Enterovirus E

Formerly known as

Bovine enterovirus (BEV);

Also known as

Enteric cytopathic bovine orphan virus (ECBO).

Description

Enterovirus E is a picornavirus of the genus Enterovirus. This virus is endemic in cattle populations worldwide, and although it is normally fairly nonpathogenic, it sometimes causes reproductive, respiratory, or intestinal disease, particularly when an animal is infected with another pathogen at the same time.

Enterovirus E is spread by either the oral-fecal route (ingesting feed or water contaminated by feces containing the virus) or by the respiratory route. Viral shedding may occur for several months after the animal experiences the initial infection. This virus has not been shown to transmit from animals to humans.

BEVs were originally classified into seven serotypes, but now divided into just two serotypes which are further classified into subtypes. Serotype 1 is found in many animals, including cattle, sheep and humans. Serotype 2 viruses are only found in domestic cattle.

Because of some similarities with the virus that causes foot and mouth disease (FMD), careful differentiation is required for diagnosis.

Most cattle show no clinical signs when infected with this virus, but abortion, stillbirth, infertility, and mortality in newborn animals can occur following infection of the reproductive tract. Intestinal infection may cause diarrhea and weight loss. Respiratory infection can produce a thick nasal discharge.

Signs

• Abortion,
• Diarrhea,
• Weight loss,
• Nasal discharge

Cause

Clinical signs are fairly nonspecific. Since bovine enterovirus is always present in cattle populations, other causes of disease must be ruled out before diagnosing enterovirus as the cause of disease. There are several laboratory tests that can identify this virus in tissues or body secretions.

More than 600 BEV isolates have been found in healthy as well as sick cattle, so they are actually not a very common cause of disease. Some have been shown to be pathogenic, but it is difficult to produce disease in cattle experimentally, even though these isolates have been found in severe clinical cases in the absence of other detectable causative agents. Most isolates, however, tend to be relatively harmless in cattle.

On the other hand, some isolates have been found in animals suffering from inflammation of the testicles, diarrhea in newborns, abortion, and winter dysentery.

Most picornaviruses are host specific except for the encephalomyelitis viruses isolated from over 30 host species, and the aphthoviruses that infect at least 200 species of mammals. BEV belonging to serotype 1 have been isolated from domestic cattle, water buffalo, sheep, goats, Sika deer, dogs, wild African buffalo and impala. The viruses belonging to serotype 2 have only been isolated from domestic cattle, however.

All ages and breeds of domestic cattle are susceptible.

Most enteroviruses, including bovine enterovirus (BEV), invade the body by the oral route and result in colonization of the alimentary tract. Most BEV infections in cattle, like enterovirus infections in humans, are subclinical. Clinically affected cattle can have widespread replication in many organs in addition to local lymph nodes, and then show reproductive, respiratory and intestinal signs of disease.

It is difficult to diagnose bovine enterovirus (BEV) infection clinically because there are generally no clinical signs. In cattle with gastrointestinal, respiratory and reproductive signs, other agents causing gastrointestinal, respiratory and reproductive diseases must be ruled out.

Acute infections are associated with diverse clinical signs in some herds, but usually the infections are not recognized. After recovery from acute infection, especially from calf diarrhea and winter dysentery, clinically-normal cattle shed viruses. Virus shedding following recovery can occur for more than a year. The pathogenic relationship among healthy carrier, acute infection, and persistent infection after recovery is not understood.

Bovine enterovirus (BEV)-infected cattle shed the virus continually through feces and nasal discharge for more than three months (sometimes up to 15 months) after recovery from clinical signs. The virus is highly resistant to environmental stresses, so it may persist in the environment and spread to neighboring herds.

Following an outbreak of diarrhea in a dairy herd, for instance, BEV can be transmitted rapidly to neighboring herds, and is associated with up to a 70% reduction of milk production.

Studies in Spain have shown that BEV is widespread, with the virus less prevalent in cattle from extensive farms where the animals are spread out (69% of cattle carrying the virus) than in cattle from intensive farms where cattle are closely confined (94% of the cattle carrying the virus). Analysis of samples collected from a farm in the U.S. indicated that the virus was present in the spring in 2 to 4-month-old calves but that the calves cleared the infection by summer.

Recently, it has been shown that infectious virus particles are present in water from animal watering tanks, pastures, and streams/rivers in regions where the virus is endemic, demonstrating its ability to survive in watery environments. Interest in these viruses has increased in recent years, since they can be utilized as markers for fecal contamination of the environment.

Bovine enterovirus isolates from the U.S. have been recovered from diverse sources that included feces of normal calves, as well as sick cattle with various clinical problems. Some BEVs have been isolated from calves and pregnant cows with coughs, fever, clear or mucous nasal discharge, mild intestinal infections, or mild shipping fever.

One BEV strain has been isolated from abdominal fluid, stomach contents, and allantoic fluid (the fluid surrounding a fetus) of an aborted fetus. Other BEV strains were isolated from cows with pinkeye and from a dairy herd with a history of pinkeye. More than 20 BEV isolates from South Korea were obtained from fecal samples collected from dairy cattle and native Korean cattle with diarrhea. Some of the Korean isolates have been identified from cases with significant diarrhea and no other detectable major enteric pathogens.

Japanese isolates have come from normal cattle and calves with diarrhea. Isolates from a calf with diarrhea and a nasal swab from healthy cattle have been reported in Canada. The serological evidence of a BEV epidemic has also been reported from Brazil and Italy. A strong association of BEV with some cattle diseases including diarrhea where no evidence of other pathologic agents is present indicates a causative role, but this is not definitive confirmation without evidence of experimental infection with the virus.

BEVs are very stable in environmental conditions due to resistance to changes in pH, temperature, salinity and disinfectants. The ease of transmission, high amounts of virus scattered in every gram of feces, the role of subclinical infected animals and the virus’s survival in water and soil for a long time, make this virus a common contaminant.

The research articles related to BEVs were written mostly in the 1960s. After a couple reports in the mid-1980s, the infection remained nearly unnoticed until recently. Acute infections with poor prognosis have been reported from different parts of the world such as fatal enteric disease in a heifer in the U.S., respiratory disorders in cattle in China, severe diarrheal disease in a yak in the Qinghai-Tibetan Plateau and severe respiratory infection in an Alpaca in U.S. Virus isolates from feces samples of healthy and diarrheic animals have been examined on a genomic level.

A new enterovirus strain was isolated from a cattle farm that had animals suffering from an unknown disease of high morbidity and mortality.

Prevention

Effective disinfecting and cleansing of facilities, in addition to quarantine and removal of infected individuals from herds are fundamental considerations, since no vaccine to prevent or control BEV infection is available.

Treatment

Since the causative agent is viral, no specific treatment for bovine enterovirus (BEV) infection is available other than symptomatic treatment and good nursing care. The importance of good animal husbandry including hygiene and nutrition cannot be over-emphasized for general control of most infections, especially viral infections

Appropriate isolation of infected animals and hygiene measures should be employed to minimize the spread of disease during an outbreak.