What Are Betacoronaviruses And How Do They Infect Humans?

Betacoronaviruses are a family of viruses that can infect humans and animals. They are best known for causing respiratory illnesses, ranging from the common cold to severe conditions like SARS, MERS, and COVID-19. They infect humans by attaching to specific proteins on the surface of our cells, then fusing with the cell membrane to release their genetic material inside.

What Are Betacoronaviruses And How Do They Infect Humans

Betacoronaviruses belong to the Coronaviridae family, a large group of viruses named for the crown-like spikes on their surface. This family is divided into four genera: alpha, beta, gamma, and delta. The beta genus is the one that has caused the most significant human disease.

Within the betacoronavirus group, there are several lineages. Some, like OC43 and HKU1, circulate widely and cause mild upper respiratory infections similar to the common cold. Others, like SARS-CoV, MERS-CoV, and SARS-CoV-2, have crossed from animals into humans and caused severe outbreaks.

The infection process begins when the virus comes into contact with a human cell. The spike protein on the virus’s surface acts like a key. It binds to a specific receptor on the host cell. For SARS-CoV-2, that receptor is called ACE2, which is found on cells in the lungs, heart, and blood vessels. For MERS-CoV, the receptor is different, called DPP4.

Once the spike protein locks onto the receptor, the virus membrane fuses with the host cell membrane. This action releases the virus’s RNA into the cell. The cell then reads that RNA and starts producing new viral parts, which assemble into new viruses. These new viruses exit the cell and go on to infect neighboring cells.

Which Betacoronaviruses Affect Humans?

Seven coronaviruses are known to infect humans. Four of them are betacoronaviruses that have been circulating in human populations for a long time. Two more are betacoronaviruses that cause severe disease but are not widely spread. One is the virus behind the COVID-19 pandemic.

The common cold betacoronaviruses are OC43 and HKU1. Most people are infected with these during childhood. They cause mild symptoms like a runny nose, sore throat, and cough. They are responsible for roughly 10 to 15 percent of common colds in adults.

The severe betacoronaviruses are SARS-CoV and MERS-CoV. SARS emerged in 2002 in China and caused a global outbreak before being contained. MERS emerged in 2012 in the Arabian Peninsula and continues to cause sporadic cases, often linked to contact with camels. Both viruses cause severe pneumonia and have higher death rates than COVID-19, though they spread less easily between humans.

SARS-CoV-2 is the most recent betacoronavirus to jump into humans. It emerged in late 2019 and caused the COVID-19 pandemic. It spreads more easily than SARS or MERS, which is why it infected so many people worldwide.

How Do Betacoronaviruses Spread Between People?

Betacoronaviruses spread primarily through respiratory droplets. When an infected person coughs, sneezes, talks, or breathes heavily, they release tiny droplets containing the virus. Another person can inhale these droplets, and the virus can then enter their respiratory tract.

Transmission can also occur through aerosols. These are smaller particles that can hang in the air for longer periods, especially in poorly ventilated indoor spaces. This mode of transmission is more significant for SARS-CoV-2 than for the common cold coronaviruses.

Surface transmission is possible but less common. If a person touches a contaminated surface and then touches their eyes, nose, or mouth, they could become infected. Studies have shown that coronaviruses can survive on surfaces for hours to days, depending on the material. However, the primary route of spread is through the air, not through touching objects.

Some betacoronaviruses have animal reservoirs. MERS-CoV is found in dromedary camels. SARS-CoV originated in bats, with an intermediate animal host likely involved. SARS-CoV-2 also likely originated in bats, though the exact intermediate host is still under investigation.

What Happens Inside the Body After Infection?

After the virus enters the respiratory tract, it begins infecting epithelial cells lining the airways. The immune system recognizes the infection and mounts a response. This response includes inflammation, which causes many of the symptoms people experience.

For the common cold betacoronaviruses, the infection stays mostly in the upper respiratory tract. Symptoms appear two to four days after exposure and last about a week. The illness is typically mild and resolves on its own.

