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Several studies recently done in Africa south of the Sahara have clearly demonstrated that pyrethroid impregnated bednets should actually reduce malaria inoculation rate due to Anopheles gambiae and therefore high Plasmodium falciparum parasitaemia and malaria morbidity, even mortality. Nevertheless some concerns were recently raised on an eventual shift in the usual behavior of this species induced by the presence inside the house of bednets treated with pyrethroid insecticide known to have a deterrent or excito-repellent effect, and which could therefore lead to a biting behavior earlier than usual. The current limited study, done in Djoumouna, a place well known for the very high density of An. gambiae, has shown that the temporary presence inside a house of a bednet impregnated with deltamethrin (12.5 or 25 ma a.i./m2) has not induced any shift in the biting cycle of this species, but it actually reduced by some 50% its biting rate noticed on human beings. It is worth underlining that all sporozoite infected specimens were actually caught after midnight. This biting behavior of An. gambiae could explain why impregnated bednets are so efficient in reducing man-vector contact and malaria transmission.

Lutzomyia trapidoi, the more abundant anthropophilic species, is a presumed leishmaniasis vector in the Pacific foothills of Ecuador. Three biotopes have been sampled (dwelling, and nearby coffee crop and primary forest) in the focus of Paraiso Escondido, by human bait catches, from August 1991 to October 1992. A large number of sandflies, 6,965 specimens, have been dissected to estimate peri and hypopyloric infections. All the peripyloric infections, characterized by isoenzyme electrophoresis, were Leishmania panamensis. The percentage of these infections was low, around 3%, but they were massive. They occurred only in dry season. Hypopyloric infections were observed in Lu. trapidoi all the year round in the three biotopes. Their percentage was high, reaching 40%. Despite of many trials to cultivate the parasite on NNN medium, no stain could be isolated. It is suggested that the parasite could be L. equatorensis.

The Zumba focus of tegumentary leishmaniasis lies in the southwards Amazonian region of Ecuador. A clinico-epidemiological study has been carried out in the area on 83 patients attending health centers. All the biotopes suitable for sandflies, including dwellings, have been sampled from February to September 1992 by light trap and human bait catches. The number of sandflies caught amounts to 2,547. Anthropophilic sandfly fauna is poor and only three species have been recorded. Lutzomyia serrana abounds inside dwellings where it bites men even during daytime. The parasite was identified as an intermediate form between Leishmania panamensis and L. braziliensis. It will be described elsewhere. The high proportion of facial lesions suggests a domiciliary transmission for which Lu. serrana could be a good vector candidate.

In two leishmaniasis endemic foci of the Pacific coast of Ecuador, where the primary forest is severely attacked by human settlements, intradomiciliary sandfly catches, with light trap and human bait, have been carried out from August 1991 to October 1992. The presumed vector Lutzomyia trapidoi was by far the dominant species inside dwellings at Paraiso Escondido in the preandean hills (86% of the anthropophilic sandfly population, and 8.5 females/night catch by light trap). Not a single Lu. gomezi was caught in this village. At La Tablada, Lu. gomezi was the dominant anthropophilic species in the coastal cordillera (83% of anthropophilic sandfly population and 3.7 females/night catch by light trap); Lu. trapidoi accounted only for 4.6% of the total catches in this village. On human bait, catches were variable depending on the day and on the season, but dominant species were always the same. The percentage of Lu. trapidoi was higher on human bait than in light trap. Blood meal identifications of engorged Lu. gomezi and Lu. trapidoi confirmed the anthropophily of these two species in the houses.

