INTRODUCTION:

Hemagglutinin-esterase is a protein that we can find in the envelope of some viruses. Its function is related with the pathogenicity of the virus and with its interaction with the host. It may help the virus bind and enter the mucus layer of the intestinal way.

We can find this protein, in two virus families. They are coronaviridae, which include the genus coronavirus and torovirus and one virus of orthomixovidirae family. Next, we explain few characteristics about these viruses:

FAMILY CORONAVIRIDAE: Is a non-segmented, positive single-strand RNA family of viruses and the longest of any RNA virus. They have an envelope and helical nucleocapsid.

Genus Coronavirus: They cause respiratory, enteric and neurological infections in a large variety of mammals (humans, cows, horses…) and birds. They are transmitted by aerosols of respiratory secretion.

Their envelope carries two proteins, a receptor binding and a transmembrane glycoprotein, and in some cases a third glycoprotein, haemagglutinin-esterase.

Bovine coronavirus: This virus infects cattle and causes diarrhea in newborn calves. It is also known to be associated with winter dysentery in adult cattle and may be associated with respiratory illnesses, especially in feedlot cattle.

Murine hepatitis virus: This virus is of importance in that infection of rodents with MHV provides one of the best model systems for the study of human demyelinating diseases such as Multiple Sclerosis. MHV also causes hepatitis.

Rat sialodacryoadenitis coronavirus: Rats are the natural hosts for these extremely contagious coronaviruses. It is related to the mouse hepatitis virus (MVH), but isn’t the same. This virus infects rats only, and it induces a respiratory disease that affects the lacrimal, salivary and Harderian glands.

Puffinosis virus: It infects several species of seabirds and causes vesicular dermatitis.

Human coronavirus: It usually produces an afebrile cold in adults, characterized by nasal discharge, and malaise, and may exacerbate respiratory symptoms in asthmatic and chronic pulmonary disease patients. It’s implicated in gastroenteritis with a greater occurrence in children. It may also be associated with pneumonia and pleural reactions but rarely is manifested in neurological complications. Immunity is serotype specific; antigenic heterogeneity allows for multiple symptomatic reinfections.

Genus Torovirus: It is a non-segmented, positive single-strand RNA family of viruses. We can distinguish it from coronavirus, because its nucleocapsid is smaller, and has tubular helical structure. They cause enteric infections and can they are transmitted by the fecal-oral route.

Breda virus: This virus infects cattle and causes diarrhea in calves

Berne virus: The illnesses that it causes are the same as those in the Breda virus, but this one affects horses.

Human torovirus: It might possibly infect the gastrointestinal system, but this association is unclear. It might cause some respiratory diseases

FAMILY ORTHOMYXOVIRIDAE: Virions contain 7 or 8 segments of linear negative-sense single stranded RNA. Virions are enveloped and have pleomorphic or filamentous form. They are mainly pathogens of the upper respiratory tract of humans, horses, pigs and birds. Contact, aerosols or water transmits them.

Influenza C: Its infection usually results in either a very mild respiratory illness or may be asymptomatic.

In this family, only Influenza C expresses this protein, but Influenza A and Influenza B contains a similar one, haemagglutinin.