Malaria transmission in Southern Madagascar: influence of the environment and hydro-agricultural works in sub-arid and humid regions. Part 1. Entomological investigations.

A 4-year entomological study was carried out in Southern Madagascar to identify malaria vectors, evaluate the transmission and compare the influence of irrigation in the sub-arid and adjacent humid regions. Three villages were involved in this entomological survey: Androvasoa (located in the natural sub-arid ecosystem), Pépiniére (sited at the centre of an irrigated rice scheme in the sub-arid region) and Esana (bordered with rice fields in the humid region). Mosquitoes were collected inside and outside dwellings when landing on human beings, with light traps and with knockdown indoor sprays. Anopheles arabiensis, Anopheles merus and Anopheles funestus were found in every village while Anopheles gambiae s.s. was only found in the village bordering the rice-fields (Pépiniére) and Anopheles mascarensis, a mosquito native to Madagascar, was only found in the humid region (Esana). In Pépiniére, the annual entomological inoculation rate (EIR) was low (EIR=0.4 infective bites/man/year (IBM)). In the irrigated scheme of the sub-arid region, malaria transmission was 150 times higher (mean EIR=63 IBM) than in the natural ecosystem and A. funestus was the main vector, responsible for 90% of infective bites. In Esana, the level of malaria transmission was high (EIR=41 IBM) and 2/3 of the infective bites were due to A. mascarensis, despite the presence of A. gambiae s.s. and A. funestus. These results are discussed with reference to the impact of irrigation on malaria in Africa ("the paddies paradox").

Suburban transmission of Q fever in French Guiana: evidence of a wild reservoir.

The annual incidence of Q fever in French Guiana was found to have increased in 1996 and was 37/100,000 population over the last 4 years. Subsequent investigations in Cayenne and its suburbs indicated that a wild reservoir of the bacteria was responsible for the epidemiologic pattern. A case-control study showed that residence near a forest and occupations and activities that result in exposure to aerosols of dusts from the soil are risk factors for Q fever. By means of time-series analysis, a strong positive correlation between rainfall and the incidence of Q fever with a time lag of 1-3 months was found. The spatial distribution of the cases showed that transmission occurs widely throughout greater Cayenne, which is incompatible with a pinpoint source of contamination. Transmission from livestock and dissemination of the bacteria by the wind appeared to be unlikely, which strengthens the hypothesis that a wild reservoir is responsible for transmission.

Tonate virus infection in French Guiana: clinical aspects and seroepidemiologic study.

Two recent cases of human infection with Tonate virus, one of which was a fatal case of encephalitis, have renewed interest in these viruses in French Guiana. The clinical aspects of confirmed and probable cases of infection with this virus indicate that it has pathogenic properties in humans similar to those of other viruses of the Venezuelan equine encephalitis complex. To determine the prevalence of antibodies to Tonate virus in the various ethnic groups and areas of French Guiana, 3,516 human sera were tested with a hemagglutination inhibition test. Of these, 11.9% were positive for the virus, but significant differences in seroprevalence were found by age, with an increase with age. After adjustment for age, significant differences were found between places of residence. The prevalence of antibody to Tonate virus was higher in savannah areas, especially in the Bas Maroni (odds ratio [OR] = 22.2, 95% confidence interval [CI] = 15.2-32.4) and Bas Oyapock areas (OR = 13.4; 95% CI = 9.8-18.4). The ethnic differences observed in this study were due mainly to differences in place of residence, except that whites were significantly less frequently infected than other ethnic groups. This study indicates that Tonate virus infection is highly prevalent in French Guiana, especially in savannah areas.

[Evaluation of the vectorial capacity of Anopheles arabiensis (Diptera:Culicidae) on the island of Réunion: an approach to the health risk of malaria importation in an area of eradication]. / Evaluation de la capacité vectorielle d'Anopheles arabiensis (Diptera: Culicidae) à l'île de La Réunion: une approche du risque sanitaire lié au paludisme d'importation en zone d'éradication.

