Brief review of coronaviruses in humans and animals

In 2020, humanity has faced a health, economic and social catastrophe because of the novel coronavirus, but what are these infectious-contagious viral agents and how did they arise?

The surprising Coronaviridae family 

Coronaviruses are a family of RNA viruses with a lipid bilayer envelope composed of more than 15 pathogens that affect humans, mammals and birds. They are pleomorphic particles that measure around 100 nm in diameter (range between 60 and 220), with spike-shaped projections ("S" glycoproteins) on their surface.

Coronaviruses carry a 27 to 31 kilobase positive-sense single-stranded RNA, a capsid of a phosphorylated protein linked to the genome forming a ribonucleoprotein helix. They replicate in the cytoplasm of vertebrate cells and are transmitted horizontally by the respiratory route through aerosols (coughing, sneezing), saliva, mucus and feces. They produce respiratory and gastrointestinal diseases.

Human coronaviruses

In recent years, three major infectious diseases caused by coronaviruses have emerged in humans:

1. SARS-CoV-1 (Severe Acute Respiratory Syndrome Coronavirus 1)

SARS-CoV-1 (Severe Acute Respiratory Syndrome Coronavirus) was first reported in November 2002 in Guangzhou, China. It spread to numerous countries in Asia, Europe and America. It infected 8,422 people and caused 916 deaths. Since 2004, there have been no cases in the world. It is considered as a zoonosis, being the bat the reservoir animal from which it emerged. It belongs to the Betacoronavirus genus.

2. MERS-CoV (Middle East Respiratory Syndrome)

MERS-CoV (Middle East Respiratory Syndrome) was reported in Saudi Arabia in 2012. Camels and dromedaries are an important natural reservoir of the virus and from them, it passed to humans. It affected other countries such as the United Arab Emirates, Egypt, Oman and Qatar. It is a zoonotic disease. The causative agent is a Betacoronavirus.

3. SARS-CoV-2 (Severe Acute Respiratory Syndrome 2)

SARS-CoV-2 (Acute Severe Respiratory Syndrome 2) is responsible for the global pandemic that is currently affecting all continents. COVID-19 (Coronavirus Disease-19) was reported for the first time on December 31, 2019, in the city of Wuhan, capital of the Chinese province of Hubei. It is an enveloped RNA virus that enters the host cell by binding to the angiotensin-converting enzyme 2 receptor. It is part of the Betacoronavirus genus.

By mid-May 2020, this microorganism showed a very high contagious capacity and a fatality rate of approximately 1 to 4%. It has caused millions of infections and hundreds of thousands of deaths in China, Italy, Spain, France, Great Britain, Europe, the United States, Latin America and the rest of the world.

In addition, the novel coronavirus has forced countries to take strict social distancing and lockdown measures, which have affected economies worldwide. This has caused a global catastrophe without historical precedent, at all social, economic and political levels. 

The last great pandemic in humanity was caused by the influenza virus subtype A/H1N1, poorly known as “Spanish flu.” It emerged in the United States and passed to Europe during the First World War in 1918, causing the death of millions of people.

The return to the new normal will be different. Our lives will have changed forever on a global level. It will be a “before and after” of the SARS-CoV-2 pandemic.

Coronavirus in domestic animals

In addition to the coronaviruses that have caused illness in humans, there are others that affect animals. Here is a brief review:

• Coronavirus in birds: Avian infectious bronchitis

The avian infectious bronchitis (IB) is a highly contagious, acute viral respiratory disease that affects broilers and hens and is characterized by tracheal rales, coughing, and sneezing. In adult birds, it causes a severe drop in egg production. Certain strains cause a nephritis-nephrosis syndrome.

The IB has a morbidity rate close to 100% and a fatality rate of 1 to 5%. It can also affect turkeys and pheasants. It has a worldwide distribution, but it was reported for the first time in North Dakota, United States, in 1930. The causative agent is a gammacoronavirus, which was isolated in 1936. It causes serious economic losses in the world poultry industry.

• Swine coronaviruses

There are five infectious pathologies caused by coronaviruses in pigs:

1. Transmissible gastroenteritis virus (TGE). 1946. Genus Alpha.
2. Porcine hemagglutinating encephalomyelitis virus (PHEV). 1962. Genus Alpha.
3. Porcine epidemic diarrhea virus (PEDV). 1977. Genus Beta.
4. Porcine respiratory coronavirus (PRCoV). 1984. Genus Beta.
5. Porcine deltacoronavirus (PDCoV). 2009. Genus Delta.

• Coronaviruses in cattle

1. Neonatal calf diarrheal (NCD). Genus Beta.
2. Bovine coronavirus (BCV), which causes winter dysentery. Genus Beta.
3. Bovine respiratory disease (BRD). Genus Beta.

• Canine coronavirus

1. Canine coronavirus (CCoV), which causes a highly contagious intestinal disease in dogs. Genus Alpha.

• Feline coronaviruses

1. Feline enteric coronavirus (FECV). Genus Alpha.
2. Feline infectious peritonitis virus (FIPV). Genus Alpha.

Anthropozoonosis

An anthropozoonosis is defined as an infectious-contagious disease that can be transmitted from a human to an animal. Given the pandemic, would it be possible that humans transmit, for example, COVID-19 to farm animals, such as broilers, hens, pigs, dairy cattle, beef cattle, etc.? In other words, is an infected asymptomatic livestock farm worker capable of transmitting a coronavirus to animals? The answer is yes!

Researchers have found the infectious agent SARS-CoV-2 in domestic cats and in tigers in zoos. In addition, a worker in a pig farm infected by the SARS-CoV-2 virus, as an asymptomatic carrier, could transmit the disease to pigs (Sus scrofa domestica), an animal species that is highly susceptible to coronaviruses.

VIRUS	DISEASE	SPECIES	GENDER
TGE-CoV	Transmissible gastroenteritis (GTE)	Pig	α
PHE-CoV	Porcine hemagglutinating encephalomyelitis coronavirus infection	Pig
PED-CoV	Porcine epidemic diarrhea virus (PEDV)	Pig
PRC-CoV	Porcine respiratory coronavirus	Pig
FIE-CoV	Feline enteric coronavirus (FECV)	Cat
FIP-CoV	Feline infectious peritonitis virus (FIPV)	Cat
AIID-CoV	Enteric canine coronavirus infection	Dog
CNDS-CoV	Neonatal calf diarrhea	Bovine	β
ABD-CoV	Winter dysentery (diarrhoea in adult cattle)	Bovine
BRS-CoV	Bovine respiratory disease (BRD)	Bovine
SARS-CoV-1	Severe acute respiratory syndrome (zoonosis)	Human
MERS-CoV	Middle east respiratory syndrome (zoonosis)	Human
SARS-CoV-2	Severe acute respiratory syndrome/covid-19 (zoonosis)	Human
AIB-CoV	Avian infectious bronchitis (IB)	Hen	γ
TCE-CoV	Coronaviral enteritis of turkeys	Turkey	γ
PCE-CoV	Porcine coronavirus enteritis	Pig	δ

View our continuing coverage of the coronavirus/COVID-19 pandemic.