A Bayesian network approach to the study of historical epidemiological databases: modelling meningitis outbreaks in the Niger

Objective

To develop a tool for evaluating the risk that an outbreak of meningitis will occur in a particular district of the Niger after outbreaks have been reported in other, specified districts of the country.

Methods

A Bayesian network was represented by a graph composed of 38 nodes (one for each district in the Niger) connected by arrows. In the graph, each node directly influenced each of the “child” nodes that lay at the ends of the arrows arising from that node, according to conditional probabilities. The probabilities between “influencing” and “influenced” districts were estimated by analysis of databases that held weekly records of meningitis outbreaks in the Niger between 1986 and 2005. For each week of interest, each district was given a Boolean-variable score of 1 (if meningitis incidence in the district reached an epidemic threshold in that week) or 0.

Findings

The Bayesian network approach provided important and original information, allowing the identification of the districts that influence meningitis risk in other districts (and the districts that are influenced by any particular district) and the evaluation of the level of influence between each pair of districts.

Conclusion

Bayesian networks offer a promising approach to understanding the dynamics of epidemics, estimating the risk of outbreaks in particular areas and allowing control interventions to be targeted at high-risk areas.     

The adaptation of Rice yellow mottle virus to the eIF(iso)4G-mediated rice resistance

The rymv1-3 allele of the eIF(iso)4G-mediated resistance to Rice yellow mottle virus (RYMV) is found in a few Oryza glaberrima cultivars. The same resistance-breaking (RB) mutations emerged in the central domain of the VPg after inoculation of isolates of different strains. The RB mutations were fixed, often sequentially, at codons 41 and 52 which paralleled an increase in virus accumulation. RB mutations also emerged after inoculation of an avirulent infectious clone, indicating that they were generated de novo in resistant plants. Only virus isolates with a threonine at codon 49 of the VPg broke rymv1-3 resistance, those with a glutamic acid did not. A small subset of these isolates overcame rymv1-2 resistance, but following a specific pathway. Comparison with the RB process of rymv1-2, a resistance allele found in a few Oryza sativa cultivars, showed similarities in the mode of adaptation but revealed converse virulence specificity of the isolates.     

Serotype Diversity of Foot‐and‐Mouth‐Disease Virus in Livestock without History of Vaccination in the Far North Region of Cameroon

Little information is available about the natural cycle of foot‐and‐mouth disease (FMD) in the absence of control measures such as vaccination. Cameroon presents a unique opportunity for epidemiological studies because FMD vaccination is not practiced. We carried out a prospective study including serological, antigenic and genetic aspects of FMD virus (FMDV) infections among different livestock production systems in the Far North of Cameroon to gain insight into the natural ecology of the virus. We found serological evidence of FMDV infection in over 75% of the animals sampled with no significant differences of prevalence observed among the sampled groups (i.e. market, sedentary, transboundary trade and mobile). We also found antibodies reactive to five of the seven FMDV serotypes (A, O, SAT1, SAT2 and SAT3) among the animals sampled. Finally, we were able to genetically characterize viruses obtained from clinical and subclinical FMD infections in Cameroon. Serotype O viruses grouped into two topotypes (West and East Africa). SAT2 viruses grouped with viruses from Central and Northern Africa, notably within the sublineage causing the large epidemic in Northern Africa in 2012, suggesting a common origin for these viruses. This research will guide future interventions for the control of FMD such as improved diagnostics, guidance for vaccine formulation and epidemiological understanding in support of the progressive control of FMD in Cameroon.     

