Malaria - Parasitology

Malaria

·        Transmitted by mosquito and very rarely transfusion

Clinical

·        Irregular fever – peaks on release of parasite from infected RBCs. May only be mild if person has immunity (ie previous exposure). Various strains have various periodicities

·        Chills

·        Headache

·        Malaise

·        Vomiting (20%)

·        Diarrhoea (<5%)

·        ie similar to Typhoid

History

·        Travelled to a malaria country

·        What conditions did you stay in, rural/urban, etc

·        Was chemoprophylaxis taken, how was compliance

·        Diagnosed overseas

·        When did you return to NZ (Plasmodium Falciparum usually in 1 month, P Vivax up to a year)

·        Length of illness

Diagnosis

·        Blood film for plasmodium protozoa: a thick film is necessary as well as the standard thin film if parasites are scant (eg if have some immunity)

·        Pointless if patient is afebrile

·        If initially negative, repeat 12 hourly for 48 hours

·        Critical that you find out which plasmodium species is present, eg:

o   Plasmodium Falciparum: common in Africa, can cause cerebral malaria (fatal)

o   Plasmodium Vivax: more common in Asia/Oceania

·        Features of poor prognosis:

o   CNS signs: disturbed consciousness, repeated convulsions

o   Respiratory distress

o   Haemorrhage, shock 

o   Biochemical markers: ­Cr, ¯HCO₃, ­bilirubin, ¯glucose

o   High parasitic load

Prevention

·        Assessment of risk: 

o   Malaria geography: transmission rates vary by country (eg high in Sub-Sahara, PNG, Solomon Islands)

o   Likely extent of contact with mosquitoes (eg standard of accommodation)

·        Anti-mosquito measures: long sleeves & trousers, insect repellent/sprays, nets

·        Chemoprophylaxis:

o   Start 1 week beforehand and continue till 4 weeks after leaving

o   Mefloquine (effective against chloroquine resistant P Falciparum).

§  250 mg weekly

§  Side effects: nausea, diarrhoea, dizziness – usually self-limiting.

§  At higher doses (eg for treatment) convulsions and sinus bradycardia 

§  Contraindications: drugs altering cardiac conduction, psychiatric disease, epilepsy, pregnant, kids < 5kg, or where fine CNS co-ordination required (eg airline pilots)

o   Doxycycline, 100 mg daily

§  After food otherwise gastritis

§  In rural areas of SE Asia, where mefloquine-resistant strains of P falciparum are reported

§  Contraindicated in pregnancy women and children 

o   Chloroquine + proguanil: Only one safe for first trimester. Low efficacy against drug resistant falciparum

·        Chloroquine weekly – countries without chloroquine-resistant P falciparum (Central America north of Panama)

Treatment

·        P Vivax, P Ovale, P Malariae:

o  Acute treatment: 3 days of Chloroquine

o  For radical cure in P Vivax or P Ovale:

§  Primaquine for 2 weeks (screen for G6PD deficiency first)

§  Eradicates exo-erythrocytic liver cycle.  If you don‟t, they will relapse 

o  Relapse common (20%) – maybe several months later. If so, repeat 3 days of Chloroquine followed by 2 weeks of higher dose of Primaquine

·        P Falciparum:

o  Quinine sulphate + Doxycycline for 7 days

o  No persisting cycle so relapse not a problem

o  Cerebral malaria: iv quinine: loading dose then maintenance infusion

·        Drug resistance:

o  Chloroquine-resistant strains of plasmodium falciparum are widespread

o  Chloroquine-resistant strains of P Vivax reported in Indonesia and PNG