Following intensive control measures, malaria was eradicated from La Réunion Island (Indian Ocean) in 1979. However, potential vectors remain in coastal areas and, each year Public Health Services detect some imported cases from surrounding countries. Anopheles arabiensis is the only species which can be responsible for local transmission though its brief life cycle and its exophilic and zoophilic behaviour were found to be key elements in maintaining the eradication status of the disease on the island. Its vectorial capacity was measured at different seasons and in different areas with a view to assessing the health risks due to imported malaria and suggesting a more pertinent strategy of vector control.

[Anopheles mascarensis (De Meillon, 1947): main vector of malaria in the region of Fort-Dauphin (south-east of Madagascar)]. / Anopheles mascarensis (De Meillon, 1947): vecteur principal du paludisme dans la région de Fort-Dauphin (Sud-est de Madagascar).

Anopheles funestus and Anopheles gambiae s.l. have been considered until now the major vectors of malaria everywhere in Madagascar. Anopheles mascarensis, a mosquito native to Madagascar, has been identified in Sainte-Marie island as a secondary vector only. In 1997, an entomological study was carried out to identify the malaria vectors in the area of Fort-Dauphin, South-East of Madagascar. Every month, mosquitoes were collected from landing catches on human volunteers (from 7:00 am to 5:00 pm inside dwellings and from 7:00 am to 0:00 pm outside) and from knockdown spray-collections indoors. An mascarensis was the most abundant mosquito, the average number of An. mascarensis bites per man/night was 7.6. The sporozoite index was 0.89%. Despite the presence of An. funestus and An. gambiae s.l., An. mascarensis was found to be responsible for 2/3 of the infectious bites (25 infectious bites per man/year). An. mascarensis is widely distributed ih Madagascar but only specimens from the east coast have been found to carry sporozoites of human malaria. Further arguments are thus advanced for the hypothesis according to which a sibling species of An. mascarensis is present in Madagascar.

[Update on plague in Madagascar]. / Actualités sur la peste à Madagascar.

After a thirty year period of successful control, bubonic plague showed the first signs of return in Madagascar where a fatal outbreak occurred in Antananarivo in 1978. A second outbreak was observed in Mahajanga in 1991 after more than a half century. In 1997, 459 confirmed or presumptive cases were reported, as compared to 150 to 250 cases during the last years. However the actual extent of this recrudescence must be placed in the perspective of a more efficient control program that has led to better reporting of suspected cases and availability of more accurate diagnostic techniques. Recent research has led to the development of highly effective immunological diagnostic tools (detection of antibodies and F1 antigen) allowing not only better surveillance of the disease in man and animals but also renewed study of the epidemiological cycle in the current environment. In this regard the capacity of several endemic fleas as vectors and the role of the rat Rattus norvegicus and the musk shrew Suncus murinus are currently under investigation. Genetic study of strains collected from 1936 to 1996 has demonstrated the appearance of 3 new ribotypes of Yersinia pestis since 1982 in the zones of strongest plague activity in Madagascar. A strain showing multiresistance to standard therapeutic antibiotic agents was isolated in 1995. Bubonic plaque is a priority health problem in Madagascar but remains a major concern for the rest of the world.

[Malaria in Antananarivo: evaluation of a post-epidemic situation]. / Le paludisme à Antananarivo: évaluation d'une situation post-épidémique.

Antananarivo has a population of close to one million inhabitants and is located in the highlands of Madagascar. The capital was, until some years ago, thought to be a malaria transmission-free zone. However, between 1985 and 1990, several malaria cases occurred in the suburbs of Antananarivo, along the Ikopa river (the Betsimitatatra Plain), suggesting that local transmission was occurring. Numerous malaria cases have since been reported by health workers each year, but there is insufficient epidemiological information about the cause and origin of the transmission, because cases are rarely confirmed by parasitological examination. The National Malaria Control Management in Madagascar has, after four years of intensive DDT spraying campaigns in the highlands, stopped this specific method of control. Epidemiological follow-up studies will be carried out to evaluate the effects on malaria transmission of this cessation of control measures. The transmission of malaria in Antananarivo was studied from 1995 to 1996. Patients from nine health centers in various suburbs of Antananarivo were included in the study, with the presence of fever used as the sole inclusion criterion. Children randomly selected from schools in the same area were included in a second study group. A blood sample was obtained from each participant to determine the parasite index and the prevalence of antibodies against P. falciparum. The splenic index was also determined. A second assessment was performed for the school children six months later, using the same markers of malaria infection. Nine hundred and thirty two patients from the health center group were referred for participation in the study. This represented 10% of all patients and 74% of the patients with fever. The school group included 1,545 children. The splenic index was similarly low (0.5%) in the health center and school groups, as was the overall parasite index (2.6% for the health center group and 0.8% in the school group). The prevalence of antibodies against P. falciparum was also low, but with a seasonal variation: 2.5% in June 1995 and 11.6% in January 1996. Almost all the cases confirmed by parasitological examination were due to the patient having stayed in an area with hyperendemic malaria or having been in contact with an individual who had been to an area with a high level of transmission. Our findings confirm that Antananarivo is now in a post-epidemic situation. Malaria cases are mostly associated with a history of travel in areas with high levels of malaria transmission, particularly the coastal regions of Madagascar. Nevertheless, a low level of transmission may persist and lead to further outbreaks of malaria in the future, due to the presence in the area of Anopheles arabiensis.

