Potential spread of Covid-19 from a woman to her horse is described in the study

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Researchers have described a possible spread of the Covid-19 virus from a woman to one of her horses in California, and suggested infected people avoid horses and other pets as a precaution.

Laboratory tests showed that the Quarter horse’s immune system responded with an antibody to the virus. The animal did not show signs of disease.

Nicola Posterla and her fellow researchers conclude that the findings suggest that horses can be silently infected with SARS-CoV-2 after close contact with infected humans.

“As a precaution, humans infected with SARS-CoV-2 should avoid close contact with horses and other companion animals during their illness to prevent transmission of the virus.”

The researchers write in the journal VirusesDescribe the circumstances surrounding the case.

In October 2021, a middle-aged woman developed fever, fatigue, muscle aches and loss of smell. Soon, she tested positive for Covid-19 via a rapid antigen test (RAT).

Infection was confirmed by laboratory tests, with genotyping results consistent with the temporally circulating Delta B.1.617.2 variant.

Prior to the onset of clinical symptoms, the woman was caring for two quarter horses, aged between 8 and 21 years. Her daily two-hour routine included feeding twice a day, cleaning and grooming stalls, and exercising.

Because the woman was concerned that her horses might be exposed to the virus, Pusterla was contacted in order to monitor the horses.

Animals were monitored daily with routine physical assessment. In addition, blood, nasal secretions and stool were collected weekly for three weeks after the woman was diagnosed with Covid-19. The different samples were tested in a laboratory for the Corona virus.

The researchers reported that both horses remained healthy throughout the three-week observation period.

However, serum testing in younger horses showed an antibody response to the virus seven days after the owner tested positive. Peak antibody levels were reached 21 days after diagnosis.

Additional blood samples were collected from the affected horse for 60 days after diagnosis, with antibody levels rising until the last sample collection.

“Despite the poor sensitivity of horses to SARS-CoV-2 and little evidence of natural infection, the current case report describes a possible spread from a Covid-19 patient to one of her horses,” the researchers said.

Various companion animal species such as dogs and cats showed little expression of the disease, despite being susceptible to SARS-CoV-2. “It is clear that horses follow the same pattern after infection with SARS-CoV-2,” they said.

This observation is further supported by the inability to detect SARS-CoV-2 by quantitative reverse transcriptase polymerase chain (RT-qPCR) assay in 667 horses with fever and respiratory signs in a previously reported study.

In fact, none of the horses in the current study returned a positive RT-qPCR test for the virus.

“The lack of detection of SARS-CoV-2 via RT-qPCR in the seroconverted horse is likely related to the short elimination period and weekly sample collection interval,” they said.

“A similar pattern involving seroconversion with very short virality and nasal shedding was recently reported in dogs and pigs, which is associated with reduced susceptibility of these animal species to SARS-CoV-2.”

They continued, “While many host, viral and environmental factors can predispose to infection, it was interesting to note that only the youngest of the two horses were mutated to SARS-CoV-2.

“While the number of affected horses is too low for any age-related association to be identified, it is interesting to note that younger cats appear to be more susceptible than older cats.”

The authors emphasized that without the discovery and characterization of SARS-CoV-2 from the horse, the source of infection remains speculative. However, the conditions indicate direct human-to-animal transmission.

They note that while a previous attempt to experimentally infect a single horse with SARS-CoV-2 failed, it is possible that some human-adapted variants reproduced in equids.

They said it would be interesting to determine whether newer variants, such as omicron, which is known to increase the rate of transmission of the virus, are more likely to cause silent infections in equids.

The antibody response observed in a young quarter-horse mare, compared to the more susceptible animal species, was low.

This observation likely reflects a short infection stage, supported by the lack of clinical disease and the absence of detectable virus. However, the antibody response persisted during the entire study period. ”

The study team noted that antibodies to the virus have been shown to persist for up to 10 months in some dogs and cats from Covid-19-positive households.

“Currently and based on the limited scientific data available, the overall risk of transmission of SARS-CoV-2 between humans with Covid-19 and equines appears to be low,” they wrote.

However, it is important to continue to study the impact of potential ramifications with longer studies aimed at sampling horses at regular intervals once caregivers or horse owners have been diagnosed with Covid-19.

“It is essential to determine the ability of SARS-CoV-2 to infect and evolve in different types of animals such as horses, particularly in light of the potential for animal-to-human transmission.

“Although there is no evidence of horse-to-horse transmission of SARS-CoV-2, current guidelines recommend owners who are infected with SARS-CoV-2 avoid any close contact with their animals, including horses.”

The study team consists of Pusterla, Antoine Chaillon, Caroline Ignacio, Davey Smith, Samantha Barnum, Kaila Lawton, Greg Smith and Bradley Pickering. Pusterla, Barnum, and Lawton with the Department of Medicine and Epidemiology at the College of Veterinary Medicine at the University of California, Davis; Chailon, Ignacio, and Smith work in the Department of Infectious Diseases and Global Public Health at the University of California, San Diego; While Smith and Pickering work with the National Center for Foreign Animal Diseases, part of the Canadian Food Inspection Agency.

Pusterla, N.; Shilon, A.; Ignatius, C.; Smith, D.M.; Barnum, S.; Lawton, Coy Smith, G.; Pickering, b. SARS-CoV-2 Seroconversion in an adult horse with direct contact with a COVID-19 individual. Viruses 2022, 14, 1047. https://doi.org/10.3390/v14051047

The study published under CC licensecan be read here.

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