Introduction

Bovine enterovirus (BEV) is a picornavirus

Picornavirus

A picornavirus is a virus belonging to the family Picornaviridae. Picornaviruses are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual because it has a protein on the 5' end that is used as a primer for transcription by RNA polymerase...

 of the genus enterovirus

Enterovirus

Enteroviruses are a genus of ssRNA viruses associated with several human and mammalian diseases. Serologic studies have distinguished 66 human enterovirus serotypes on the basis of antibody neutralization tests. Additional antigenic variants have been defined within several of the serotypes on the...

. The virus may also be referred to as enteric cytopathic bovine orphan virus (ECBO). It is endemic in cattle populations and although normally fairly non-pathogenic it can cause reproductive, respiratory or enteric disease - particularly when the animal is concurrently infected with another pathogen. BEV has a non-enveloped, icosahedral protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 capsid composed of four structural proteins, VP1, VP2, VP3 and VP4. The capsid has a diameter of 27 nm and encloses a single stranded positive sense RNA

RNA

Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....

 genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 of approximately 7500 bases.

The bovine enteroviruses are endemic in cattle populations worldwide. BEVs were originally classified into seven serotypes but are now accepted as falling into two serotypes, 1 and 2, which are further classified into subtypes. BEV strain VG-5-27 of serotype 1, subtype 1 is the most extensively studied. The tissue tropism of serotype 1 is extremely broad, including human, sheep, horse, dog, camel and other mammalian hosts. BEV-like sequences have even been reported in shellfish from water contaminated with bovine faeces. Serotype 2 viruses are only found in domestic cattle.

The virus is spread horizontally by the oro-fecal or respiratory route. It may be shed for several months after infection. It is not a zoonosis.

Structure

In common with other picornaviruses, the capsid of BEV is composed of 60 copies of each of four structural proteins, VP1, VP2, VP3 and VP4, in icosahedral symmetry. The capsid is non-enveloped and roughly spherical with an outer radius of 159 Ångström

Ångström

The angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....

 and an inner radius of 107 Ångström. The outer surface of BEV is smoother than the closely related poliovirus

Poliovirus

Poliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is...

 due to the truncation of surface protein loops in BEV. It is also smoother than the related human rhinovirus

Rhinovirus

Human rhinoviruses are the most common viral infective agents in humans and are the predominant cause of the common cold. Rhinovirus infection proliferates in temperatures between 33–35 °C , and this may be why it occurs primarily in the nose...

 due to the extension of a surface loop in BEV. The three antigenic sites of BEV all occur on a surface ridge at the junction between VP1, VP2 and VP3. BEV has a crater-like depression at the icosahedral 5-fold axis which descends into a cylindrical hole of 10 Ångström in diameter which runs almost to the inner surface of the capsid. A hydrophobic pocket contained within VP1 contains a myristic acid

Myristic acid

Myristic acid, also called tetradecanoic acid, is a common saturated fatty acid with the molecular formula CH312COOH. A myristate is a salt or ester of myristic acid....

 molecule, the removal of which appears to be a pre-requisite for virus uncoating.

Replication

In order to replicate, BEV must attach to the host cell surface receptor, penetrate into the cell cytoplasm and the genome must be uncoated. The host cell surface receptor for BEV has yet to be identified but is sensitive to neuraminidase (1).

Clinical Signs of Infection

Most cattle show no clinical signs when infected with the virus. However abortion

Abortion

Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...

, stillbirth

Stillbirth

A stillbirth occurs when a fetus has died in the uterus. The Australian definition specifies that fetal death is termed a stillbirth after 20 weeks gestation or the fetus weighs more than . Once the fetus has died the mother still has contractions and remains undelivered. The term is often used in...

, infertility

Infertility

Infertility primarily refers to the biological inability of a person to contribute to conception. Infertility may also refer to the state of a woman who is unable to carry a pregnancy to full term...

 and neonatal mortality can occur following infection of the reproductive tract. Enteric signs include diarrhea

Diarrhea

Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

 and weight loss, and respiratory infection can produce a mucoid nasal discharge.

Diagnosis

As clinical signs are fairly non-specific and bovine enterovirus is ubiquitous in cattle populations it necessary to rule out other causes of disease before diagnosing enterovirus as the cause of disease. Electron microscopy, PCR, complement fixation, antibody fluorescence

Immunofluorescence

Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...

 and haemagglutination can be used to identify the virus in tissues or secretions.

Treatment & Control

Treatment is symptomatic

Symptomatic treatment

Symptomatic treatment is any medical therapy of a disease that only affects its symptoms, not its cause, i.e., its etiology. It is usually aimed at reducing the signs and symptoms for the comfort and well-being of the patient, but it also may be useful in reducing organic consequences and sequelae...

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