Evolution of malaria in Africa for the past 40 years: impact of climatic and human factors.

Different malarial situations in Africa within the past 40 years are discussed in order to evaluate the impact of climatic and human factors on the disease. North of the equator, more droughts and lower rainfall have been recorded since 1972; and in eastern and southern Africa, there have been alternating dry and wet periods in relation to El Niño. Since 1955, the increase in human population from 125 to 450 million has resulted in both expansion of land cultivation and urbanization. In stable malaria areas of West and Central Africa and on the Madagascar coasts, the endemic situation has not changed since 1955. However, in unstable malaria areas such as the highlands and Sahel significant changes have occurred. In Madagascar, cessation of malaria control programs resulted in the deadly epidemic of 1987-88. The same situation was observed in Swaziland in 1984-85. In Uganda, malaria incidence has increased more than 30 times in the highlands (1,500-1,800 m), but its altitudinal limit has not overcome that of the beginning of the century. Cultivation of valley bottoms and extension of settlements are in large part responsible for this increase, along with abnormally heavy rainfall that favored the severe epidemic of 1994. A similar increase in malaria was observed in neighboring highlands of Rwanda and Burundi, and epidemics have been recorded in Ethiopia since 1958. In contrast, in the Sahel (Niayes region, Senegal), stricken by droughts since 1972, endemic malaria decreased drastically after the disappearance of the main vector, Anopheles funestus, due to the destruction of its larval sites by cultivation. Even during the very wet year of 1995. An funestus did not reinvade the region and malaria did not increase. The same situation was observed in the Sahelian zone of Niger. Therefore, the temperature increase of 0.5 degree C during the last 2 decades cannot be incriminated as a major cause for these malaria changes, which are mainly due to the combination of climatic, human, and operational factors.

[The impact of curtains impregnated with deltamethrin on the vectors and morbidity of malaria: results in Ankazobe, on the plateaus of Madagascar]. / Impact des rideaux imprégnés de deltaméthrine sur les vecteurs et la morbidité palustre: résultats à Ankazobe, sur les plateaux de Madagascar.

To evaluate the efficacy of deltamethrin impregnated curtains on malaria morbidity in a low transmission area, we studied volunteer families in the village of Ankazobe in the Madagascar Highlands from February 1993 to June 1994. After randomization, we provided 46 houses having 244 inhabitants with impregnated curtains (I) and 45 others having 257 inhabitants with nonimpregnated curtains (NI) as controls. We first estimated the number of mosquito bites in the protected versus nonprotected households. Every month, we captured mosquitos on humans in 6 houses per night for 4 nights. For the I group compared to the NI group, the number of bites by the Anopheles funestus vector per human per night was reduced by 64% in 1993 and 39% in 1994. We also analyzed the malaria morbidity. Malaria morbidity was defined as patients having both temperatures greater than 37.5 degrees C and Plasmodium falciparum parasitemia greater than 1500/microliter with clinical symptoms. From February to July 1993, we observed no significant difference in morbidity: there were 103 cases of malaria among 244 inhabitants of the I group and 117 cases among 257 inhabitants of the NI group. However, during the period of highest transmission from March to May in 1993, there were significantly fewer cases in the I group (68) than in the NI group (94). From January to June 1994, the difference was clear: only 35 malaria cases were observed among the 208 inhabitants of the I group as compared to 65 cases among the 223 inhabitants of the NI group (Chi square = 9.17, p = 0.0024). Inhabitants of the I group could have been contaminated before the curtains were set up. After treatment of the cases and use of curtains during the second year, we observed a reduction in the number of mosquito bites and malaria cases. The small size of the trial made the interpretation of the data difficult. Nonetheless, the results tentatively support the use of impregnated curtains as an antimalaria tool in an integrated control program.

