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OBJECTIVE: To investigate the distribution and risk factors of hepatitis delta virus (HDV) infection in Cameroon. DESIGN: We tested for hepatitis B virus (HBV) surface antigen (HBsAg) and anti-HDV antibody 14 150 samples collected during a survey whose participants were representative of the Cameroonian adult population. The samples had already been tested for hepatitis C virus and HIV antibodies. RESULTS: Overall, 1621/14 150 (weighted prevalence=11.9%) participants were HBsAg positive, among whom 224/1621 (10.6%) were anti-HDV positive. In 2011, the estimated numbers of HBsAg positive and HDV seropositives were 1 160 799 and 122 910 in the 15-49 years age group, respectively. There were substantial regional variations in prevalence of chronic HBV infection, but even more so for HDV (from 1% to 54%). In multivariable analysis, HDV seropositivity was independently associated with living with an HDV-seropositive person (OR=8.80; 95% CI: 3.23 to 24.0), being HIV infected (OR=2.82; 95% CI: 1.32 to 6.02) and living in the South (latitude <4°N) while having rural/outdoor work (OR=15.2; 95% CI: 8.35 to 27.6, when compared with living on latitude ≥4°N and not having rural/outdoor work). CONCLUSION: We found evidence for effective intra-household transmission of HDV in Cameroon. We also identified large differences in prevalence between regions, with cases concentrated in forested areas close to the Equator, as described in other tropical areas. The reasons underlying these geographical variations in HDV prevalence deserve further investigation.

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This article draws on Charles Rosenberg's classic essay "What Is an Epidemic?" (1989) to reflect on the complex narrative structures and temporalities of epidemics as they are experienced and storied. We begin with an analysis of Rosenberg's use of Albert Camus's The Plague and a discussion of how epidemics have been modeled in literature and in epidemiology concomitantly. Then, we argue that Charles Rosenberg's characterization of epidemics as events bounded in time that display narrative and epidemiological purity fails to account for the reinvention of life within health crises. Adopting the ecological, archaeological, and anthropological perspectives developed within African studies enriches the range of available plots, roles, and temporal sequences and ultimately transforms our way of depicting epidemics. Instead of events oriented toward their own closure, epidemics might be approached as unsettling, seemingly endless periods during which life has to be recomposed.

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This article is a history of the field station Lamto, in Ivory Coast, which was created by French ecologists in 1962, after independence. It retraces the origins, the logics and the contradictions of an extraordinarily ambitious scientific project, which aimed at the systematic, holistic, quantitative and multi-disciplinary description of a unit of African nature - the savannah ecosystem. It explores how knowledge-making was articulated with work hierarchies and postcolonial politics, lifestyles, values and affects. It reconstitutes the political ecology of a research station in ecology, following in its residences, laboratories and open-air experiments the co-production of domesticity, nature, science and (post-)colonial situations.

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Unlike the pandemic form of HIV-1 (group M), group O viruses are endemic in west central Africa, especially in Cameroon. However, little is known about group O's genetic evolution, and why this highly divergent lineage has not become pandemic. Using a unique and large set of group O sequences from samples collected from 1987 to 2012, we find that this lineage has evolved in successive slow and fast phases of diversification, with a most recent common ancestor estimated to have existed around 1930 (1914-1944). The most rapid periods of diversification occurred in the 1950s and in the 1980s, and could be linked to favourable epidemiological contexts in Cameroon. Group O genetic diversity reflects this two-phase evolution, with two distinct populations potentially having different viral properties. The currently predominant viral population emerged in the 1980s, from an ancient population which had first developed in the 1950s, and is characterized by higher growth and evolutionary rates, and the natural presence of the Y181C resistance mutation, thought to confer a phenotypic advantage. Our findings show that although this evolutionary pattern is specific to HIV-1 group O, it paralleled the early spread of HIV-1 group M in the Democratic Republic of Congo. Both viral lineages are likely to have benefited from similar epidemiological contexts. The relative role of virological and social factors in the distinct epidemic histories of HIV-1 group O and M needs to be reassessed.

