Malaria N° 3 - Subject N° 1

LOW BIRTH WEIGHT, PLACENTAL INFECTION, AND SEASONAL VARIATION OF MALARIA TRANSMISSION IN BOBO-DIOULASSO (BURKINA FASO)
J-F. Molez, M-F. Bosseno & S-G. Traoré

SUMMARY
The proportion of newborns with low birth weight (less than 2500 g.) is one indication of the progress of health strategies in devoloping countries. Low weight can be due to numerous factors, in particular malaria infection which badly affects foetal development (risk factor on outcome of pregnancy, miscarriage, low birthweight and pre-term delivery). Placental infection is indirectly responsible for low birth weight, parasitemia develops particularly in intervillous spaces, causing haemodynamic troubles, foetal hypoxia (especially when the placenta is highly infected), and reducing intra-uterine growth. In two maternity in Bobo-Dioulasso (Burkina Faso), the frequency of low birth rates is 10 % for male newborns and 20 % for female newborns. A study of the mother/child couple and placental parasitemia was carried out, and a placental infection rate of 10 % (yearly average) was found in pregnant women. However, no significant difference was found between the frequency of low birth weight in newborns from healthy placentas and those infected with Plasmodium falciparum, in data covering 12 months of the year.

In this region of Burkina Faso the malaria transmission is continuous, but endemic malaria follows a seasonal variation. The seasonal frequency of malaria attacks varies with the rainy season, placental malaria infections vary in the same way (from 24,5 % at the end of the rainy season to 1 % at the end of the dry season) as well as intervillous spaces in the placental section highly charged with parasites. By separating into two periods our observations on low birth weight, taking into account the dynamics of transmission, we found a seasonal effect of placental infection on low weight. Thus we found low birth weight in infant from infected placentas born during the dry season (foetal growth occured during the rainy season which is the period of high malaria transmission). However, infants who where born during the rainy season from infected placenta (pregnancy took place during the dry season which is the period of minimum transmission) showed no significant difference in weight with that of the average newborn. Our survey thus shows a particular period during which low birth weight was observed in newborns from placentas infected with Plasmodium falciparum (less 300 g. on average for both sexes : less 120 g. for boys and less 420 g. for girls). Thus in Bobo-Dioulasso, in the ecological situation of guineo-sudanian area, there is a direct relationship between the seasonal variation in malaria transmission rate and low birth weight observed in newborns. However, the responsibility of malaria infection in low birth weight should be weighed up in terms of dynamics of malaria transmission. So in regions where malaria transmission is continuous and more intense, placental infection, despite the fact that it affects foetal weight, is not a serious problem. The impact of placental malaria infection on birth weight is all the more important in endemic areas with variations in the transmission rate. In malaria endemic areas of Africa, young women primi- or second-gravidae are particularly affected by placental infection, this additional factor to the already high obstetrical risk means that these pregnancies should be closely followed up in antenatal clinics.

KEY-WORDS: Low birth weight, Malaria, Plasmodium falciparum, Placental infection, Seasonal variation of malaria transmission, Burkina Faso