[The reconquest of the Madagascar highlands by malaria]. / La reconquête des Hautes Terres de Madagascar par le paludisme.

A strong malaria epidemic with a high mortality rate occurred on the Madagascar Highlands in 1986-88. Vector control and free access to antimalaria drugs controlled the disease. The authors have searched for the causes of the epidemic to propose a strategy avoiding such events. The Highlands on Madagascar were known as malaria free. In 1878 a very severe epidemic flooded all the country. Development of irrigated ricefields which house both An. arabiensis and An. funestus had created a new anthropic environment. Moreover manpower imported from malarious coastal areas for rice cultivation and also for building large temples, could have brought P. falciparum. After several outbreaks the disease became endemic up to 1949. In 1949 a malaria eradication programme based on DDT spraying and drug chemoprophylaxis and chemotherapy was launched. By 1960 malaria was eliminated and DDT spraying cancelled. Only 3 foci were kept under surveillance with irregular spraying until 1975. The prophylaxis and treatment centres ("centres de nivaquinisation") were kept open up to 1979. The catholic dispensary of Analaroa, 100 km N.E. of Tananarive, opened in 1971 and worked without interruption up to now. The malaria diagnosis has always been controlled by microscopy. Its registers are probably the more reliable source of information on malaria in the area. They show that malaria was already present on the Highlands in 1971 but at a low prevalence; in 1980 when the "centres de nivaquinisation" were closed the number of cases increased by three times the progressive increase of the number of cases became exponential from 1986 to 1988 which was the peak of the epidemic; malaria remained at a high level until the end of 1993; yearly DDT spraying since 1993 have decreased the number of malaria cases among the dispensary attendants by 90%. The epidemic peak of 1988 was well documented by the Pasteur Institute of Madagascar around Tananarive. Before the epidemic started it was observed a come back of An. funestus which had been previously eliminated of most of the villages by DDT spraying. More than an epidemic the malaria increase in 1988 was a reconquest by malaria of the land from which it had been eliminated in the years 1950. This episode became dramatic because the lack of immunity of the population and the shortage of medicaments. The global warming which was advocated to explain the epidemic has no responsibility because the temperature on the Madagascar Highlands has not changed during the last 30 years. Also the cyclones do not seem to have played any role. It is very likely that the gradual decline of control measures, first DDT spraying, later drug distributions, had the main responsibility in the Highlands drama. Everywhere An. funestus reached a high level during the time where the parasite reservoir was rebuilding. They synergised each other. These findings should be taken in account in drawing the strategy planning for the next years.

[Rice: source of life and death on the plateaux of Madagascar]. / Le riz source de vie et de mort sur les plateaux de Madagascar.

