Three lineages (BA.1, BA.2 and BA.3) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant of concern predominantly drove South Africa’s fourth Coronavirus Disease 2019 (COVID-19) wave. We have now identified two new lineages, BA.4 and BA.5, responsible for a fifth wave of infections. The spike proteins of BA.4 and BA.5 are identical, and similar to BA.2 except for the addition of 69–70 deletion (present in the Alpha variant and the BA.1 lineage), L452R (present in the Delta variant), F486V and the wild-type amino acid at Q493. The two lineages differ only outside of the spike region. The 69–70 deletion in spike allows these lineages to be identified by the proxy marker of S-gene target failure, on the background of variants not possessing this feature. BA.4 and BA.5 have rapidly replaced BA.2, reaching more than 50% of sequenced cases in South Africa by the first week of April 2022. Using a multinomial logistic regression model, we estimated growth advantages for BA.4 and BA.5 of 0.08 (95% confidence interval (CI): 0.08–0.09) and 0.10 (95% CI: 0.09–0.11) per day, respectively, over BA.2 in South Africa. The continued discovery of genetically diverse Omicron lineages points to the hypothesis that a discrete reservoir, such as human chronic infections and/or animal hosts, is potentially contributing to further evolution and dispersal of the virus.

West Nile virus (WNV), a mosquito-borne flavivirus, is endemic to South Africa. However, its contribution to acute febrile and neurological disease in hospitalized patients in South Africa is unknown. This study examined two patient cohorts for WNV using molecular testing and IgM serology with confirmation of serological results by viral neutralization tests (VNT) to address this knowledge gap. Univariate analysis was performed using collected demographic and clinical information to identify risk factors. In the first cohort, 219 cerebrospinal fluid (CSF) specimens from patients with acute neurological disease in Gauteng hospitals collected in January to June 2017 were tested for WNV. The study identified WNV in 8/219 (3.65%, 95.00% CI (1.59–7.07)) patients with unsolved neurological infections. The second cohort, from 2019 to 2021, included 441 patients enrolled between January and June with acute febrile or neurological disease from urban and rural sites in Gauteng and Mpumalanga provinces. West Nile virus was diagnosed in 40/441 (9.07%, 95.00% CI (6.73–12.12)) of patients, of which 29/40 (72.50%, 95.00% CI (56.11–85.40)) had neurological signs, including headaches, encephalitis, meningitis, and acute flaccid paralysis (AFP). Notably, most of the cases were identified in children although adolescents and senior adults had a significantly higher risk of testing WNV positive. This suggests a previously underestimated disease burden and that WNV might be underrecognized as a cause of febrile and neurological diseases in hospitalized patients in South Africa, especially in children. This emphasizes the importance of further research and awareness regarding arboviruses of public health concern.

West Nile and Banzi Viruses, South Africa

Mosquito Vectors for Shuni Virus, South Africa

Viruses in the Orthobunyavirus genus, Peribunyaviridae family, are associated with encephalitis, birth defects and fatalities in animals, and some are zoonotic. Molecular diagnostic investigations of animals with neurological signs previously identified Shuni virus (SHUV) as the most significant orthobunyavirus in South Africa (SA). To determine if other orthobunyaviruses occur in SA, we screened clinical specimens from animals with neurological signs, abortions, and acute deaths from across SA in 2021 using a small (S) segment Simbu serogroup specific TaqMan real-time reverse transcription polymerase chain reaction (RT-PCR). Positive cases were subjected to Sanger sequencing and phylogenetic analysis to identify specific viruses involved, followed by next-generation sequencing (NGS) and additional PCR assays targeting the medium (M) segment and the large (L) segment. In total, 3/172 (1.7%) animals were PCR positive for Simbu serogroup viruses, including two horses with neurological signs and one aborted goat fetus in 2021. Phylogenetic analyses confirmed that the two horses were infected with SHUV strains with nucleotide pairwise (p-) distances of 98.1% and 97.6% to previously identified strains, while the aborted goat fetus was infected with a virus closely related to Shamonda virus (SHAV) with nucleotide p-distances between 94.7% and 91.8%. Virus isolation was unsuccessful, likely due to low levels of infectious particles. However, phylogenetic analyses of a larger fragment of the S segment obtained through NGS and partial sequences of the M and L segments obtained through RT-PCR and Sanger sequencing confirmed that the virus is likely SHAV with nucleotide p-distances between 96.6% and 97.8%. This is the first detection of SHAV in an aborted animal in SA and suggests that SHAV should be considered in differential diagnosis for abortion in animals in Southern Africa.

The prevalence and distribution of African alphaviruses such as chikungunya have increased in recent years. Therefore, a better understanding of the local distribution of alphaviruses in vectors across the African continent is important. Here, entomological surveillance was performed from 2014 to 2018 at selected sites in north-eastern parts of South Africa where alphaviruses have been identified during outbreaks in humans and animals in the past. Mosquitoes were collected using a net, CDC-light, and BG-traps. An alphavirus genus-specific nested RT-PCR was used for screening, and positive pools were confirmed by sequencing and phylogenetic analysis. We collected 64,603 mosquitoes from 11 genera, of which 39,035 females were tested. Overall, 1462 mosquito pools were tested, of which 21 were positive for alphaviruses. Sindbis (61.9%, N = 13) and Middelburg (28.6%, N = 6) viruses were the most prevalent. Ndumu virus was detected in two pools (9.5%, N = 2). No chikungunya positive pools were identified. Arboviral activity was concentrated in peri-urban, rural, and conservation areas. A range of Culicidae species, including Culex univittatus, Cx. pipiens s.l., Aedes durbanensis, and the Ae. dentatus group, were identified as potential vectors. These findings confirm the active circulation and distribution of alphaviruses in regions where human or animal infections were identified in South Africa.