蒿甲醚胶囊治疗非洲黑色人种恶性疟疾的临床疗效

全世界每年有3～5亿的疟疾患者，其中90％发生在非洲。长期以来。在非洲广泛应用并被认为是抗疟特效药的盐酸间苯二酚奎宁（Quinimax），其用量越来越大。而另一种抗疟药青蒿素（Arteminin）对各种疟原虫红内期无性体具有强力杀灭作用，能有效缓解症状和杀灭疟原虫，但青蒿素在尼日尔的市场占有率非常低。为提高对该药的认识，我们在尼日尔共和国马拉迪住院中心工作3年期间，应用国产蒿甲醚胶囊和法国生产的盐酸间苯二酚奎宁注射液治疗非洲黑色人种恶性疟疾，进行临床疗效比较，现报道如下。     

Characterization of transboundary foot‐and‐mouth disease viruses in Nigeria and Cameroon during 2016

Continuous surveillance for foot‐and‐mouth disease (FMD) in endemic settings such as West Africa is imperative to support improved local and regional control plans, with the long‐term goal of regional eradication. This paper describes the genetic characterization of FMD viruses (FMDV) obtained from outbreaks in Nigeria (n = 45) and Cameroon (n = 15) during 2016 and from archival samples (n = 3) retrieved from a 2014 outbreak in Nigeria. These viruses were analysed in the context of previously published FMDV sequences from the region. Four FMDV serotypes: O, A, SAT1 and SAT2, were detected. Phylogenetic analyses of the VP1 coding sequences indicate the continuity of FMDV serotype O East Africa‐3 (O/EA‐3), serotype A AFRICA genotype G‐IV (A/AFRICA/G‐IV) and serotype South African Territories (SAT) 2 lineage VII (SAT2/VII). The FMDV SAT1 topotype X (SAT1/X), which emerged in Nigeria in 2015, continued to be associated with outbreaks in the region during 2016, and SAT1 is reported for the first time from Cameroon. Additionally, a re‐emergence or re‐introduction of the serotype O West Africa (O/WA) topotype in Nigeria is described herein. Our findings indicate a consistent, pan‐serotypic relationship between FMDV strains detected in Cameroon and Nigeria. Additionally, FMDV strains from West Africa obtained in this study were genetically related to those occurring in East and North Africa. These phylogenetic relationships suggest that animal movements (pastoralism and/or trade) are important factors for virus spread across the African continent. These data provide critical baselines which are a necessary component of Stages 0 and 1 of the Progressive Control Pathway of FMD (PCP‐FMD). Specifically, characterizing the existing virus strains (risk) provides the basis for the comprehensive risk‐based control plan which is the requisite criteria for Nigeria's transition to Stage 2 of PCP‐FMD, and for coordinated regional control of FMD.     

Pregnancy among single women in Niamey (Niger)

The objectives of this study are to describe the socio-economic profile of single mothers and to specify the influence of this status on pregnancy and delivery. Between April 1995 and February 1996, a cohort study in Niamey allowed the selection of 181 single mothers, matched by age and parity with married pregnant women living in the same district. We used the McNemar's and Wilcoxon's statistic tests. In parallel, qualitative open interviews were conducted with patients and health care providers. Single mothers represent 6.1% of the study population. The median age was 19 years and 72% were primiparas. They received some level of education, at least primary and were well integrated in their districts. Twenty four per cent were employed and 31% had no income. Single mothers' attendance and punctuality at prenatal care centre were not as good as married women and also as their compliance with iron prophylactic treatment. The mode of delivery was identical but the risk of low birthweight infant was 2.4 more frequent in single mothers. Finally, knowledge of contraceptive methods and access to them were identical, but single mothers used them more frequently than married women.     

Molecular epidemiology of peste des petits ruminants in Niger: An update

Like many West African countries, outbreaks of peste des petits ruminants (PPR), an economically important disease of goats and sheep, are regularly reported in Niger. The causative virus, peste des petits ruminants virus (PPRV), can be differentiated into four genetically distinct lineages. A publication in 2018 identified three PPRV lineages circulating in the country in 2001 (lineages I and II) and 2013 (lineage IV), respectively. In this present study, more recent samples were collected from goats and sheep in locations throughout Niger between 2011 and 2017. Twelve PPRV‐positive samples were characterized by sequencing of a segment of the nucleocapsid protein (N) gene. Phylogenetic analysis of the sequences identified viruses from lineages II and IV only. The analysis also indicated a shared origin of the viruses from Niger with PPRVs from neighbouring countries suggesting transboundary movement.