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It has recently been suggested that HCV genotype 2 (HCV-2) was more recently introduced to Cameroon (Middle Africa) than West African countries. In order to explore the relationships among HCV-2 strains from Cameroon and West Africa, and to estimate the epidemic history of each lineage, a recently-developed Bayesian evolutionary analysis approach was used. The estimated date of the most recent common ancestor (MRCA) of the Cameroon HCV-2 strains, 1630 (95% highest posterior density interval: 1470-1760) was slightly more recent than that of West Africa, 1540 (95% highest posterior density interval: 1380-1680). Estimates of epidemic history indicate significant differences between the two strains. HCV-2 appears to have spread relatively slowly within the West African population from 1630 to 1900, whilst the Cameroon lineages exhibit rapid, exponential spread from 1920 to 1960. This comparative genetic analysis indicates that Cameroon HCV-2 strains are derived from West African strains and that HCV-2 has undergone radically different epidemiological histories in the two regions.

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Hepatitis C virus (HCV) infection in Cameroon is characterized by widespread seropositivity and great virus genetic diversity (3 genotypes and over 10 subtypes). A total of 244 HCV NS5B sequences of 382-405 bp long (95 type 1, 58 type 2, and 91 type 4) were phylogenetically analyzed to estimate the history of the HCV epidemic in Cameroon. The newly developed Bayesian coalescent approach was used to infer the history of each HCV type. The estimated dates of the most recent common ancestors (MRCA) for genotypes 1 (1500; 95% confidence interval (95% CI): 1300-1650) and 4 (1500; 95% CI: 1350-1700) were in the same range, while the date for genotype 2 MRCA (1600; 95% CI: 1400-1750) was slightly more recent. The mean genetic distance between HCV genotype 1 sequences was greater than that of HCV type 4 sequences, itself greater than that of HCV type 2 sequences. The initial infected populations of all three genotypes did not grow until recently, when they grew exponentially. The growth rate has now begun to slow, with a less steep exponential growth curve. The period of exponential growth of all the three genotypes was between 1920 and 1960. These results (i) confirm that HCV genotypes 1 and 4 have produced long-term endemics, (ii) suggest that genotype 2 was introduced into Cameroon more recently, and (iii) indicate that the exponential spread of the three genotypes between 1920 and 1960 coincided with the mass campaign against trypanosomiasis and mass vaccinations in Cameroon.

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A hepatitis C virus (HCV) serological study conducted in 2003 on 1,434 individuals in Yaounde and other HCV seroepidemiological studies on 2,066 sera sampled between 1993 and 1997 in four geographically distinct rural areas (Ntem, Mekas, Yokadouma, and Nditam) in Cameroon, are described. Two patterns of HCV seroprevalence were observed. The first pattern, represented by Nditam and Yokadouma populations, showed low HCV seroprevalence rates (2.9% and 3.3%, respectively) increasing moderately with age (9.0% and 16.7% after age 50). The second pattern showed high seroprevalence rates (6.9% for Yaounde, 14.4% and 16.7% for Ntem and Mekas, respectively). These rates increased dramatically with age (32.8%-49.5% after age 50). The age-specific anti-HCV prevalence curve of the 1993 Mekas survey paralleled those of the 1997 Ntem and 2003 Yaounde surveys. Using the year of birth as the x-axis, the three curves closely matched each other. This clearly indicates a cohort effect for which the seroprevalence trends are clearly related with the year of birth, rather than the age. The highest prevalence was observed among people born around 1940.

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The nucleus accumbens core (AcbC), anterior cingulate cortex (ACC), and central nucleus of the amygdala (CeA) are required for normal acquisition of tasks based on stimulus-reward associations. However, it is not known whether they are involved purely in the learning process or are required for behavioral expression of a learned response. Rats were trained preoperatively on a Pavlovian autoshaping task in which pairing a visual conditioned stimulus (CS+) with food causes subjects to approach the CS+ while not approaching an unpaired stimulus (CS-). Subjects then received lesions of the AcbC, ACC, or CeA before being retested. AcbC lesions severely impaired performance; lesioned subjects approached the CS+ significantly less often than controls, failing to discriminate between the CS+ and CS-. ACC lesions also impaired performance but did not abolish discrimination entirely. CeA lesions had no effect on performance. Thus, the CeA is required for learning, but not expression, of a conditioned approach response, implying that it makes a specific contribution to the learning of stimulus-reward associations.

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