Since the 17th century, Europeans travelling in Madagascar described the contrast between the fever-free Plateau and the fever-ridden coasts. The former were inhabited by people of Asiatic origins and the latter by African migrants. At the end of the 18th century, "Merina" kings developed land irrigation and rice cultivation, using manpower from the coasts. Since then, rice has become a monoculture covering most of the arable lands of the Highlands. The first malaria epidemic occurred in the Tananarive area in 1878, and rapidly spread throughout the Plateau. The mortality rate was high. A second epidemic in 1895 may have been a resurgence of the previous one. Subsequently, malaria became meso-epidemic despite control measures, mainly consisting of larvivorous fishes, quinine treatment and prophylaxis. In 1949, an eradication program was launched based on DDT house-spraying and chloroquine prophylaxis in children. It was very successful on the Highlands where malaria disappeared, in 1962. Spraying was cancelled and only three small foci remained under surveillance. In 1987 and 1988, a malaria outbreak devastated the plateau. Subsequently, intensive spraying operations brought the situation under control by 1993. The main malaria vector on the Madagascar Highlands is An. funestus. More than 95% of its breeding sites are in the rice fields just before the harvest and afterwards in the fallow lands. The vector peak and the corresponding peak of malaria cases occur between February and May, depending on the farming calender. The second but less important vector, An. arabiensis, breeds in the rice fields just after seeding when the surface water is sunlit. Although rice fields remain the main source of this vector, it also breeds in rainwater pods and borow-pits. Malaria vectors on the plateau are products of human activities of rice cultivation, which is the basis of the economy. The epidemiological importance of rice fields varies greatly from one country to another. In Southeast Asia, the rice fields harbor several anopheline species most of which are only vectors of P. vivax. In West Africa where malaria is holoendemic, they produce large populations of An. gambiae; however, the malaria pattern is unaltered and remains at peak levels. In the dry areas of southern Madagascar, the vector An. funestus and meso-hyperendemic malaria are restricted to areas of cultivated rice. In West and Central Africa, An. funestus is never found in rice fields even though it is common in marshes. In Madagascar, this vector breeds in irrigated rice fields. Because it is practically impossible to control anophelines in rice fields by chemical, biological and ecological methods on the Highlands of Madagascar, house-spraying remains the best method for mass malaria control. Bed-nets impregnated with pesticides may offer an alternative, but their use is resisted by the local population.

[Malaria: research perspectives in medical entomology in Madagascar]. / Paludisme: perspectives des recherches en entomologie médicale a Madagascar.

The entomological studies on malaria in Madagascar had especially concerned the behavior of vectors in relation to insecticides. The cessation of spraying within the homes and the absence of chloroquine allowed a re-emergence of malaria on the Plateau in the 1980's. This phenomenon pointed out the heterogeneity of the transmission on the island. It was necessary to define the entomological characteristics of the four principal facies of transmission in Madagascar. These studies provided the services of public health with the epidemiological basis to organize the measures of the battle and prevention of malaria. In the very populated countryside of the Plateau, the nature of the vectors, their density and their vectorial competence present large local variations. The entomological studies search to define the different human and environmental factors which modulate the transmission and constitute the risk factors of epidemy. This micro-epidemiological approach will facilitate the analysis and comparison of the clinical and biological results obtained in the different residences. The research on medical entomology will equally enable the proposal of plans for the fight against malaria adapted to the different situations.

[Anopheles funestus and rice agriculture in the Madagascar highlands]. / Anopheles funestus et la riziculture sur les plateaux de Madagascar.

An exhaustive study of the potential habitats of Anopheles funestus was led during 1992 in Ankazobe on the Plateau of Madagascar, 95 km northwest of the capital Tananarive. The rice fields provide more than 90% of the positive habitats versus less than 10% for the nonhuman biotopes. Larva are especially abundant on the surfaces of the rice during grain head formation and maturation. The dense vegetation coverage provides them with shade and protection against predators. After harvesting, the follows can be filled with water and wild vegetation, and then also provide an important share of the habitats. The rice fields are omnipresent on the Plateau where they supply the basis of local alimentation. A. funestus then constitutes a serious risk for all of the villages. The role of the rice fields as habitats for A. funestus has already been noted in Kenya but in West Africa the rice fields do not host this species, even if this species is very abundant in the other types of habitats.

[Dengue 1 epidemic in the Grand Comoro Island (Federal Islamic Republic of the Comores). March-May 1993]. / Epidémie de dengue 1 sur l'île de la Grande Comore (République Fédérale Islamique des Comores). Mars-mai 1993.

An epidemic of dengue fever occurred in Grande Comore island from March to May 1993. Dengue 1 virus has been isolated. The epidemic did not affect the other islands of the archipelago. No compound clinical picture, in particular hemorrhagic, was reported. A random sampling survey conducted towards the end of April showed that 26% of the population aged 5 years old or more had IgM dengue antibodies. The epidemic concerned essentially individuals under 45 years of age. The number of inhabitants of Grande Comore affected by the outbreak can be estimated between 56,000 and 75,000. The results of the sero-epidemiological survey allowed to find the serological scar of two previous epidemics of dengue: the first one around 1948, which may correspond with dengue 1, the other one in 1984, probably with dengue 2.

[Epidemiological malaria surveillance in 3 villages of the Madagascar highlands]. / Surveillance épidémiologique du paludisme dans trois villages des Hautes Terres Malagaches.

