A-Textbook-of-Clinical-Pharmacology-and-Therapeutics-5th-edition

CHAPTER 47
MALARIA AND OTHER
PARASITIC INFECTIONS
● Malaria 361
● Trypanosomal infection 364
● Helminthic infection 364
MALARIA
It estimated that malaria infects 300–500 million humans per
year throughout the world, and up to 2 million (mainly children)
die annually. Approximately 40% of the world population
live in malarious areas, particularly in equatorial regions.
Malaria is transmitted to humans in the saliva of the anopheles
mosquito and is caused by protozoan organisms of
the genus Plasmodium. There are four major species, namely
P. falciparum, P. vivax, P. ovale and P. malariae. P. falciparum is
the most lethal form. Malaria is one of the most common
causes of serious illness in the returning traveller. At least
2000 cases are imported into the UK (10 000 in Europe) per
year. Air travel and the incubation period of the disease
have raised the awareness of diagnosing and appropriately
treating malaria even in areas where it is not endemic (e.g.
hospitals near international airports in Western Europe and
the USA).
Visitors to endemic areas must be warned of the infection
risk and advised that prophylactic drug therapy should be
taken, but that it is not 100% effective. They should also be
advised to wear long-sleeved clothing to cover extremities
(especially in the evenings, when mosquitos feed) to use
mosquito-repellent sprays, to sleep in properly screened rooms
with mosquito nets (impregnated with pyrethroids) around the
bed and/or to burn and vapourize synthetic pyrethroids during
the night. In addition to chemoprophylactic drug therapy,
travellers to remote areas should be advised to carry standby
antimalarial drug treatment with quinine. Where there is doubt
concerning the suitability of drug therapy for malaria prophylaxis
or treatment, the malaria reference laboratory at the
London School of Hygiene and Tropical Medicine has advice
and guidance (Tel. 020 7636 3924 for health professionals and
Tel. 09065 508908 for the general public, regarding malaria
prophylaxis: website www.hpa.org.uk/srmd/malaria).
Figure 47.1 illustrates the Plasmodium life cycle and the
therapeutic targets.
Female
anopheline
mosquito
Sporozoites
(in salivary gland)
BITE
Human
Hepatic
Pre-erythrocyte
phase
ve
Drug therapy
Suppressive
(quinacrine,
pyrimethamine)
Oocyst
Erythrocytic
stages
Schizogony
Schizonts
Merozoites
ve
Clinical cure
(chloroquine,
quinine,
amodiaquine,
pyrimethamine,
mefloquine,
halofantrine)
Radical cure
(primaquine)
Zygote
Trophozoites
ve
ve
Atovaquone
Artemesinin
Microgamete
and
macrogamete
BITE
Microgametocyte
and
macrogametocyte
ve
Gametocidal
(pyrimethamine)
Figure 47.1: Malaria
life cycle and type of
drug treatment.