but hypnozoites in the liver can cause relapses for many years after infection.

• Repeated infections often cause chronic ill health due to anaemia and hyperreactive splenomegaly.

P. malariae infection

• This also causes a relatively mild illness, but tends to run a more chronic course.

• Parasitaemia may persist for years, with or without symptoms.

• In children, P. malariae infection is associated with glomerulonephritis and nephroticsyndrome.

P. falciparum infection

• This causes, in many cases, a self-limiting illness similar to the other types of malaria, although the paroxysms of fever are usually less marked.

• However, it may also cause serious complications and the vast majority of malaria deaths are due to P. falciparum.

• Patients can deteriorate rapidly and children in particular progress from reasonable health to coma and death within hours.

• A high parasitaemia (>1% of red cells infected) is an indicator of severe disease.

• Cerebral malaria is marked by diminished consciousness, confusion and convulsions, often progressing to coma and death.

• Blackwater fever is due to widespread intravascular haemolysis, affecting both parasitized and unparasitized red cells, giving rise to dark urine.

Diagnosis

• Malaria should be considered in the differential diagnosis of anyone who presents with a febrile illness or having recently left, a malarious area.

• Falciparum malaria is unlikely to present more than 3 months after exposure, even if the patient has been taking prophylaxis, but vivaxmalaria may cause symptoms for the first time up to a year after leaving a malarious area.

• Diagnosis is usually made by identifying parasites on a Giemsa-stained thick or thin blood film

• At least three films should be examined before malaria is declared unlikely.

Treatment of uncomplicated malaria.

• The drug of choice for susceptible parasites is chloroquine.

• P. vivax, P. ovale and P. malariae are usually sensitive to this drug.

• Following successful treatment of P. vivax or P. ovale malaria, it is necessary to give a 2- to 3-week course of primaquine (15 mg daily) to eradicate the hepatic hypnozoites and prevent relapse.

• The artemisinin-based drugs are the most effective treatment for both uncomplicated and severe infections with P. falciparum, in adults and in children.

• Artemisinin-based combination therapy (ACT) is the recommended oral treatment for uncomplicated falciparum malaria worldwide.

• Artemisinin should not be given as monotherapy to limit resistance.

• The WHO recommends that a single dose of primaquine should be given as a gametocide, to decrease transmission.

Treatment of severe falciparum malaria

• Severe malaria, indicated by the presence of the complications, or a parasite count above 1% in a nonimmune patient, is a medical emergency.

• Intravenous artesunate is more effective than intravenous quinine and should be used where available.

• Absorption from intramuscular injection is less reliable than from intravenous injection.

• Intensive care facilities may be needed, including mechanical ventilation and dialysis.

• Severe anaemia may require transfusion.

Prevention and control

• Mosquito eradication is usually achieved either by the use of insecticides, house spraying with DDT or by manipulation of the habitat (e.g. marsh drainage).

• Non-immune travellers to malarious areas should take measures to avoid insect bites, such as using insect repellent (diethyltoluamide, DEET, 20–50% in lotions and sprays) and sleeping under mosquito nets.

• Antimalarial prophylaxis should also be taken in most cases, although they are not 100% effective.

References

• Kumar and Clark’s clinical medicine 8th edition