Results of the epidemiological surveillance of falciparum malaria carried out since 1987 in three villages of the malagasy Highlands are reported. They clearly show the unsteady endemo-epidemic characteristic of the disease with highly variable transmission levels according to foci. At Manarintsoa, a south-western village 20km away from the Capital, the disease has now fully disappeared after the ravage of 1986. But it might reappear with new imported cases and by lack of antivectorial measures. Although Anopheles arabiensis had been rare and its aggressivity rate weak (0.91-2 infecting bites per year per man), surveillance is indispensable for the future. An Ankazobe and Mahavelona, two north-western localities respectively 100km and 65km away from Antananarivo, malaria is endemic with periodic outbreaks during rainy season. At Ankazobe, Anopheles funestus is the main vector maintaining endemic in this area while the role of Anopheles gambiae l.s. is only secondary. At Mahavelona, because of the weak presence of vectors, the treatment protocol by Quinimax has been applied in order to study transmission. This study obviously shows that contrary to set ideas in the Highlands, backward transmission is possible up to the first months of the austral winter (June-July). In these two last villages, adults have acquired some premunition.

[Epidemiological stratification of malaria in Madagascar]. / Stratification épidémiologique du paludisme à Madagascar.

Madagascar is considered as a sub-region of the Afrotropical geographical Region in spite of the high endemicity of 95% of the invertebrates. Nevertheless the three malaria vectors An. gambiae s.s., An. arabiensis and An. funestus are quite similar to those of the continental Africa. This support the hypothesis of their recent introduction. Plasmodium falciparum is the dominant parasite but the prevalence of P. vivax is not negligible. It is linked to the Asian component of the human population. P. malariae and P. ovale are of minor importance. The main epidemiological "facies" of Africa are found in Madagascar. The equatorial facies on the East Coast is characterized by a high transmission all year long. In the tropical facies on the West Coast transmission is seasonal (7 months at least). In both areas, malaria is stable and the inhabitants acquire a high immunity before the age of ten; most of the severe cases touch children below 10. The three vectors can be found but An. gambiae s.s. is dominant. In the exophilic southern facies the transmission is seasonal (two to four months). The only vector is An. arabiensis. Malaria is unstable and severe epidemics occur during the years of high rainfall. All age groups are vulnerable because the population is not immune in the Plateaux facies above 1,000 m., malaria is unstable. Severe epidemics occurred in 1987-1988. The vectors are An. Arabiensis and An. funestus. The occurrence of P. falciparum on the Plateaux seems linked to the development of irrigation of rice farming in the XIXth century. Most of the anopheles breeding places on the Plateaux are dependent on rice cultivation. Urban development has brought the inhabitants of the suburbs in close contact with rice fields. Despite the high number of anopheline bites the number of malaria cases remains by far lower than in the neighbouring rural areas. Regional migrations inside the island bring non-immune populations, from the south and the plateaux, in highly malarious areas of the coast, where the migrants are exposed to high risk. In spite of 40 years of uncontrolled use, chloroquine can still cure most, if not all, of malaria cases. Control measures appropriated to the different areas of Madagascar are discussed.

Rift Valley fever epizootic in the central highlands of Madagascar.

Between February and April 1991, unusual numbers of bovine abortion around Antananarivo (central highlands, Madagascar) were reported by official veterinary services. Rift Valley fever (RVF) virus isolations were made from sixteen aborted foetuses and one dead calf in different foci. Using monoclonal antibodies, the isolated viruses were found to be different from the 1979 RVF strains isolated in Madagascar from mosquitoes and human laboratory infection, and closer to African RVF strains. In a bovine population--previously characterized by a negative or very low RVF antibody prevalence--a high prevalence of IgM antibodies (264/994: 26.5% positive) was revealed; the IgM prevalence in recently aborting females varied from 40 to 91%. Among 994 human sera tested by IgG-IFA (immunofluorescent antibody assay) and IgM ELISA, 8.2% and 4.5%, respectively, proved positive. A total of 11,371 mosquitoes (61% Culex antennatus) were collected in the epizootic areas and tested without any virus isolation. Extensive studies were conducted to determine the geographical extension and the impact of this epidemic on the highly susceptible livestock and human populations.