Zika virus (ZIKV) drew worldwide attention when a recent epidemic was linked to fetal microcephaly. Here we used human embryonic stem cell derived trophoblasts as a model for primitive placental trophoblast to test the hypothesis that there are differences in how the two genetically distinct ZIKV lineages, African (AF) and Asian (AS), target the human placenta. Upon infection with three AF (ib-H30656, SEN/1984/41525-DAK, and MR-766) and three AS (FSS13025, MexI-44, and PANcdc259249) ZIKV strains, we observed that severe placental cell lysis was only induced after infection with AF strains, while viral replication rates remained similar between both lineages. Differences in cytopathic effects (CPE) were not observed in Vero cells, indicating that the AF strains were not inherently superior at cell lysis. Taken together, we propose that infection with AF strains of ZIKV early in pregnancy would likely result in pregnancy loss, rather than allow further fetal development with accompanying brain damage. Our results also suggest that the long term laboratory-adapted MR-766 strain does not behave aberrantly in cell culture relative to other AF lineage strains.

SARS-CoV-2 is the causative agent of COVID-19 and responsible for the current global pandemic. We and others have previously demonstrated that cats are susceptible to SARS-CoV-2 infection and can efficiently transmit the virus to naïve cats. Here, we address whether cats previously exposed to SARS-CoV-2 can be re-infected with SARS-CoV-2. In two independent studies, SARS-CoV-2-infected cats were re-challenged with SARS-CoV-2 at 21 days post primary challenge (DPC) and necropsies performed at 4, 7 and 14 days post-secondary challenge (DP2C). Sentinels were co-mingled with the re-challenged cats at 1 DP2C. Clinical signs were recorded, and nasal, oropharyngeal, and rectal swabs, blood, and serum were collected and tissues examined for histologic lesions. Viral RNA was transiently shed via the nasal, oropharyngeal and rectal cavities of the re-challenged cats. Viral RNA was detected in various tissues of re-challenged cats euthanized at 4 DP2C, mainly in the upper respiratory tract and lymphoid tissues, but less frequently and at lower levels in the lower respiratory tract when compared to primary SARS-CoV-2 challenged cats at 4 DPC. Viral RNA and antigen detected in the respiratory tract of the primary SARS-CoV-2 infected cats at early DPCs were absent in the re-challenged cats. Naïve sentinels co-housed with the re-challenged cats did not shed virus or seroconvert. Together, our results indicate that cats previously infected with SARS-CoV-2 can be experimentally re-infected with SARS-CoV-2; however, the levels of virus shed was insufficient for transmission to co-housed naïve sentinels. We conclude that SARS-CoV-2 infection in cats induces immune responses that provide partial, non-sterilizing immune protection against re-infection.

The transmission cycle of chikungunya virus (CHIKV) requires that mosquito vectors get persistently infected with the virus, following its oral acqsuisition from a vertebrate host. The mosquito midgut is the initial organ that gets infected with orally acquired CHIKV. Following its replication in the midgut epithelium, the virus exits the midgut and infects secondary tissues including the salivary glands before being transmitted to another host. Here, we investigate the pattern of CHIKV dissemination from the midgut of Aedes aegypti at the ultrastructural level. Bloodmeal ingestion caused overstretching of the midgut basal lamina (BL), which was disrupted in areas adjacent to muscles surrounding the midgut as shown by scanning electron microscopy (SEM). Using both transmission electron microscopy (TEM) and focused ion beam scanning electron microscopy (FIB-SEM) to analyze midgut preparations, mature chikungunya (CHIK) virions were found accumulating at the BL and within strands of the BL at 24–32 h post-infectious bloodmeal (pibm). From 48 h pibm onwards, virions no longer congregated at the BL and became dispersed throughout the basal labyrinth of the epithelial cells. Ingestion of a subsequent, non-infectious bloodmeal caused mature virions to congregate again at the midgut BL. Our study suggests that CHIKV needs a single replication cycle in the midgut epithelium before mature virions directly traverse the midgut BL during a relatively narrow time window, within 48 h pibm.

