The sensitivity of Plasmodium falciparum strains to chloroquine was tested in one locality in the north-east of the United Republic of Tanzania, where a chloroquine-medicated salt project has been implemented for chemosuppression for many years, and where large amounts of the drug have been available during the last decade for the treatment of malaria infections.Single doses of chloroquine (5 or 10 mg of base/kg of body weight) failed to clear P. falciparum trophozoites in asymptomatic parasite carriers selected from the school population. In comparison, clearance had been obtained easily ten years previously with 5 mg of base/kg of body weight in several localities in the area.A total dose of 25 mg of base/kg of body weight given over a 3-day period succeeded in clearing asexual parasites from the peripheral blood by day 3 in all instances. Asexual parasites were not found again during the nine days following administration of the drug.All the schoolchildren who had received 5 or 10 mg of base/kg of body weight at the beginning of the trial were treated with a further 20 mg of base/kg of body weight at the end of the 7-day observation period. Asexual parasites reappeared in the blood of some of these children 7-10 days after the second administration of the drug.Using the in vitro microtechnique, incomplete schizont inhibition was observed in 3 out of 21 cases at a chloroquine concentration of 1.14 mumol/litre of blood, which is the discriminating dosage for resistance at RI level.No cases of retinopathy related to the prolonged use of chloroquine were detected among the 221 residents who had spent more than 16 consecutive years in the locality.

Decreased sensitivity and incipient resistance of Plasmodium falciparum strains to chloroquine have been reported from Mto-wa-Mbu, in the north-east of the United Republic of Tanzania. In this locality the population had been exposed to chloroquine pressure for about two decades, in the form of medicated salt and through easy availability of the drug itself. In an attempt to find out whether such chemosuppression had influenced the immune response of the population, two seroepidemiological surveys were carried out in March 1981 and March 1982; the second survey was performed to confirm the results obtained in the first one. The humoral immunological response was measured by the immunofluorescent antibody technique. In the absence of information on the immunological profile that existed in the area prior to the introduction of chloroquine in 1960, the results of the present surveys were compared with those obtained in another locality in the north-east of the United Republic of Tanzania in 1967, and in the West Kiang district of Gambia in 1965. The two areas used for comparison exhibited a malaria endemicity similar to that prevailing in Mto-wa-Mbu prior to the introduction of the medicated salt. The results from Mto-wa-Mbu showed a significantly lower proportion of subjects with positive titres and a lower geometric mean titre in all age groups.A reduction in the humoral immunological response might be explained by the drug pressure that has been exerted in the area for many years. The depressed immune response found at Mto-wa-Mbu, however, was so marked that other factors may have contributed to its establishment.In view of the importance of these findings, it is recommended that further, longitudinal serological studies be conducted in the field to assess the effects of chemosuppression on the immune response of the protected populations.

The entomological inoculation rate is presented as a comprehensive indicator of malaria transmission level, its relative changes reflecting the risk of potential epidemic development. This rate is a known function of several epidemiological direct factors and is particularly sensitive to the survival rate and the sporogonic cycle of the vector. Although not yet fully quantifiable, relationships exist between direct factors responsible for the transmission of infection and certain meteorological and environmental indirect factors like air temperature, relative humidity, or importation of malaria parasites.The establishment of a two-stage monitoring system is suggested: the first stage would involve setting up a warning system based on the surveillance of the relevant indirect factors; at the appropriate time, this would trigger the second stage monitoring of the epidemiological direct factors having a definite bearing on the development of malaria outbreaks. It is recognized that the gain in reliability of the proposed approach depends largely on the progress still to be achieved in the quantification of the complex system of relations connecting the main direct factors with single or combined indirect factors. It is also noted that the proposed monitoring system should, in due course, provide the decision-makers with the epidemiological information required for the selection and implementation of intervention measures designed to prevent epidemic resurgences.

In 1978, public health authorities, by means of large-scale control operations, succeeded in containing a severe malaria epidemic that had reached alarming proportions in the Cukurova and Amikova plains of southern Turkey. The benefits derived from this intervention are indirectly quantified in this article by estimating the number of cases that would have ocurred in the area if remedial measures had not been applied.For this purpose a simple mathematical model was fitted to both the number of cases in January (seasonal minimum) and the number of cases in July/August (seasonal maximum) that were recorded during the years 1976, 1977, and the beginning of 1978; the incidence trend from 1978 onwards was then determined by projection. By this method, it was possible to estimate that in the absence of intervention the projected annual parasite incidence would have been 75.4 per 1000 in 1978 instead of the observed incidence of 24.5 per 1000. According to the forecast, this incidence would have reached 100.9 per 1000 in 1979, 115.1 per 1000 in 1980, to arrive at a final stable level of 129.4 per 1000, if intervention measures had not been applied.Comparison of the number of malaria cases actually detected in 1978 (70 468) with the number projected in the absence of intervention (226 252) seems to indicate that about 2/3 of the expected cases were prevented in 1978 by the remedial measures applied.

This paper is an attempt to relate modifications observed in general and infant mortality rates with the dynamic changes in transmission induced by malaria control measures. The observations indicated relationships between the efficacy of control and a decrease in mortality. The daily parasitological inoculation rate was reduced from 0.00958 infective bites per individual before treatment to 0.00037 after treatment (a decrease of 96%). In two years, general mortality decreased from 23.9 to 13.5 deaths per 1000 population and infant mortality decreased from 157 to 93 per 1000 live births. This indirect benefit of malaria control deserves attention in a wider assessment of measures directed against vector-borne diseases.

Au cours d'une etude longitudinale qui s'est diroulke d'avril 1970 a octobre 1972 (6 enquetes faites a des intervalles de 6 mois), un total de 13 044 personnes habitant 18 localites situe'es dans 8 Gouvernorats de Tunisie ont ete soumises a des examens parasitologiques visant a etablir la presence de parasites du paludisme dans le sang peripehrique, ainsi qu'a des examens se'rologiques pour la recherche des anticorps par la methode d'immunofluorescence au moyen de l'antige'ne heterologue Plasmodium cynomolgi bastianellii. Les re'sultats ont ete e'value's et analyse's en fonction de la situation eJpide6mio-logique passe'e et pre'sente en Tunisie. Le tableau qui en resulte est celui du paludisme en voie de disparition en l'absence de nouvelles infections. Il a ete' montrJ que la mdthode serologique employe'e complete bien les e'valuations e6pid6miologiques et serait particulierement utile dans les ope'rations antipaludiques, lorsque l'indice plasmodique est devenu trop bas pour que les e'valuations classiques par enquete syste6matique dans les secteurs temoins donnent des re'sultats significatifs. En outre cette mithode pourrait etre appliquee a des enquetes sur d'autres maladies parasitaires.