Enzootic activity of Rift Valley fever virus in Senegal.

In two areas of Senegal where previous evidence of Rift Valley fever (RVF) virus circulation was detected, Barkedji in the Sahelian bioclimatic zone and Kedougou in the Sudano-Guinean zone, a longitudinal study of the enzootic maintenance of RVF virus was undertaken from 1991 to 1993. Mosquitoes, sand flies, and ticks were collected and domestic ungulates were monitored with serologic surveys. Rift Valley fever virus was not isolated in Kedougou. In Barkedji, RVF virus was isolated from Aedes vexans and Ae. ochraceus mosquitoes collected in traps near ground pools and cattle droves and from one health sheep. Sand flies were not involved in the maintenance cycle. Seroconversions were recorded in three (1.9%) of 160 monitored sheep and goats. The interepizootic vectors appeared to belong to the Aedes subgenus Neomelaniconion in East Africa, and to the subgenus Aedimorphus in West Africa. Epizootics in East Africa are associated with an increase in rainfall. However, factors associated with epizootics remain unknown for West Africa.

[Decrease of natural immunity against Rift Valley fever in domestic ruminants of the Senegal River basin after the epizootic outbreak of 1987]. / Baisse de l'immunité naturelle vis-à-vis de la fièvre de la Vallée du Rift chez les ruminants domestiques du Bassin versant du fleuve Sénégal après l'épizootie de 1987.

A domestic ruminants serosurvey of Rift valley fever (RVF) neutralizing antibodies has been carried out during three years after the 1987 epidemic in the Senegal River Basin. Authors present results from the 1990 serosurvey that are matched with the preview surveys. Out of 1,225 ongulate tested, 17.2% had RVF virus antibodies. There is a global decrease in the herds immunity since the epizootic manifestation associated with the 1987 epidemic. Significant differences in seroprevalence are observed from the delta (28.5%) to the lower (17.9%) and middle valley (6.1%) of the Senegal river. Cattle are more likely to be with an higher seroprevalence than goat and sheep.

[Feasability of a heart valve bank in Dakar. (Preliminary study of 8 human hearts)]. / Faisabilité d'une banque d'homogreffes valvulaires cardiaque à Dakar. (Etude préliminaire sur 8 prélèvements de coeurs humains)

Authors record a preliminary study led so as to develope techniques of preparation of the cardiac homograft valves. Eight human hearts have been appropriated in the course of medico-legal autopsy. Under sterile hodd, the heart was dissected, aortic and pulmonary valves as well as a mitral valve fragment were collected for a total of 24 valvular levies. After sterlization in an antibiotic solution, valves were preserved at 4 degrees C for the mitral fragment specimen of fresh allograft and to - 196 degrees C in Nitrogen liquidates for the pulmonary and aortic valves. The control of graft quality had consisted in tests of competence during the dissection, to the evaluation of the histological study as well as tests of sterility. Cellular cultures had shown a fibroblast proliferation in 3 cases. It concerned an indeed reliable method but difficult and little sensitivity. Histological tests had shown two types of injurie: the myxoid degeneration (7 times on 8 valves) cryopreserved and a coagulative necrosis whose distribution was identical forthe two modes of conservation. Antibiotic's solution seemed to induce these injuries as do heart ischemia, and the traumatism lihleed to the great cold. The tests of sterility had shown a rate of contamination to 25 % essentially by Pseudomonas. In view of the installation of a behle of allograft bank of quality, we'll need to improve conditions of leavy, to use a freezer adaptation for progressive cryocongelation and the choice of simple method to evaluate valvular viabilty.

[Reemergence of contagious bovine pleuropneumonia in Senegal]. / Réémergence de la péripneumonie contagieuse bovine au Sénégal.

The authors have described an epizootic infection of contagious bovine pleuropneumonia (CBPP), caused by Mycoplasma mycoides subsp. mycoides biotype Small Colony (MmmSC), that has affected Ndama bovine in Lounthy village, a locality based in Bala city in the Eastern part of Senegal, during the post-rainy season in November 2012. After the cessation of vaccination, a hotbed of suspicion of CBPP was identified on November 3rd 2012 in the village of Lounthy: out of the total of 98 cattle, 13 animals were sick and 5 of them died. These studies have been done according to clinical aspects, serological, bacteriological and molecular analysis of the samples. This reemergent disease will give new orientations for CBPP control in Senegal, where it was supposed the disease has been eradicated since 2005.

Endemic transmission of Rift Valley Fever in Senegal.

