training module for medical officers primary health centre - NVBDCP

SESSION – 2: MALARIOLOGY2.1: EPIDEMIOLOGY OF MALARIAEpidemiological factorsAgent factors (Parasite – Plasmodium) Three species prevalent in India P.vivax is the predominant species in India : 50 - 55% P.falciparum contributes about 40 - 45% of malaria cases P.malariae contributes less than 1% of malaria cases in India Sporogony longest in P.malariae and shortest in P.vivax. No relapses in P.falciparum and P.malariae Different strains of P.vivax show different relapsing patternsHost factorsAge: Parasitaemia in infancy, low initially and increases as maternally acquired immunitydecreases.Sex: No influence on susceptibility or parasite densityPregnancy: Primigravidae have higher parasitaemia with P.falciparum and are at greater riskthan multiparaeGenetic factorso HbF and Thalassaemia seem to protect against malaria infectiono Sickle cell trait: Relative protection against P. falciparum infectionHuman immune mechanismo Repeated exposure leads to immunityo Immunity is slow to develop but continues as long as parasitaemia is presento Immunity declines when the parasitaemia is cleared (naturally or by therapy) and usuallydisappears in 2 to 3 yearso Immunity is species and strain specifico Immunity restricts production of gametocyteso Immunity diminishes fertilization in vectoro Children have variable experience with malaria and are likely to suffer more.Environmental factorsClimate influences density, longevity and behaviour of vectors and duration of sporogonyRainfall influences the number of breeding places and their characteristicsType of soil, terrain and contours determine run-off rate of rain water and percolation into subsoilstratumRole of impounding reservoirs, irrigation canals and seepage of water from canalsHigh temperature and humidity:o Lower survival of mosquitoeso Affect blood meal frequencyo Affect sporogony8