Disentangling the role of Africa in the global spread of H5 highly pathogenic avian influenza.

The role of Africa in the dynamics of the global spread of a zoonotic and economically-important virus, such as the highly pathogenic avian influenza (HPAI) H5Nx of the Gs/GD lineage, remains unexplored. Here we characterise the spatiotemporal patterns of virus diffusion during three HPAI H5Nx intercontinental epidemic waves and demonstrate that Africa mainly acted as an ecological sink of the HPAI H5Nx viruses. A joint analysis of host dynamics and continuous spatial diffusion indicates that poultry trade as well as wild bird migrations have contributed to the virus spreading into Africa, with West Africa acting as a crucial hotspot for virus introduction and dissemination into the continent. We demonstrate varying paths of avian influenza incursions into Africa as well as virus spread within Africa over time, which reveal that virus expansion is a complex phenomenon, shaped by an intricate interplay between avian host ecology, virus characteristics and environmental variables.

Highly Pathogenic Avian Influenza A(H5N8) Virus, Cameroon, 2017.

Highly pathogenic avian influenza A(H5N8) viruses of clade 2.3.4.4 spread into West Africa in late 2016 during the autumn bird migration. Genetic characterization of the complete genome of these viruses detected in wild and domestic birds in Cameroon in January 2017 demonstrated the occurrence of multiple virus introductions.

Effect of vaccination on cattle subclinically infected with foot-and-mouth disease virus in Cameroon.

Foot-and-mouth disease (FMD) is one of the most contagious and economically important livestock diseases worldwide. Four serotypes of FMD virus (FMDV; O, A, SAT1, SAT2) circulate in Cameroon, and a trivalent inactivated vaccine against the three most common serotypes (O, A, SAT2) was recently introduced in 2014. The objective of this study was to characterize vaccine performance in cattle under natural hyperendemic conditions in the Adamawa region of Cameroon. Vaccinated cattle (n = 50) and non-vaccinated controls (n = 100) were monitored by serum and oropharyngeal fluid (OPF) sample collection through a 12-month period. Anti-FMDV non-structural protein (anti-NSP) seroprevalence increased from 59.3% (89/150) at the beginning of the study to 85.8% (103/120) at the end of the study, and FMDV RNA was found in 28% (42/150) of animals overall, despite detection of clinical signs of FMD in only 6 non-vaccinated animals. Viral sequence analysis indicated that subclinical infections of FMDV serotypes O and A were present within the study herds during the study period, which was reflected by an overall increase of anti-NSP seroprevalence during the study. There was no association between vaccination status and seroconversion or prevalence of FMDV RNA in OPF. Younger cattle had higher odds of detection of FMDV RNA in OPF, but older animals were more likely to be seropositive. This study suggests vaccination of herds previously exposed to FMDV may help to limit clinical signs and reduce economic losses caused by FMDV. These findings also suggest that subclinical circulation of FMDV occurs in hyperendemic regions regardless of vaccination.

Serotype-Specific Transmission and Waning Immunity of Endemic Foot-and-Mouth Disease Virus in Cameroon.

Foot-and-mouth disease virus (FMDV) causes morbidity and mortality in a range of animals and threatens local economies by acting as a barrier to international trade. The outbreak in the United Kingdom in 2001 that cost billions to control highlighted the risk that the pathogen poses to agriculture. In response, several mathematical models have been developed to parameterize and predict both transmission dynamics and optimal disease control. However, a lack of understanding of the multi-strain etiology prevents characterization of multi-strain dynamics. Here, we use data from FMDV serology in an endemic setting to probe strain-specific transmission and immunodynamics. Five serotypes of FMDV affect cattle in the Far North Region of Cameroon. We fit both catalytic and reverse catalytic models to serological data to estimate the force of infection and the rate of waning immunity, and to detect periods of sustained transmission. For serotypes SAT2, SAT3, and type A, a model assuming life-long immunity fit better. For serotypes SAT1 and type O, the better-fit model suggests that immunity may wane over time. Our analysis further indicates that type O has the greatest force of infection and the longest duration of immunity. Estimates for the force of infection were time-varying and indicated that serotypes SAT1 and O displayed endemic dynamics, serotype A displayed epidemic dynamics, and SAT2 and SAT3 did not sustain local chains of transmission. Since these results were obtained from the same population at the same time, they highlight important differences in transmission specific to each serotype. They also show that immunity wanes at rates specific to each serotype, which influences patterns of local persistence. Overall, this work shows that viral serotypes can differ significantly in their epidemiological and immunological characteristics. Patterns and processes that drive transmission in endemic settings must consider complex viral dynamics for accurate representation and interpretation.