We have evaluated the impact of anthropization of the forest on the incidence of leishmaniasis, due to Leishmania panamensis, in three coastal study areas, Corriente Grande (primary forest), Paraiso Escondido and La Tablada (secondary forest). The situation of isolated dwellings, in deforested areas, has also been analysed in the last two stations. In each station, the study of the density of anthropophilic sand flies, specially Lutzomyia trapidoi, has been conducted in the domestic environment, coffee plantations and undergrowth. The incidence of leishmaniasis was nearly non existent in primary forest, though it ranged from 106 to 147% in the more or less cleared forest. At Corriente Grande, none Lu. trapidoi was caught in houses. In the undergrowth, catches were low (8% of the total). At Paraiso Escondido, Lu. trapidoi was the dominant species, with more than 83% of the catches in the undergrowth and in the coffee plantations (41 Man/hour), as well as in dwellings (10.6 M/h). At La Tablada, in the domestic environment, Lu. gomezi, was the dominant species: 2.8 M/h against 0.1 M/h for Lu. trapidoi. In the coffee plantations and in the undergrowth Lu. trapidoi was the main species, 21 M/h and 14 M/h. Thus in the primary rainforest, leishmaniasis transmission can be very low. In disturbed forest, coffee plantations near houses are good biotopes for Lu. trapidoi. The cycle of L. panamensis has been adapted to this new ecological situation, by being closer to the houses. The reservoirs live and circulate throughout coffee plantations. In deforested areas, neither aggressive sand flies have been observed, nor leishmaniasis transmission.

The long-term efficacy of a single dose of ivermectin (150 micrograms/kg) on skin microfilarial densities was evaluated by comparing parasite levels, before and after treatment, in 192 patients living in an area endemic for onchocerciasis in North Cameroon. A mass treatment with ivermectin has been undertaken in 1989 in two villages, where pretreatment community microfilarial loads (CMFL) were 5.5 and 25.1 microfilariae per snip. The parasitological examination carried out 32 months later showed that the microfilarial densities in the adults where only 24 and 51% of the initial values, respectively. In a third village, treated once in 1989 but located in an area where annual mass distributions of ivermectin have been undertaken since 1987, the mean microfilarial density 28 months after treatment was only 12% of the initial value. In 1992, the mean microfilarial load in children had decreased significantly in comparison with those of 1989 only in the village where the level of endemicity was initially the lowest. The rate of increase in the number of skin microfilariae after one dose of ivermectin is related with the pretreatment endemicity level. The impact of large-scale ivermectin treatments on the transmission of onchocerciasis enhances the long-term efficacy of this drug on the skin microfilarial densities.

The classical method to estimate the malaria transmission in an endemic area is based on the number and infectivity of human landing mosquitoes. To compare this method with CDC Miniature Light Trap a study was carried out in a forested area of South Cameroon. Light-trap and servant were placed in six different houses of the same village from 08 p.m. to 06 a.m. In average the human landing caught 29.9 anopheline females per night, while light-trap 52.4. The ratio of light-trap on human landing was 1.75 for Anopheles genus. This ratio varied with the species: 1.88 for An. nili and 0.54 for An. gambiae s.s. Light-trap showed disadvantages, especially the lack of steadiness and the fact that only 49.6% (n = 238) of potential vectors of malaria were in good standing for dissection of salivary glands. The authors concluded that human landing remained the most efficient method of catching for the estimation of human malaria transmission in the forested area of Africa. Nevertheless, the lower cost of light-trap is an important advantage.

Three observations of sanke-bite that occurred in the Congo are reported: the bite of an aglyph colubridae (Philothamnus nitidus loveridgee) that was severe; the bite of an Atheris s.p. with moderate symptoms; the bite of a Naja melanoleuca remained totally asymptomatic.

In most of the large scale vector control programs, the larviciding operations are not fully successful, resulting in a surviving vector population due to the use of sublethal doses. This problem leads the authors to study the effect of such doses upon the future of the residual population in order to know if it represents an epidemiologically dangerous population. One insect growth regulator was selected to study this phenomenon using Onchocerca volvulus as the parasite and Simulium damnosum s.l. as the vector. The experiment was conducted under field conditions by treating a river of a savanna area in north Cameroon where onchocerciasis remains endemic. The sublethal doses yielding 20% in adult blackflies from treated larvae was determined and the effects on physiological and vectorial capacities were assessed. The authors also carried out observations on the peritrophic membrane formation and the passage of microfilariae into the hemocele. The observation of flies fed on Onchocerca after larval treatment showed that this insecticide had a light effect on female longevity but did not induce any modifications in the life cycle of the parasite. An unusual high proportion of infected females, observed by the authors, is probably due to an anomaly in the phenomenon of limitation. However, the histological analysis showed to the evidence that no apparent difference between treated and untreated blackflies was observed although the process of blood meal digestion seemed slightly altered in treated flies.