Rift Valley fever (RVF) is an expanding zoonotic disease transmitted from ruminant to ruminant by Culicidae mosquitoes. In 2004, a longitudinal serological survey was performed on small ruminants in the Ferlo are (Senegal) to study RVF transmission and compared the results with those obtained from the same study in 2003. The results confirm that the disease is endemic and that the spatial transmission of RVF is highly heterogeneous. The virus could be maintained during dry season by transovarian transmission in Aedes vexans. Further studies are needed to improve the understanding of the epidemiological cycle of RVF in this region to implement adapted surveillance measures.

Changes in Rift Valley fever neutralizing antibody prevalence among small domestic ruminants following the 1987 outbreak in the Senegal River basin.

Following the Rift Valley fever (RVF) epizootic of 1987 in the Senegal River basin, 2 series of serosurveys were carried out. In 1988 and 1989, respectively, 303 and 331 randomly selected sheep and goats were investigated and sera tested for the presence of specific RVF-virus-neutralizing antibodies. In 1988, 24.4% of the sera was found to have anti-RVF neutralizing antibodies and in 1989, 19.3% was found. In 1988, we observed in the Dagana district, including the 1987 epizootic area, a significantly higher prevalence (71.1%) than in the two other more distant districts of Podor (21.5%) and Matam (9.7%). From 1988 to 1989, the antibody seroprevalence dropped significantly from 71.7 to 23.9% within the Dagana district. Young animals showed a significantly lower antibody prevalence (7.9%, N = 114) than adults (25.3%, N = 217). RVF virus circulated at a low level in 1988-89 without any epizootic manifestation. The population turnover generated an important non-immune population potentially at risk.

Rift valley fever surveillance in the lower Senegal river basin: update 10 years after the epidemic.

After the Rift valley fever (RVF) epidemic of 1987 in the Senegal River Basin, RVF surveillance based on serosurveys has been conducted for 10 years. Serum samples were obtained from 1336 persons and from sheep and goats in selected areas, and these were tested for IgG/IgM RVF antibodies by ELISA. After a period of regular decrease in RVF prevalence in domestic animals until 1993, an epizootic was observed in all herds in 1994-95 with increases in IgM levels and abortions. During the same period, no human cases or RVF IgM were detected. The RVF IgG prevalence significantly correlated with date of birth: children born after 1987 have a low prevalence (5%) in clear contrast to the older population (25.3%) in Podor district. A retrospective analysis of rainfall and RVF prevalence in small domestic animals over the last 10 years showed that the re-emergence correlated with heavy rainfall. A general analysis of the risk of re-emergence and the efficiency of this RVF surveillance system are presented.

Variability of the NS(S) protein among Rift Valley fever virus isolates.

Eighteen strains of Rift Valley fever (RVF) virus collected over a period of 38 years and isolated from diverse localities in Africa and from various hosts (human, animal and arthropod) were investigated by RT-PCR followed by sequencing of the NS(S) protein coding region. This region was chosen to analyse variability because, in contrast to the N protein, the NS(S) protein differs in various phleboviruses and there exists an RVF virus (clone 13) in which 70% of the NS(S) ORF is deleted, suggesting that this sequence is under a weak selective pressure. Sequence data indicated that percentage divergence among isolates ranged from 0 to 9.6% at the nucleotide level and from 0 to 9.5% at the amino acid level. Phylogenetic analysis based on the NS(S) gene revealed two major lineages: Egyptian and sub-Saharan. This led to the establishment of the relatedness between strains and insights into the NS(S) protein, the function of which is still undetermined. Alignment of the deduced amino acid sequences indicated that the cysteine residues are conserved, as are several motifs representing potential phosphorylation sites.

Genetic reassortment of Rift Valley fever virus in nature.

Rift Valley fever virus (RVFV), a phlebovirus of the Bunyaviridae family, is an arthropod-borne virus which emerges periodically throughout Africa, emphasizing that it poses a major threat for animal and human populations. To assess the genetic variability of RVFV, several isolates from diverse localities of Africa were investigated by means of reverse transcription-PCR followed by direct sequencing of a region of the small (S), medium (M), and large (L) genomic segments. Phylogenetic analysis showed the existence of three major lineages corresponding to geographic variants from West Africa, Egypt, and Central-East Africa. However, incongruences detected between the L, M, and S phylogenies suggested that genetic exchange via reassortment occurred between strains from different lineages. This hypothesis, depicted by parallel phylogenies, was further confirmed by statistical tests. Our findings, which strongly suggest exchanges between strains from areas of endemicity in West and East Africa, strengthen the potential existence of a sylvatic cycle in the tropical rain forest. This also emphasizes the risk of generating uncontrolled chimeric viruses by using live attenuated vaccines in areas of endemicity.