The geographical distribution and diversity of viruses can differ between cultivated areas and adjacent natural environments, raising questions about the interplay between plant diversity and the species richness and prevalence of the phytoviruses. As both the amplification and the dilution of viral species richness due to increasing host diversity have been theorized and observed, a deeper understanding of how plant-viruses interact in natural environments is needed to explore how host availability conditions viral diversity and distributions. This study explores interactions of viruses from the Mastrevirus genus (family Geminiviridae) with hosts from the Poaceae family across ten sites from three contrasting ecosystems on La Réunion. Among 273 plant pools, representing 61 Poales species, 15 Mastrevirus species were characterized from 22 hosts. We find a strong association of mastreviruses with hosts from agro-ecosystems and the absence of mastreviruses in subalpine areas, dominated by native plants. This suggests that all detected mastreviruses likely originated from viruses introduced through agricultural activities rather than being native to La Réunion. Analyses of the structure of the host plant-mastrevirus interaction network revealed a pattern of increasing viral richness with increasing host richness. Accounting for variations in the diversity of hosts across sites, we observed increasing viral niche occupancies with increasing host species richness. Virus realized richness at any given site is conditioned on the global capacity of the plant populations to host diverse mastreviruses. Whether this tendency is driven by synergy between viruses, or by an interplay between vector population and plant richness, remains to be established.

Background: In Angola, COVID-19 cases have been reported in all provinces, resulting in >105,000 cases and >1,900 deaths. However, no detailed genomic surveillance into the introduction and spread of the SARS-CoV-2 virus has been conducted in Angola. We aimed to investigate the emergence, and epidemic progression during the peak of the COVID-19 pandemic in Angola. Methods: We generated 1,210 whole-genome SARS-CoV-2 sequences, contributing West African data to the global context, that were phylogenetically compared against global strains. Viral movement events were inferred using ancestral state reconstruction. Results: The epidemic in Angola was marked by four distinct waves of infection, dominated by 12 viral lineages, including VOCs, VOIs, and the VUM C.16, which was unique to Southwestern Africa and circulated for an extended period within the region. Viral exchanges occurred between Angola and its neighboring countries, and strong links with Brazil and Portugal reflected the historical and cultural ties shared between these countries. The first case likely originated from southern Africa. Conclusion: A lack of a robust genome surveillance network and strong dependence on out-of-country sequencing limit real-time data generation to achieve timely disease outbreak responses, which remains of the utmost importance to mitigate future disease outbreaks in Angola.