Efficacy of water source treatment with temephos 200 EC had been tested with three methods after treatment of a natural reservoir in a temporary river bed. 1. Residual pesticide in water treatment was measured with a biological test based on the pesticide toxicity on mosquito larvae from a laboratory stock for which the standard LD50 for the considered pesticide is stable and accurately known. After pesticide treatment, samples of the treated source water were taken. 30 larvae were placed in 200 ml of the treated water either pure or diluted in untreated water (ten dilutions tested). The mortality rate of larvae after 24 hours was observed and marked on a probit scale. The LD50 was read directly from the curve. The corresponding dilution of the water sample that contained one standard LD50 was expressed in mg.l-1, using the value of the standard LD50. This method was found reproducible and sensitive (up to 0.001 p.p.m.), depending on the value of the standard LD50. 2. Lethality of cyclopides was measured by numeration of survivals in 10 liters samples and compared to the natural population of a close untreated water reservoir in the higher part of the same river. Results showed that half-life of temephos was shorter than 3 days and the concentration corresponding to the LD50 for cyclopides was reached a week after treatment. Two or three weeks after treatment the cyclopide population was significant and further pesticide application was needed. 3. Decrease of incidence of dracunculiasis was compiled by weekly examination of the population during the season of transmission. Authors observed an incidence of 37% during the 86/87 season.(ABSTRACT TRUNCATED AT 250 WORDS)

Mass screening for Gambiense sleeping sickness is usually done with the Card Agglutination Trypanosomiasis Test (CATT) in series (total blood CATT followed by a serum CATT if the first test is positive) and the search for trypanosomes in cervical adenopathies. At present, the double positives (blood CATT and serum CATT) as well as the subjects in whom the trypanosome was found (in the blood or gland juice) are treated. The existence of patients whose gland punction was proved positive whereas the total blood CATT remained negative, has led the authors to make a survey with the CATT in parallel (on blood and serum CATT) on a 2,030 subjects sample in the Boko Songho site (Congo-Bouenza area). Whereas the prevalence of the positive cases to blood CATT and serum CATT (CATT in series) is 6.8%, the prevalence of the positive cases to at least one of both CATT's (CATT in parallel) is 19%. The 12.2% discordant results (blood+/serum- or blood-/serum+) have been reexamined a month later with the CATT and with the indirect Fluorescent Antibody Test (IFAT). Among these, 22.3% had become positive to blood and serum, whereas 30.6% had become negative. The latter group presents the problem of cross-reactions. The authors performed an IFAT with Trypanosoma congolense (T.c.) as antigen on an 18 subjects sample with a discordant CATT. All IFAT performed with T.c. were positive to a 1/50th threshold whereas some of the serum remained negative with IFAT when Trypanosoma brucei gambiense had been used as an antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

The lack of efficient tools is often incriminated to explain the absence of anti-vectorial activities in control programmes of vector borne diseases. However, we must recognize that the available tools are under utilized due to the lack of appropriate structures. Existing structures are reviewed. So far, results achieved by the Primary Health Care System (PHCS) are scarce. In fact, even simple methods need specific know-how for execution and specialised knowledge for planning and supervision, which differ from those needed for medical care committed to the PHCS. To develop the use of simple methods, adequate structures have to be elaborated, maintaining a peripheral character but in direct connection with a central level, which provides expertise, supervision of the activities and evaluation of the results. The association of research and operational programmes is essential to face problems linked with epidemiological, environmental, socio-economical modifications or changes in sensitivity to insecticides and for the integration of new techniques. It is also this tandem "research-control operations" which will provide the best environment for training.

