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Equids are susceptible to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) based on the high homology to the ACE-2 receptor; however, only silent infection has been documented now.
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Equine coronavirus (ECoV) infection in adult equids is often characterized by unspecific clinical signs such as fever, lethargy, and anorexia, whereas changes in fecal character and colic are infrequently observed in infected animals.
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A diagnosis of ECoV should be considered when multiple adult horses are affected by fever, lethargy, anorexia with or without gastrointestinal signs and hematological changes (leukopenia due to neutropenia and/or lymphopenia) are consistent with an underlying viral disease. A laboratory diagnosis of ECoV is supported by the molecular detection of ECoV in feces.
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ECoV infection is often self-limiting requiring at best supportive treatment with non-steroidal antiinflammatory drugs and polyionic fluids and antimicrobials if endotoxemia/septicemia is suspected.
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The prevention of ECoV infection should focus on the implementation of routine management practices aimed at reducing the likelihood of introducing and disseminating ECoV at any horse-based premise as well as the timely isolation of horses with suspected ECoV infection.
Severe acute respiratory syndrome coronavirus 2
Although successful experimental transmission of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has been documented in a variety of domestic and laboratory animal species, including dogs, cats, ferrets, pigs, New Zealand white rabbits, mice, and Syrian hamsters,
Animals and SARS-CoV-2: Species susceptibility and viral transmission in experimental and natural conditions, and the potential implications for community transmission.
Detection of SARS-CoV-2 in pets living with COVID-19 owners diagnosed during the COVID-19 lockdown in Spain: A case of an asymptomatic cat with SARS-CoV-2 in Europe.
Less research has been focusing on characterizing the role of equids in the COVID-19 pandemic. Susceptibility of equids (horses and donkeys) has been established by comparative analysis of ACE-2 protein sequences, and the data showed that equids have low affinity to bind.
A recent functional and genetic study determined that viral receptor ACE-2 orthologs from 44 different species, including horses, were able to bind SARS-CoV-2 spike protein, therefore supporting viral entry.
Experimental intranasal infection with an ancestral SARS-CoV-2 strain (virus strain 2019-nCoV/USA-WA1/2020) in a single horse has been reported in the literature (Table 1).
The attempt to experimentally infect the single horse failed, which is not surprising, considering that experimental infections of equids using the closely related Middle East respiratory syndrome coronavirus (MERS-CoV) showed lack of immune response and no viral RNA detected in respiratory secretions.
However, one must keep in mind that SARS-CoV-2 has continued to evolve and adapt, meaning that, it is possible that more contemporary human-adapted variants will show greater potential to replicate in equids.
Table 1Studies documenting the susceptibility of equids to severe acute respiratory syndrome coronavirus-2
Study Type
Equid (Number)
Outcome
References
Experimental infection
Horse (1)
No molecular detection of SARS-CoV-2 in nasal secretions and feces and no virus isolation from respiratory tissues
Serological survey of SARS-CoV-2 for experimental, domestic, companion and wild animals excludes intermediate hosts of 35 different species of animals.
Molecular detection of SARS-CoV-2 in nasal secretions and/or feces of healthy horses and horses with acute onset of fever and respiratory signs has remained unsuccessful.
Although molecular detection of SARS-CoV-2 in respiratory secretions is limited to a short shedding period, especially in silent shedders, serology is more sensitive at capturing past-exposure. A recent serologic survey from China did not find antibodies specific to SARS-CoV-2 from healthy horses.
Serological survey of SARS-CoV-2 for experimental, domestic, companion and wild animals excludes intermediate hosts of 35 different species of animals.
This was in sharp contrast to a study evaluating silent transmission of SARS-CoV-2 between racetrack workers with asymptomatic COVID-19 and racing thoroughbred horses.
This study detected specific antibodies to SARS-CoV-2 in 35/587 (5.9%) racing horses. Current CDC guidelines recommend that owners with SARS-CoV-2 avoid any close contact with their animals, including equids. A recent study documented seroconversion in one of 2 horses with direct contact to an individual (horse owner) with clinical COVID-19.
None of the 2 horses had detectable SARS-CoV-2 in nasal secretions, blood, and feces.
Although horses are apparently susceptible to SARS-CoV-2 and are likely to become infected through spillover from COVID-19 individuals, horses are unlikely to contribute to the spread of SARS-CoV-2. However, it is important to continue to monitor possible human-to-horse transmission, especially with the emergence of highly transmissible SARS-CoV-2 variants,
and to recommend that COVID-19 individuals avoid close contact with companion animals (dogs, cats, ferrets, horses).
Equine coronavirus
Cause
Coronaviruses are single-stranded, positive-sense, nonsegmented, enveloped RNA viruses responsible for organ-specific syndromes in a variety of mammalian and avian species.
The family Coronaviridae is subdivided in 2 subfamilies, Torovirinae and Coronavirinae, with the latter subfamily containing 4 genera defined by serologic cross-reactivity and genetic differences: Alphacoronavirus, Betacoronavirus, Deltacoronavirus, and Gammacoronavirus.
Discovery of seven novel mammalian and avian coronaviruses in the genus deltacoronavirus supports bat coronaviruses as the gene source of alphacoronavirus and betacoronavirus and avian coronaviruses as the gene source of Gammacoronavirus and Deltacoronavirus.
Equine coronavirus (ECoV) belongs to the Embecovirus subgenera and is phylogenetically related to bovine coronavirus (BCoV), human OC43 and HKU1 coronaviruses, canine respiratory coronavirus, mouse hepatitis virus and sialodacryoadenitis virus coronavirus OC43, and porcine hemagglutinating encephalomyelitis virus. SARS-CoV-2 belongs to the Sarbecovirus subgenera, whereas MERS-CoV belongs to the Merbecovirus subgenera.
Partial and complete genome sequences from a small number of ECoV isolates from Japan, the United States, and Europe has shown high level of sequence homology ranging between 97.2% and 99.6%.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
The genetic database will likely expand in the next few years as more isolates are been sequenced. This information is important in order to understand the virus at the molecular level, determine possible virulence factors, and help develop future diagnostic and preventive tools.
Epidemiology
Unfortunately, little is known about the epidemiology of ECoV, as most studies have focused on individual outbreak reports. Until the early 2010s, ECoV was considered one of many enteric pathogens associated with foal diarrhea. ECoV was first recognized as an enteric pathogen of adult horses by Oue and collaborators.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Available demographic information has been retrieved from diagnostic laboratories showing that the overall number of ECoV positive fecal samples by quantitative PCR (qPCR) has gradually increased since the introduction of the testing in 2012 (Real-time PCR Research and Diagnostics Core Facility, University of California, Davis, USA). The increasing frequency of qPCR-positive feces likely relates to greater awareness and testing availability. It is interesting to notice that submissions from ECoV qPCR-positive cases originate from all the lower 48 states of the United States. There is also an apparent seasonality to ECoV qPCR-positive cases with a higher detection rate during the colder months of the year (Fig. 1),
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Fig. 1Monthly distribution of ECoV qPCR-positive fecal samples among all fecal samples submitted to a private diagnostic laboratory in the United States. The data encompasses the time frame from January 2012 to May 2022.
Outbreaks and individual cases of ECoV in adult horses have predominantly been reported in racing, pleasure, and show horses, and less frequently in breeding stocks. Although age-susceptibility has been recognized for many animal and human coronaviruses, one hypothesis for the apparent low frequency of clinical ECoV cases in breeding equids is that ECoV is more likely to circulate between susceptible young and adult equids at breeding farms, leading to continuous silent exposure and protection against clinical disease. However, observational exceptions are always present with biological processes and ECoV is no exception. There is one case report on an ECoV outbreak at a large American miniature horse-breeding farm with 17% of breeding animals showing clinical disease.
Prevalence factors associated with seropositivity to ECoV have been studied on 5247 healthy adult horses originating from 18 states in the United States (Table 2).
A total of 504/5247 horses (9.6%) was tested seropositive to ECoV using an S1-based enzyme-linked immunosorbent assay (ELISA). Geographic origin (Midwestern regions), breed (draft breed), and use (ranch/farm use, breeding use) displayed the highest odds ratio of seroprevalence. Although breed predisposition to ECoV infection has not been determined, it is interesting to note that the initial and subsequent outbreaks from Japan all occurred in racing draft horses.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Another study evaluated the risk of exposure to ECoV in 333 apparently healthy horses from 29 farms throughout Israel using an S1-based ELISA (see Table 2).
A total of 41 out of 333 horses (12.3%) were seropositive. The ECoV seropositive horses originated from 17/29 farms (58.6%), and the seroprevalence per farm ranged from 0% to 37.5%. The only factor found to be significantly associated with ECoV exposure in the multivariable model was the geographic area, with a higher seroprevalence in horses residing in central Israel than in horses from the north or south. Longitudinal epidemiologic studies are greatly needed in order to better understand and define risk factors associated with ECoV infection in adult equids.
Table 2Seroprevalence and risk factors for equine coronavirus documented in populations of healthy adult horses in the United States and Israel
Population
Seroprevalence
Country
Risk Factors
References
Healthy horses (n = 5247)
9.6%
United States
Midwestern regions (P = .008) Draft horse breed (P = .003) Ranch/farm use (P = .034) Breeding use (P = .016)
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Fatalities are rare but have been associated with disruption of the gastrointestinal mucosal barrier leading to septicemia, endotoxemia, and hyperammonemia-associated encephalopathy.
The predominant clinical signs associated with ECoV in adult horses are nonspecific and include anorexia, lethargy, and fever (≥38.6°C; Fig. 2, Table 3).
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Although ECoV is an enteric virus, changes in fecal character (diarrhea to soft formed feces) and/or colic are not consistently observed, findings that often challenge equine practitioners into including ECoV as a differential diagnosis. Horses with ECoV infection can sometimes develop acute neurologic signs consistent with encephalopathy and are characterized by severe lethargy, head pressing, ataxia, proprioceptive deficits, recumbency, nystagmus, and seizures.
Fig. 2Compilation of clinical signs observed from 101 adult horses with clinical ECoV infection (Pusterla, personal communication). Fever was defined as a rectal temperature ≥38.6°C. Neurologic signs were consistent with encephalopathy and included aimless wandering, circling, head pressing, recumbence, and seizure.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
One must keep in mind that most ECoV infections presenting to equine veterinarians may be mild and often self-limiting, requiring minimal to no medical care. However, horses with marked to severe systemic signs are often referred to equine veterinary hospitals and the severity of clinical disease may easily mimic other gastrointestinal diseases. In a retrospective case series of 33 adult horses testing qPCR-positive for ECoV in feces, the presenting complaints were fever (83%), anorexia (47%), and colic (43%).
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
When the hospitalized horses with qPCR-positive ECoV feces were compared with a cohort of horses with fever and/or loose manure that tested qPCR-negative for ECoV infection, presenting complaints were similar.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Another study compared clinical features of ECoV infection with enteric salmonellosis and found that the clinical signs of fever and colic were similar between the 2 groups.
Although most clinical ECoV infections are associated with outbreaks, some present as individual cases. A recent retrospective case series, including 5 horses with ECoV infection that were not associated with an outbreak, reported that anorexia and fever were observed in all horses and that 4 of 5 horses had moderate-to-severe diarrhea.
Patients were hospitalized for a median of 5 days and all survived to discharge. Collectively, the various case series using hospitalized horses have shown that clinical signs were not specific for ECoV and often similar to other enteric infectious diseases. However, the outcome of ECoV is favorable with the majority of the hospitalized horses surviving to discharge.
Experimental studies have shown that young and adult horses can successfully become infected with ECoV through the feco-oral route.
Because of the difficulty of growing ECoV in vitro, all experimental challenges used feces from naturally infected animals. Collectively, these studies have shown that most infected horses develop mild and self-limiting clinical signs consistent with anorexia, fever, and changes in fecal character (Table 4). Blood tests showed leukopenia and/or lymphopenia in approximately 50% of the infected horses, which is consistent with hematological changes observed in naturally occurring cases of ECoV infection. ECoV was detected in the feces of all experimentally infected horse via qPCR, and nasal secretions and whole blood tested occasionally qPCR-positive for ECoV. While a qPCR-positive blood sample is consistent with viremia, it could not be determined if qPCR-positive nasal secretions were due to nasal replication and shedding of the virus, from environmental contamination from the feces, or from both sources. Although experimental infections with ECoV have only been attempted in a small number of horses, it seems that clinical disease, although mild, can be consistently reproduced, making the model suitable to study the pathogenesis and the immunity of ECoV.
Table 4Studies documenting clinical, hematological and laboratory findings associated with experimental equine coronavirus infection in young and adult horses
Population (Number of Horses)
Clinical Signs
Blood Work
Molecular Testing
Serology
References
9–10-month-old draft horses (3)
Fever (2), anorexia (2), pasty feces (2)
Leukopenia/lymphopenia (1), elevated SAA (2)
ECoV RNA in feces (3), nasal secretions (3), and blood (2)
Diagnosing ECoV infection can be challenging, especially in horses lacking specific enteric signs. The diagnosis can be supported by the presence of neutropenia and/or lymphopenia and the detection of ECoV in feces.
Hematological findings of ECoV infections are generally consistent with a viral hemogram characterized by leukopenia due to neutropenia and/or lymphopenia. In a review of 35 cell blood counts from horses with natural ECoV infection supported through qPCR detection of coronavirus in feces, 74% of diseased horsed showed leukopenia, 66% neutrophilia, and 72% lymphopenia (Fig. 3). It is, however, important to keep in mind that approximately 10% of horses with ECoV infection display an unremarkable hemogram. Hematological abnormalities are expected to resolve within 5 to 7 days as long as no complications associated with the disruption of the gastrointestinal barrier occur. Less consistent hematological abnormalities can include the presence of band neutrophils, monocytosis and leukocytosis due to neutrophilia and monocytosis during the recovery period. When 8 clinical cases of ECoV infection were compared with 12 horses with enteric salmonellosis, neutrophil count was decreased in both groups but was not significantly different.
Further, in a case series of 33 horses with ECoV infection seen at a veterinary hospital, ECoV qPCR-positive horses had lower white blood cells (range 680–16,200/μL, median 3000/μL), neutrophil counts (150–14,400/μL, median 1250/μL), and lymphocyte counts (420–3470/μL, median 860/μL) when compared with ECoV qPCR-negative horses.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Fig. 3White blood cell, neutrophil, and lymphocyte count of 35 adult horses with suspected ECoV infection. The results are expressed as individual values. Median values are represented by horizontal bars. Red brackets represent normal reference ranges for each cellular fraction displayed (WBC 5000–11,600/μL; neutrophil count 2600–6800/μL; lymphocyte count 1600–5800 μL).
Serum biochemistry profiles may be unremarkable; however, abnormalities in ECoV-infected horses have been reported and include electrolyte derangements, hyperbilirubinemia, hyperglycemia, hyperlipidemia, hypoproteinemia, increased muscle enzymes, and azotemia.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
ECoV infection with concurrent signs of encephalopathy has been linked to hyperammonemia. A recent ECoV case series reported on 1 horse with severe hyperammonemia (677 μmol/L; reference interval ≤60 μmol/L) with encephalopathic signs that subsequently died.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Hyperammonemia associated with ECoV infection is likely due to increased ammonia production within or absorption from the gastrointestinal tract due to gastrointestinal barrier breakdown. An increase in enteric ammonia production could also be the result of bacterial microbiome changes associated with ECoV infection.
It is only in recent years that the diagnostics for ECoV have markedly improved with the use of qPCR. The limitation of historic detection modalities, such as negative stain electron microscopy (EM) or antigen-capture ELISA, is that they are not sensitive enough when viral particles are not present in sufficient numbers. The biological sample of choice to support an ECoV diagnosis is feces or rectal swabs. Previous work has shown that molecular assays are rapid, cost-effective, sensitive, and specific for ECoV.
Unfortunately, no study has compared the various molecular techniques (qPCR vs RT loop-mediated isothermal amplification) and their superior sensitivity to negative stain EM or antigen-capture ELISA. Although the detection of ECoV in the feces of diseased horses is highly suggestive of infection, one must keep in mind that 4% to 83% of horses can remain subclinically infected during an ECoV outbreak.
Viral kinetics of ECoV in feces from experimentally infected horses have shown that horses begin to shed detectable ECoV RNA in their feces at 3 or 4 days postinfection and continue shedding virus until 12 or 14 days postinfection.
Peak ECoV shedding is consistently seen on day 3 to 4 following the development of clinical disease (Fig. 4). Average length of ECoV RNA detection following onset of natural infection ranges from 3 to 9 days, however, naturally infected horses have been shown to sporadically shed ECoV RNA in feces up to 98 days.
Although additional biological samples such as whole blood (viremia) and nasal secretions (shedding) have tested qPCR-positive for ECoV in experimentally
occurring infections, these sample types do not consistently test positive and should not be used to support a diagnosis of ECoV infection. The molecular detection of ECoV can be challenging, especially during peracute disease when diseased horses experience gastrointestinal stasis due to colic and/or there are not enough viral particles in the feces to be detected. Recommendations are to repeat testing of fecal matter in a suspected index case at a later time point or collect multiple samples for pooled testing. Further, it has been the author’s experience that ECoV-infected horses presenting with systemic clinical signs such as fever, lethargy, and anorexia are more likely to be tested for respiratory pathogens through respiratory secretions than enteric pathogens through feces. In order to speed up diagnostic turn-around-time, one should consider submitting both, nasal secretions and feces, in adult horses with acute onset of systemic signs in order to test for selected respiratory and enteric pathogens or stage the testing to the more likely cause. This process will speed up the analysis because additional samples (ie, feces) have already been shipped to the laboratory and are available for ECoV testing.
Fig. 4Diagram showing temporal clinical signs and fecal shedding of ECoV in an adult horse presented to a referring hospital because of anorexia, lethargy, and fever.
Serology has been established and validated for ECoV and is available in research laboratories mostly to document seroconversion in experimentally infected horses or study the epidemiology of ECoV in various horse populations.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Serology can be used to retrospectively establish recent infection using acute and convalescent serum samples and documenting either seroconversion or increase in serum titers.
Necropsy cases of suspected enteritis should have feces or gastrointestinal content tested by qPCR for ECoV and other gastrointestinal infectious agents. Further, formalin-fixed intestinal tissue samples can also be tested by immunochemistry and direct fluorescent antibody testing using BCoV reagents.
Following an incubation period of 48 to 72 hours, most horses infected with ECoV develop a self-limiting enteritis, which generally resolves with minimal supportive care. In most clinical adult horses, ECoV is the only pathogen detected in the feces of affected horses, suggesting a unique pathogenicity.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Gross and histologic findings were consistent with severe diffuse necrotizing enteritis, characterized by marked villus attenuation, epithelial cell necrosis in the tips of the villi, neutrophilic and fibrin extravasation into the small intestinal lumen, as well as crypt necrosis, microthrombosis, and hemorrhage. In these 3 necropsied cases, ECoV was detected by qPCR in intestinal tissue, gastrointestinal content, and/or feces. Further, coronavirus antigen was detected by immunohistochemistry and/or direct fluorescent antibody testing in the small intestine of all cases. In comparison to BCoV, there is no evidence that ECoV has respiratory tropism based on the lack of respiratory signs in affected equids and histologic changes in horses undergoing necropsy.
The lack of respiratory tropism is supported by a recent experimental study, which showed that in only 1 out of 4 horses, ECoV was detected in the lungs by qPCR but not by in situ hybridization.
In the case series reporting on the pathologic condition of ECoV infection in 3 naturally infected equids, one of them displayed hyperammonemic encephalopathy with Alzheimer type II astrocytosis throughout the cerebral cortex, suggesting a strong association between ECoV necrotizing enteritis, hyperammonemia and the development of encephalopathy.
Most horses with clinical ECoV infection recover in a few days with little supportive to no treatment at all. Horses showing persistent elevated rectal temperature affecting their appetite and attitude have been treated with antipyretic (dipyrone at 30 mg/kg body weight [BWT] q12–24 hours intravenous [IV]) or anti-inflammatory drugs (flunixin meglumine [0.5–1.1 mg/kg BWT q12–24 hours IV or per os [PO]; phenylbutazone [2–4 mg/kg BWT q12–24 hours IV or PO]; firocoxib [0.1 mg/kg BWT q24 hours PO or 0.09 mg/kg BWT q24 hours IV]) for 24 to 48 hours, as long as they stay hydrated. Horses with colic, persistent anorexia, and/or diarrhea have been treated more intensively with fluid and electrolytes per nasogastric intubation or intravenous administration of polyionic fluids until clinical signs have resolved. Additionally, antimicrobials and gastrointestinal protectants should be considered in horses developing signs of endotoxemia and/or septicemia secondary to disruption of the gastrointestinal barrier. Horses with suspected or documented hyperammonemia should be treated with oral lactulose (0.1–0.2 mL/kg BWT q6-q12 hours PO), neomycin sulfate (4–8 mg/kg BWT q8 hours PO), or fecal transfaunation and crystalloid fluids.
Immunity and Immunoprophylaxis
Less is known about the immune responses and immune protection against ECoV. For the closely-related BCoV, serum levels of neutralizing and HI antibody from naturally infected calves and cattle arriving at feedlots have been shown to correlate with protection against both, enteric and respiratory disease.
Epidemiologic factors and isotype-specific antibody responses in serum and mucosal secretions of dairy calves with bovine coronavirus respiratory tract and enteric tract infections.
Infectivity-neutralizing and hemagglutinin-inhibiting antibody responses to respiratory coronavirus infections of cattle in pathogenesis of shipping fever pneumonia.
Antibody responses of cattle with respiratory coronavirus infections during pathogenesis of shipping fever pneumonia are lower with antigens of enteric strains than with those of a respiratory strain.
Further, cattle that recovered from winter dysentery after experimental infection with BCoV maintained a very long-lasting BCoV-specific serum (IgA and IgG) and local (IgA) antibody response.
It will need to be determined if certain levels of antibodies and what type of specific immune response correlates with protection against ECoV.
Immunization strategies have been best described in cattle for the prevention of winter dysentery infection using commercially available BCoV vaccines. Due to the close genetic homology of ECoV with BCoV, serologic responses to BCoV vaccines have recently been investigated in horses. One study used a killed-adjuvanted BCoV vaccine in 6 healthy yearling horses and reported a measurable serologic response in all horses following the administration of 2 vaccines given 28 days apart.
A second study investigated the safety, humoral response, and viral shedding in horses inoculated either orally, intranasally, or intrarectally with a commercially available modified-live BCoV vaccine.
The results of that study showed that the modified-live BCoV was safe to administer to horses through various routes, caused minimal virus shedding and resulted in detectable antibodies to BCoV in 27% of the vaccinates. Collectively, these 2 BCoV vaccines, while showing measurable antibody responses to BCoV, cannot be recommended at the present time due to the lack of efficacy data.
Control Strategies
The cornerstone of ECoV prevention resides in strict biosecurity measures aimed at reducing the risk of introducing and disseminating ECoV on equine premises. It is important to be vigilant when working-up horses presenting with fever, anorexia, and lethargy, with or without concurrent enteric signs. Such horses should be isolated until ECoV, as well as other potential infectious pathogens, have been ruled in or out. ECoV qPCR-positive horses should be isolated and stable-mates or herd-mates closely monitored until the outcome of past-exposure has been determined. Outbreaks of ECoV are generally short lasting, especially when strict biosecurity measures have been followed, and quarantine can routinely be lifted 2 to 3 weeks following the resolution of clinical signs in the last affected horse.
Coronaviruses are susceptible to heat, detergents, and disinfectants such as sodium hypochlorite, povidone iodine, 70% ethanol, glutaraldehyde, quaternary ammonium compounds, phenolic compounds, formaldehyde, peroxymonosulfate, and accelerated hydrogen peroxide.
Moreover, coronaviruses have been reported to survive well at low temperatures and high relative humidity. Their survival on surfaces is also long, up to 120 hours and even longer in organic medium such as feces, urine, and wastewater.
As incidental hosts, horses are unlikely to contribute to the spread of SARS-CoV-2. Rare infections of SARS-CoV-2 have been reported in equids, thought to occur secondary to the spillover of SARS-CoV-2 from symptomatic or asymptomatic COVID-19 individuals. ECoV has emerged as an enteric pathogen of adult horses in recent years and has been reported in Japan, Europe, and the United States. There are increasing reports of the disease, arising from increased awareness in the field and the availability of diagnostic tests for detecting ECoV in feces of affected horses. Clinical presentation of ECoV infection is often limited to systemic signs such as fever, lethargy, and anorexia, although enteric signs are present in less than 20% of infected cases. Although blood tests may suggest a viral infection (lymphopenia and neutropenia), laboratory diagnosis is supported by the detection of ECoV in feces using qPCR. ECoV infection is often self-limiting, requiring little to no supportive treatment. Although no vaccine is available now, prevention of ECoV infection is best achieved through routine management practices aimed at reducing the likelihood of introducing and disseminating ECoV at any horse-based premise as well as the timely isolation of horses with suspected clinical ECoV infection.
Clinics care points
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Equids are deadend hosts to SARS-CoV-2 and do not contribute to the COVID-19 pandemic.
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ECoV often causes only systemic clincial signs in adult horses.
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ECoV is diagnosed via the molecular detection of ECoV in feces.
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ECoV is often a self-limiting disease requiring little to no medical treatment.
Disclosure
The author has nothing to disclose.
References
Jo W.K.
de Oliveira-Filho E.F.
Rasche A.
et al.
Potential zoonotic sources of SARS-CoV-2 infections.
Animals and SARS-CoV-2: Species susceptibility and viral transmission in experimental and natural conditions, and the potential implications for community transmission.
Detection of SARS-CoV-2 in pets living with COVID-19 owners diagnosed during the COVID-19 lockdown in Spain: A case of an asymptomatic cat with SARS-CoV-2 in Europe.
Serological survey of SARS-CoV-2 for experimental, domestic, companion and wild animals excludes intermediate hosts of 35 different species of animals.
Discovery of seven novel mammalian and avian coronaviruses in the genus deltacoronavirus supports bat coronaviruses as the gene source of alphacoronavirus and betacoronavirus and avian coronaviruses as the gene source of Gammacoronavirus and Deltacoronavirus.
Isolation of an equine coronavirus from adult horses with pyrogenic and enteric disease and its antigenic and genomic characterization in comparison with the NC99 strain.
Clinical presentation, diagnostic findings, and outcome of adult horses with equine coronavirus infection at a veterinary teaching hospital: 33 cases (2012-2018).
Epidemiologic factors and isotype-specific antibody responses in serum and mucosal secretions of dairy calves with bovine coronavirus respiratory tract and enteric tract infections.
Infectivity-neutralizing and hemagglutinin-inhibiting antibody responses to respiratory coronavirus infections of cattle in pathogenesis of shipping fever pneumonia.
Antibody responses of cattle with respiratory coronavirus infections during pathogenesis of shipping fever pneumonia are lower with antigens of enteric strains than with those of a respiratory strain.
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