ABSTRACT
During a longitudinal survey done in the degraded forest area south of Brazzaville (People's Republic of the Congo), it appeared that plasmodic index of preschool children was always lower than 50% in spite of an inoculation rate of about one infected bite per child per night all along the year. The actual incidence rate estimated with Muench model was h = 0,015 while the recovery rate was r = 0,032 (i.e. about three times faster than the usual values admitted since Mac Donald work) for young children (0 to 4 years old). A computer study has shown that an incidence of h1 = 0,0012 was enough for the "infection" of children (Ross model) while an incidence of h2 = 0,0014 would induce a situation of superinfection (Dietz et al. model). Therefore the actual incidence was 10 to 12 times higher than the critical values of the incidence rate. To decrease the malaria transmission at a level lower than the critical values i.e. to obtain a reproduction rate below I the calculations and graphs have shown that anopheline density or human gametocytaemia have to be reduced by about 90% while the survival rate of the vectors must be reduced by about 12%. Therefore it appeared that the determination of the critical levels of every parameters of malaria transmission is a needful stage for a better planification of any malaria control programme.
Subject(s)
Malaria/transmission , Age Factors , Animals , Anopheles/parasitology , Child, Preschool , Congo , Female , Humans , Infant , Infant, Newborn , Longitudinal Studies , Malaria/epidemiology , Malaria/prevention & control , Mathematics , Mosquito ControlABSTRACT
The relationship between sickle cell trait and falciparum malaria was studied in the village of Djoumouna, twenty kilometers south west of Brazzaville. Malaria is characterized by a stable high intensity of transmission on the average one infective mosquito bite by night and by child contrasting with a relatively low malarial infection rate. The prevalence of carriers of an S gene (AS) does not change with age: 22.2% for children under 5 years, 22.1% for childrern between 5 and 15 years, and 22.9% in adults. Malarial infection rates are 32% in homozygous AA children under five years and 38% in AS children, an insignificant difference. Our data for this region of the Congo fail to confirm the hypothesis that the AS genotype protects the carrier against Plasmodium falciparum infection.
Subject(s)
Anemia, Sickle Cell/genetics , Malaria/epidemiology , Malaria/genetics , Sickle Cell Trait/genetics , Adolescent , Adult , Child , Child, Preschool , Congo , Female , Genotype , Humans , Infant , Male , Plasmodium falciparumABSTRACT
The authors have elaborated a formula to calculate the average number of times an anopheline parous female bites in one day ("L") according to its gonotrophic cycle and more specially to its behaviour before and after oviposition (parameters "alpha" and "A". The formula was applied to Anopheles gambiae observed at Djoumouna village (L = 0.40) and to Anopheles nili observed at M'Pola village (L = 0.30). The value obtained has then to be multiplied by the anthropophilic index to obtain the "a" parameter of MacDonald (1957) when studying malaria transmission in a village. On the other hand such a formula allowed a better evaluation of biting frequency of a vector, thus of risks of transmission of diseases, according to the respective situation of human houses and water storages. An important point which ahs to be born in mind when planning artificial permanent reservoirs.