An outbreak of human trypanosomiasis due to Trypanosoma brucei rhodesiense has been affecting the Busoga district of Uganda since 1976. More than 40,000 cases have been recorded up to 1990. Since two years the epidemic area has been extending to the Tororo district. The vector is Glossina fuscipes. In order to stop the disease transmission a vector control project was launched in 1988 in Busoga area. It is based on tsetse fly trapping, using pyramidal optic traps impregnated with deltamethrin (10 traps per square kilometer). The results were excellent. Everywhere fly populations were reduced by more than 95%. In some parishes flies elimination was achieved. The number of new human cases of trypanosomiasis has been reduced in the same proportions. A complete break down of the transmission in the Busoga area can be reasonably expected in the near future. Since 1990 the trapping has been extended to the epidemic areas of the Tororo District. The results after only a few months were also excellent. Because cattle in the main blood source for tsetse flies in this area, the monthly treatment of cattle with pour-on of deltamethrin has been experimented in a small area to strengthen trapping. First results are promising. The cost of the protection is 0.9 US $ per person and per year.

Insecticide treated bed nets (permethrin, deltamethrin and lambda cyalothrin) were used for malaria control in The Gambia, Burkina Faso and Tanzania where Anopheles gambiae (and An.funestus in Burkina Faso) is the main vector. Treated mosquito nets are efficient when used on a large scale and not on an individual level. Such a large scale use, acting on longevity and infectivity of vectors, always induced a decrease of malaria transmission by more than 90%. Treated bed nets had no significant effect on the overall parasite rate, showing that malaria transmission was not stopped. But it was usually found that there was a significantly smaller number of children with parasitemia higher than a critical threshold, a sensitive parameter of malaria morbidity. Indeed, in the three situations studied, malaria morbidity (fever + high parasitemia greater than critical level in the concerned area) has generally shown a similar drop of 60%. These data demonstrate that treated bed nets are useful to reduce transmission and morbidity. Advised as a new way for reduction of nuisance, treated bed nets were always welcomed by the populations and this method may be considered as a complementary weapon in public health.

Chadian refugees, most of whom are free from onchocerciasis, settled recently in a camp in a savanna area of the northern Cameroon where the prevalence is about 80% and the blindness rate is 4% of the adult population. In view of the risks of onchocerciasis facing the immigrants, the authors carried out an entomological survey in this region aimed at determining the modes of transmission and assessing the possibilities for the control of this disease. After a three-month survey in the study area, it appears clearly that 1) transmission takes place only during the rainy season, 2) the main vectors are the two savanna species, Simulium damnosum s.s. and Simulium sirbanum, 3) the larval breeding sites are not located on the principal river, the Faro, but on its small seasonal tributaries, 4) the local populations still free from onchocerciasis and the Chadian refugees who farm close to these tributaries run the risk of getting serious ocular lesions in the long run which could lead to blindness. The conclusions of this survey prompted the authors to envisage an onchocerciasis control campaign in this area against the larval stages of the vectors.

In view of the risks of onchocerciasis facing Chadian refugees who have settled in a camp in a savanna hyperendemic area of northern Cameroon, the authors concluded that a vector control directed against the black fly larvae located on small seasonal tributaries of the main water course of this area should be carried out during the four to five months of the rainy season, i.e., during the whole period of transmission of this disease. The operations were undertaken during two consecutive rainy seasons. The first year consisted in developing ground-based control techniques and evaluating the larvicidal efficacy at the larval level. The second year was, particularly, devoted to the study of the impact of the vector control on the biting rate and on the transmission of onchocerciasis. Every week, three of the tributaries close to the camp were treated with an Emulsifiable Concentrate of temephos. Throughout the rainy season, the larvicide eliminated almost all the pre-adult black fly stages on these water courses. At the point in a high onchocercal endemicity area, it also reduced the biting rate by 60% and the Annual Transmission Potential by 72%, i.e., to values corresponding to the lower meso-endemicity threshold. Since these results were obtained at a very unfavourable point from the standpoint of black fly density and onchocerciasis transmission, the authors consider that vector control carried out under these conditions protects the local populations and the Chadian refugees effectively from black fly bites and a risk of severe onchocerciasis.