Evaluation of fenitrothion for the control of malaria.

Fenitrothion was evaluated for residual spraying in antimalaria programmes in a large-scale field trial near Kisumu, Kenya from 1972 to 1976. The insecticide was applied in a hyper/holoendemic malarious area of 200 km(2) inhabited by about 50 000 people. All houses and animal shelters were sprayed at a target dosage rate of 2 g/m(2) at 3-month intervals for a total of 8 consecutive spray rounds in 2 years. The malaria vectors Anopheles gambiae species A and B and A. funestus were reduced to negligible densities indoors and outdoors immediately after initiation of spraying and for 10 months after the last spray round. However, A. gambiae reappeared during the main wet season at densities high enough to reestablish low-level transmission for short periods. Spraying produced a marked and rapid decrease in both the incidence and prevalence of malaria. The daily probability of acquiring malaria infection was reduced from 0.009 before spraying to 0.0003 under spray protection, a reduction of 96%. Data collected on a longitudinal basis indicated that sustained spray protection would reduce malaria prevalence to an asymptotic limit of 6.9% under the assumption that the inoculation and recovery rates remain stable. However, to attain malaria eradication in this type of epidemiological situation, complementary measures such as mass drug administration appear to be necessary.

[The concept of risk in parasitic diseases with special reference to malaria (author's transl)]. / La notion de risque dans les maladies parasitaires avec référence particulière au paludisme

The concept of risk, its components and their interrelationship are described. Emphasis has been placed on the value of the variables to be taken into account in the selection of intervention measures: -- for the mosquito: the daily frequency of blood meals taken from man, the duration of the sporogonic cycle, the daily survival rate and the proportion of people with gametocytes in the peripheral blood; -- for man: the number of anophelines feeding on man in a unit of time, the proportion of mosquitoes with sporozoïtes in their salivary glands and the proportion of sporozoïtes able to infect man. Using these variables, it is possible to calculate the various risks incurred both by man and vector. Whenever possible and in order to be of greater value, the interventions should be directed against the variable which have the highest power. However, in view of the complexity of relations, it is better to construct a mathematical model able to simulate with the use of a computer, real epidemiological situations. A model has been recently developed for the study of the malaria dynamics and for the comparative evaluation of various methods of control.

A simple epidemiological model for evaluating the malaria inoculation rate and the risk of infection in infants.

A simple epidemiological model for evaluating the malaria inoculation rate and the risk of infection in infants was applied to describe the disease picture in an area of East Africa. Fairly good agreement was noted between the actual and expected curves of disease acquisition; this model could therefore be used for simulating epidemiological processes. Entomological and parasitological inoculation rates were compared by means of different approaches. As a result, it was possible to calculate the factor of proportionality defined as the proportion of anophelines having in their glands sporozoites that are actually infective.