In a recent research letter published in Emerging Infectious Diseases, researchers evaluated antibodies targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in cattle from farms in Germany.
Since SARS-CoV-2, the causative agent of coronavirus disease 2019 (COVID-19) in humans, was initially discovered in late 2019, it has spread incredibly quickly globally. This massive worldwide pandemic has claimed more than 6.3 million human lives in roughly 2.5 years of virus circulation.
SARS-CoV-2 infection in humans increases the possibility of animal transmission. With a particular focus on discovering vulnerable species and prospective reservoirs or intermediate hosts, various researchers evaluated the involvement of wildlife and livestock species at the human-animal interface since the COVID-19 pandemic's inception.
According to prior reports, several animal species, including nonhuman primates, canids, felids, mustelids, white-tailed deer, and numerous Cricetidae rodent species, were susceptible to SARS-CoV-2 infection in experimental conditions, whereas swine or poultry were not. Following experimental SARS-CoV-2 inoculation, domestic ruminants like sheep, cattle, or goats had poor susceptibility; very few animals could contract the infection without animal-to-animal spread.
Furthermore, in only one to two days, cattle tested SARS-CoV-2-positive by reverse transcription polymerase chain reaction (rt-PCR) following experimental infection. Thus, serologic screening may be more valuable for detecting priorly infected animals and determining the spillover infection rates in the field.
About the study
In the present research, the scientists serologically examined 1,000 samples of cattle gathered in Germany at the end of 2021 to determine the COVID-19 risk to cattle.
In detail, the team evaluated 1,000 plasma or serum samples obtained from cattle at 83 farms in four German federal states (Lower Saxony, Bavaria, Thuringia, and Saxony-Anhalt). They noted that no permissions were required to obtain these specimens because they were surplus material from standard diagnostic submissions made by the accountable veterinarians in the framework of the health surveillance of the specific cattle farm.
Sampling took place in the 2021 autumn and the early winter of 2021 to 2022, when a massive surge of SARS-CoV-2 infections attributed to the Delta variant of concern (VOC) occurred among humans. The researchers investigated two to 20 randomly chosen plasma or serum samples per farm. They sampled farm 31 twice, and the owner of the animals was quarantined in the interim.
A multispecies enzyme-linked immunosorbent assay (ELISA) based on the SARS-CoV-2 receptor-binding domain (RBD) was used to evaluate all samples from cattle. The authors analyzed an extra 100 randomly procured cattle control samples from 2016 in Germany.
The study results showed that 11 cattle from nine farms were positive for the SARS-CoV-2 RBD ELISA among the 2021 cattle samples; one of these animals, from farm 31, was sampled after the quarantine of the owner. An indirect immunofluorescence test using Vero cells infected with the SARS-CoV-2 2019 nCoV Muc-IMB-1 strain as the antigen matrix confirmed positive results of ELISA for all but one sample from farm 8. Besides, titers varied from 1:8 to 1:512, with farm 31's seropositive animal having the highest titer.
The assessment of RBD-ELISA-positive 11 samples utilizing a surrogate virus neutralization test (sVNT) enabled the identification of SARS-CoV-2 neutralizing antibodies. The analysis was accomplished by simulating the interplay between the receptor protein of the host cell membrane, i.e., angiotensin-converting enzyme 2 (ACE2) and SARS-CoV-2. Moreover, four cattle from farms 74, 47, 31, and 11 had positive sVNT results.
According to the study findings, 11 cattle samples from Germany were positive for SARS-CoV-2 antibodies, implying that cattle may occasionally become virus-infected and seroconvert through exposure to COVID-19-infected keepers. Yet, the team found no additional evidence of intraspecies viral spread in the field, in line with the former experimental infection assessments.
However, the authors noted that future monitoring initiatives should include cattle farms, particularly given that another CoV (i.e., BCoV) was quite common across cattle, and a BCoV infection did not shield against contracting SARS-CoV-2 according to a prior study. Further, animal hosts' vulnerability to the Omicron VOC was unknown. Furthermore, recombination events between the two viruses could result from double infections in a single animal, a process seen with other CoVs.
The limited susceptibility of cattle to SARS-CoV-2 makes emergence extremely unlikely, but a potential chimera among SARS-CoV-2 and BCoV could pose an extra concern. The study stated that ruminants should be considered in outbreak studies and warranted routine testings to prevent the spread of novel SARS-CoV-2 variants across the livestock population.