Predicting West Nile virus seroprevalence in wild birds in Senegal.

West Nile fever epidemiology is complex, and the role of birds in the maintenance, amplification, and dissemination of the West Nile virus (WNV) remains partially unknown. In 2003, a serological study was performed in Senegal, where West Nile infection is considered endemic. The goal was to identify potential reservoirs of WNV among bird species present in the Ferlo area (northern Senegal) and the Senegal River Valley, and to screen the ecological factors possibly related to West Nile infection.

Using a climate-dependent model to predict mosquito abundance: application to Aedes (Stegomyia) africanus and Aedes (Diceromyia) furcifer (Diptera: Culicidae).

Mosquitoes, acting as vectors, are involved in the transmission of viruses. Thus, their abundances, which strongly depend on the weather and environment, are closely linked to major disease outbreaks. The aim of this paper is to provide a tool to predict vector abundance.

Use of sentinel chickens to study the transmission dynamics of West Nile virus in a sahelian ecosystem.

During the 2003 rainy season, a follow-up survey in sentinel chickens was undertaken to assess the seasonal transmission of West Nile virus (WNV) in a sahelian ecosystem: the Ferlo (Senegal). The estimated incidence rate in chickens was 14% (95% CI 7-29), with a very low level of transmission between July and September, and a transmission peak occurring between September and October. Comparing these results with the estimate obtained from a previous transversal serological study performed on horses the same year in the same area, the relevance of sentinel chickens in estimating the WNV transmission rate is highlighted.

Serological assessment of West Nile fever virus activity in the pastoral system of Ferlo, Senegal.

The Ferlo area (north-central Senegal) is characterized by a system of temporary ponds favorable to arboviruses among which West Nile fever (WNF) was already identified. During the rainy season in 2003, a serological study was undertaken on horses to assess the activity of the WNF virus (WNFV) in Barkedji (Ferlo). The observed serological prevalence rate was 78.

Rainfall triggered dynamics of Aedes mosquito aggressiveness.

Inspired by Davidson method of estimating daily survivals of a structureless population of mosquitoes, we present a model which describes the behavior of floodwater mosquitoes in terms of emergence functions following a rainfall event, blood feeding frequency and parous stages, and survival at various stages. As a generalization of the Davidson formula, we have developed an approach for dealing with the dynamics of structured population of mosquitoes, and derived various formulas allowing assessment of demographic parameters like durations of gonotrophic cycles and (apparent) daily survivals. The method was subsequently applied to field data of floodwater mosquitoes Aedes vexans arabiensis, potential vectors of Rift Valley fever in West Africa, collected during the 2003 rainy season in Barkedji, Senegal.

Early determination of the reproductive number for vector-borne diseases: the case of dengue in Brazil.

Objective: To evaluate a new method of deriving the reproductive number for vector-borne diseases from the early epidemic curves for vector-borne diseases with incubations in the vectors and in the hosts.

Method: We applied the model to several dengue epidemics in different climatic regions of Brazil: Brasilia, Belém, Fortaleza, Boa Vista.

Results: The new method leads to higher estimates of the reproductive number than previous models.

Influence of spatial heterogeneity on an emerging infectious disease: the case of dengue epidemics.

The importance of spatial heterogeneity and spatial scales (at a village or neighbourhood scale) has been explored with individual-based models. Our reasoning is based on the Chilean Easter Island (EI) case, where a first dengue epidemic occurred in 2002 among the relatively small population localized in one village. Even in this simple situation, the real epidemic is not consistent with homogeneous models.

Rainfall patterns and population dynamics of Aedes (Aedimorphus) vexans arabiensis, Patton 1905 (Diptera: Culicidae), a potential vector of Rift Valley Fever virus in Senegal.

The importance of rainfall for the development of Aedes vexans arabiensis populations, one of the potential vectors of Rift Valley Fever in West Africa, was demonstrated in a two-year follow-up study conducted in the Ferlo region of Senegal. In 2003, the rainy season began with heavy rains and, as a result, temporary ponds, the breeding places for mosquitoes, were flooded at their maximum level immediately. In such conditions, Aedes vexans arabiensis populations are abundant at the very beginning of the season, when the majority of eggs in quiescence are flooded.

Exposure of sheep to mosquito bites: possible consequences for the transmission risk of Rift Valley Fever in Senegal.

Rift Valley Fever (RVF) is a growing health problem in West Africa. In northern Senegal, the candidate vectors of this arbovirosis are Aedes (Aedimorphus) vexans Meigen and Culex (Culex) poicilipes Theobald (Diptera: Culicidae). Domestic ruminants are the reservoirs of the virus.

Isolation of yellow fever virus from nulliparous Haemagogus (Haemagogus) janthinomys in eastern Amazonia.

In 1998, an epizootic of yellow fever (YF) killed many howler monkeys (Alouatta spp.) in eastern Amazonia near the city of Altamira. An infection level with YF virus of approximately 3.

[Yellow fever epidemiology in Brazil].

We have carried out a meticulous time-space-analysis of the incidence of yellow fever in humans in Brazil from 1954 to 1972 and especially from 1973 to 1999. This study has added to our knowledge of the epidemiology of yellow fever and enabled us to redefine epidemiological zones and determine their geographical limits. The endemic area is located within the Amazon basin; here cases are scattered and generally limited in number.

Dengue epidemic in Belém, Pará, Brazil, 1996-97.

We describe clinical and epidemiologic findings during the first epidemic of dengue fever in Belém, Pará State, Brazil, in 1996-97. Of 40,237 serum samples, 17,440 (43%) were positive for dengue by virus isolation or serologic testing. No hemorrhagic cases or deaths were reported.

An epidemic of sylvatic yellow fever in the southeast region of Maranhao State, Brazil, 1993-1994: epidemiologic and entomologic findings.

Yellow fever virus transmission was very active in Maranhao State in Brazil in 1993 and 1994. An investigation was carried out to evaluate the magnitude of the epidemic. In 1993, a total of 932 people was examined for yellow fever from Maranhao: 70 were positive serologically, histopathologically, and/or by virus isolation, and another four cases were diagnosed clinically and epidemiologically.

[Conditions for the laboratory survival of Haemagogus janthinomys dyar, 1921 (Diptera:Culicidae)].

A little modification was made on the classical Borel tube, used for rearing isolated females of mosquitoes. The first studies were realized with the main Yellow fever vector, Haemagogus janthinomys, in Brazil. The results are: a better survival, as far as 72 days, a greater number of eggs, up to 80, and a shorter trophogonic cycle of 7-8 days.

[Epidemiology of arbovirus diseases: use and value of physiologic age determination of female mosquito vectors].

The physiological age of Yellow Fever Aedes females in Africa was studied during four years, from 1988 to 1992. We used a method, according to Polovodova's method, which looks for the "yellow body" under natural light. Those yellow bodies exist in the old females, the "parous" ones, and not in the young females, the "nulliparous" ones.

[The risk of urban yellow fever outbreaks in Brazil by dengue vectors. Aedes aegypti and Aedes albopictus].

Urban yellow fever (YF) epidemics have disappeared from Brazil since about 50 years, but a selvatic cycle still exist. In many States, cases are more or less numerous each year. Ae.