In a recent study published on the bioRxiv* preprint server, researchers conducted a longitudinal study to examine neutralizing antibody kinetics in naturally occurring acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected white-tailed deer severe (WTD) population for about 16 months.
Study: Persistence of SARS-CoV-2 neutralizing antibodies over 13 months in captive and naturally infected white-tailed deer (Odocoileus virginianus), Texas. Image credit: Tony Campbell/Shutterstock
background
Wild WTD, Odocoileus virginianus, has the potential to be a natural reservoir of SARS-CoV-2. However, how long natural infection persists in WTD is unknown, and the precise duration of persistence of neutralizing antibodies in this species is also unknown. In WTD species found in the Midwestern states and Texas in the United States (US), studies have documented SARS-CoV-2 seroprevalence of ~30–40%. Experimental studies have also shown that WTD lung cells are permissive to SARS-CoV-2 infection. Therefore, they transmit the virus vertically and by contact.
Field investigations have frequently reported human-to-WTD transmission events, followed by deer-to-deer SARS-CoV-2 transmission. Studies detected several SARS-CoV-2 lineages in the WTD that have not infected humans, raising concerns about zoonotic spillover to humans and the emergence of new SARS-CoV-2 variants. In one of their previous studies, the researchers sampled 36 WTDs from a deer facility in central Texas in September 2021. More than 90% of these samples were seropositive for SARS-CoV-2, twice as much as wild-type WTD. The confined environment of this deer facility facilitated the transmission of SARS-CoV-2.
About the study
In the present study, researchers used archived serum samples from 21 WTDs from the same deer facility in Texas to determine the time of their initial exposure to SARS-CoV-2 and the duration of antibody persistence in these animals. In particular, the team collected a blood sample and a swab sample on March 4, 2022 for the current prospective study.
They tested swab samples from the test animals using quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) that amplifies the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) gene. Similarly, the team tested for the presence of SARS-CoV-2 in blood samples using plaque reduction neutralization tests (PRNT90) at seven time points between November 9, 2020, and March 4, 2020. 2022.
Results of the study
PRNT90 results showed that all 21 WTD females from the captive cervid facility in central Texas were seropositive in January 2021. This confirmed that SARS-CoV-2 infection and subsequent seroconversion occurred between December 16, 2020 and January 27, 2021 in these animals. More than 90% of these animals had detectable neutralizing antibodies to SARS-CoV-2, indicating that anti-SARS-CoV-2 antibodies in these animals persisted for at least 13 months.
The researchers observed a gradual decrease in the geometric mean of endpoint PRNT90 titers, from 299.6 in January 2021 to 254 in March 2021. The subsequent rate of decline in PRNT90 titers was rapid and reached a from 66.5 in July 2021. Again, the decrease rate slowed down to 46.2 in September 2021 and 36.7 in March 2022. In particular, Deer-10 had an increase of four times in PRNT90 titles between January and March 2021.
Conclusions
Data from the study indicate that WTD is a key species for a sustainable enzootic transmission cycle of SARS-CoV-2. All 21 deer became seropositive on January 27, 2021, indicating the occurrence of an initial single exposure event rather than multiple exposure events over time. Furthermore, neutralizing antibodies persisted for at least 402 days in this naturally infected WTD population. The authors later observed a continuous decrease in neutralizing antibody titers over 13 months. However, consistent with previous reports, RT-qPCR results from respiratory and rectal swabs from all deer were negative between September 2021 and March 2022.
The current data extend previous estimates based on experimental infection studies. Studies have not quantified the threshold of protective neutralizing antibody titers for SARS-CoV-2 in WTD. Therefore, high end-value titers do not need to protect against reinfection in deer, although the study findings showed that neutralizing antibodies persisted for 13 months in the WTD. In addition, Deer-006 and Deer-011 had a temporary four- to eightfold increase in neutralizing antibody titers during the study period. Thus, like vaccinated humans, sequential exposures to SARS-CoV-2 resulted in anamnestic responses in deer. It should be noted that anamnestic responses confound the rate of neutralizing antibody decay in some cases.
In conclusion, the findings of the study strengthen the understanding of the natural kinetics of infection in WTD. Future research should determine whether anti-SARS-CoV-2 neutralizing antibodies in WTD can prevent further infection and viral transmission by infected WTD, given that these species, which are abundant in nature, have the unique potential to serve as animal hosts for SARS-CoV-2.
*Important news
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.
Journal reference:
- Sarah Anne Hamer, Chase M Nunez, Christopher Roundy, Wendy Tang, Logan F Thomas, Jack J Richison III, Jamie Benn, Lisa Auckland, Terry Hensley, Walter E Cook, Alex Pauvolid-Correa, Gabriel Hamer. (2022). Persistence of neutralizing antibodies to SARS-CoV-2 over 13 months in naturally infected captive white-tailed deer (Odocoileus virginianus), Texas. bioRxiv. doi: