Infektion des Pferdes mit Equinem Coronavirus (ECoV)
Infection of horses with Equine Coronavirus (ECoV)
Thein P
DOI: 10.21836/PEM20200507
Jahr: 2020
Volume: 36
Ausgabe: 5
Seiten: 438–444
Coronaviruses are part of our biozoenosis since we exist. Their different biological properties are part of their evolutionary strategies like the change of host systems, pathogenicity, organotropism, antigenicity, immunogenicity. Beside man and domesticated animals a wide range of susceptible animal host systems is existing. Because of the different antigenic relationships coronaviruses have been divided into former group1 and group2. The new taxonomy now divides these viruses into genuses alpha- and betacoronaviruses (man and animals) and gammacoronaviruses (poultry). The first isolation of typical coronavirus particles were found by electron microscopy in fecal samples from foals in Kentucky. They died or were killed in the acute stage of gastroenteritis, described by Bass and Sharpee in 1974. Neutralizing antibodies against calf diarrhoe coronavirus were identified in equine sera. In New Zealand Durham et al. (1979) investigated foals with profuse watery diarrhea and detected coronavirus in their feces. They described a wide range of ages in the infected animals and serological crossreaction with calf coronavirus. More virus-positive cases of enteric foal disease have been reported within the following years. Eugster and Jones (1988) reported on coronavirus in an aborted equine fetus, Ward et al. (1983) described the presence of coronavirus in foals with diarrhea. Sato et al. (1981) demonstrated neutralizing antibodies to calf diarrhoe coronavirus also in horses in Japan. All these reports are dealing with cases of severe gastroenteritis and foal diarrhea. The first coronavirus associated diarrhea in mature horses has been documented by Huang et al. (1983). In summer 1982 there were 113 clinical cases of an acute form of diarrhea in Maryland/U.S.A.. The isolated virus was not related to bovine coronavirus, swine transmissible gastroenteritis or avian infectious bronchitis on the base of fluorescent antibody tests. Coronavirus could be isolated not only from feces but also from plasma samples of the sick horses. The classically virological diagnostic techniques have been now replaced by molecular tests using the qPCR. About since 1990 reports on disease associated with Equine coronavirus infections mainly in mature horses in the U.S.A. are based on qPCR positive feces. The description of the clinical signs, virus transmission and diagnosis of the ECoV – disease could be summarized as follows. ECoV is spread via oral investigation of qPCR positive feces, fecal –oral transmission can also occur when horses make oral contact with surfaces or objects that have contaminated with infected feces. Coronavirus is most commonly diagnosed in winter. Carrier status, subclinical infected horses (11-93%) can spread ECoV. This belongs to foals as well as adult horses. Incubation in 2-4 days, clinical signs fever up to 40, 5°C, anorexia, depression, sometimes colic, diarrhea may or may not be present, frequently laying down. Low white blood cell count (leucopenia, lymphopenia) hyperammonemia could be responsible with signs of encephalopathic disease. Fecal virus load (ECoV genome equivalents per gram of feces) might be of prognostic value in affected horses. Prognosis is good in most cases. Exposure to the virus can result in up to 85% infection rate, most horses do not show clinical signs. An horse with fever and no respiratory clinical signs may have ECoV in the feces. Therefore the qPCR of their feces is recommended. Epidemiogical studies of ECoV infections are still limited. Seroprevalence could be investigated by an indirect enzyme- linked immunosorbent assay (ELISA) utilizing ECoV spike S1 protein since 2017. Using this test Zhao et al. (2019) demonstrated seroconversion by analyzing 27 paired sera from horses involved in an ECoV outbreak. From 1084 sera from healthy Dutch horses seropositivy carried from 25, 9% (young horses) to 82, 8% (adult horses). Sera of Icelandic horses reacted positive to 62, 09%. This ELISA demonstrated the surprisingly high percentage of seropositive European horses. Seroprevalence in 9, 6% of 5247 Sera of healthy horses from different geographic regions of the U.S. were demonstrated by Kooijman et al. in 2017. Summarizing the available results ECoV could be demonstrated to high percentages in fecal material but also in nasal secretions (Pusterla et al., 2019) and plasma and blood (Huang et al., 1982, Goodrich et al., 2020) from healthy and/or diseased horses. Therefore it seems to be questionable whether fecal- oral transmission may be the only way of infection chains. Further investigations are necessary. This belongs also to the recommended methods of prevention. They are based on high standards of sanitation in all equine facilities, disinfection methods etc.. Isolation of horses for 3 weeks, esp. horses with fever and no evidence of respiratory illness, horses moving to new facilities esp. in cases where horses moved from a facility with ECoV – positive feces test are part of the recommendations.