Epizootic hemorrhagic disease virus (EHDV) is an arthropod-transmitted RNA virus and the causative agent of epizootic hemorrhagic disease (EHD) in wild and domestic ruminants. In North America, white-tailed deer (WTD) experience the highest EHD-related morbidity and mortality, although clinical disease is reported in cattle during severe epizootics. No commercially licensed EHDV vaccine is available in North America. The objective of this study was to develop and evaluate a subunit vaccine candidate to control EHD in WTD. Recombinant VP2 (rVP2) outer capsid proteins of EHDV serotypes 2 (EHDV-2) and 6 (EHDV-6) were produced in a baculovirus-expression system. Mice and cattle vaccinated with EHDV-2 or EHDV-6 rVP2 produced homologous virus-neutralizing antibodies. In an immunogenicity/efficacy study, captive-bred WTD received 2 doses of EHDV-2 rVP2 or sham vaccine, then were challenged with wild-type EHDV-2 at 30 d post vaccination. None of the rVP2-vaccinated deer developed clinical disease, no viral RNA was detected in their blood or tissues (liver, lung, spleen, kidney), and no EHDV-induced lesions were observed. Sham-vaccinated deer developed clinical disease with viremia and typical EHD vascular lesions. Here, we demonstrate a rVP2 subunit vaccine that can provide protective immunity from EHDV infection and which may serve as an effective tool in preventing clinical EHD and reducing virus transmission.

African swine fever (ASF) is an infectious viral disease caused by African swine fever virus (ASFV), that causes high mortality in domestic swine and wild boar (Sus scrofa). Currently, outbreaks are mitigated through strict quarantine measures and the culling of affected herds, resulting in massive economic losses to the global pork industry. In 2019, an ASFV outbreak was reported in Mongolia, describing a rapidly progressing clinical disease and gross lesions consistent with the acute form of ASF; the virus was identified as a genotype II virus. Due to the limited information on clinical disease and viral dynamics within hosts available from field observations of the Mongolian isolates, we conducted the present study to further evaluate the progression of clinical disease, virulence, and pathology of an ASFV Mongolia/2019 field isolate (ASFV-MNG19), by experimental infection of domestic pigs. Intramuscular inoculation of domestic pigs with ASFV-MNG19 resulted in clinical signs and viremia at 3 days post challenge (DPC). Clinical disease rapidly progressed, resulting in the humane euthanasia of all pigs by 7 DPC. ASFV-MNG19 infected pigs had viremic titers of 10⁸ TCID₅₀/mL by 5 DPC and shed virus in oral secretions late in disease, as determined from oropharyngeal swabs. Whole-genome sequencing confirmed that the ASFV-MNG19 strain used in this study was a genotype II strain highly similar to other regional strains. In conclusion, we demonstrate that ASFV-MNG19 is a virulent genotype II ASFV strain that causes acute ASF in domestic swine.

For efficient cell entry and membrane fusion, SARS-CoV-2 spike (S) protein needs to be cleaved at two different sites, S1/S2 and S2’ by different cellular proteases such as furin and TMPRSS2. Polymorphisms in the S protein can affect cleavage, viral transmission, and pathogenesis. Here, we investigated the role of arising S polymorphisms in vitro and in vivo to understand the emergence of SARS-CoV-2 variants. First, we showed that the S:655Y is selected after in vivo replication in the mink model. This mutation is present in the Gamma Variant Of Concern (VOC) but it also occurred sporadically in early SARS-CoV-2 human isolates. To better understand the impact of this polymorphism, we analyzed the in vitro properties of a panel of SARS-CoV-2 isolates containing S:655Y in different lineage backgrounds. Results demonstrated that this mutation enhances viral replication and spike protein cleavage. Viral competition experiments using hamsters infected with WA1 and WA1-655Y isolates showed that the variant with 655Y became dominant in both direct infected and direct contact animals. Finally, we investigated the cleavage efficiency and fusogenic properties of the spike protein of selected VOCs containing different mutations in their spike proteins. Results showed that all VOCs have evolved to acquire an increased spike cleavage and fusogenic capacity despite having different sets of mutations in the S protein. Our study demonstrates that the S:655Y is an important adaptative mutation that increases viral cell entry, transmission, and host susceptibility. Moreover, SARS-COV-2 VOCs showed a convergent evolution that promotes the S protein processing.