For severe betacoronaviruses like SARS-CoV-2, the virus can travel deeper into the lungs. It infects cells in the alveoli, the tiny air sacs where oxygen exchange happens. This can trigger a strong inflammatory response called a cytokine storm, where the immune system overreacts and damages healthy lung tissue.

This damage can lead to acute respiratory distress syndrome (ARDS), a condition where fluid builds up in the lungs and oxygen levels in the blood drop dangerously low. This is the main cause of death from severe betacoronavirus infections.

Beyond the lungs, betacoronaviruses can affect other organs. The ACE2 receptor used by SARS-CoV-2 is present in many tissues, including the heart, kidneys, and digestive tract. This explains why some people experience heart problems, kidney injury, or digestive symptoms during or after infection.

How Do Symptoms Differ Between Betacoronavirus Types?

The symptoms depend on which betacoronavirus is causing the infection. The common cold types produce mild, self-limiting illness. The severe types can cause life-threatening pneumonia.

Common cold betacoronavirus symptoms include:

• Runny or stuffy nose
• Sore throat
• Cough
• Mild headache
• Low-grade fever

Severe betacoronavirus symptoms include:

• High fever
• Persistent dry cough
• Shortness of breath
• Chest pain
• Confusion or drowsiness in severe cases
• Low blood oxygen levels

Some people infected with SARS-CoV-2 have no symptoms at all. Others experience mild symptoms similar to a cold. A smaller percentage develop severe disease requiring hospitalization. Age and underlying health conditions are the strongest risk factors for severe disease.

Loss of taste and smell was a distinctive symptom of early COVID-19 infections. It is less prominent with newer variants but still occurs. This symptom is not typical of the common cold betacoronaviruses.

What Treatments Exist for Betacoronavirus Infections?

For common cold betacoronaviruses, treatment is supportive. Rest, fluids, and over-the-counter medications for fever and congestion are the standard approach. Antibiotics do not work against viruses and are not prescribed unless a bacterial infection develops as a complication.

For severe betacoronavirus infections, treatment depends on the specific virus and the severity of the illness. For COVID-19, several antiviral medications have been developed. These include remdesivir, which is given intravenously in hospitals, and oral medications like nirmatrelvir-ritonavir (Paxlovid), which can be taken at home if started early in the illness.

Corticosteroids like dexamethasone are used in hospitalized patients who need oxygen. These drugs reduce inflammation and have been shown to lower death rates in severe COVID-19 cases. They are not recommended for mild illness.

For MERS and SARS, no specific antiviral treatments have been proven effective in large clinical trials. Treatment focuses on supportive care, including oxygen therapy and management of complications. Some experimental treatments have been used, but evidence is limited.

Vaccines are the most effective tool against severe betacoronavirus disease. Vaccines for COVID-19 were developed rapidly and have been shown to dramatically reduce the risk of severe illness, hospitalization, and death. No vaccines currently exist for the common cold betacoronaviruses, and vaccine development for MERS is ongoing.

Can You Get Infected More Than Once?

Yes. Infection with one betacoronavirus does not provide lasting immunity against other types. Even within the same type, reinfection is possible.

For the common cold betacoronaviruses, immunity wanes quickly. People can be reinfected with OC43 or HKU1 multiple times throughout their lives. This is why colds are so common.

For SARS-CoV-2, immunity from infection or vaccination provides strong protection against severe disease for several months. However, protection against mild infection decreases over time, and new variants can evade some of the immune response. This is why booster shots are recommended for high-risk groups.

How Can You Reduce Your Risk of Infection?

The same basic measures reduce risk for all respiratory viruses, including betacoronaviruses. These measures are well established and supported by strong evidence.

Hand hygiene is important. Washing hands with soap and water for at least 20 seconds removes viruses from the skin. Alcohol-based hand sanitizers with at least 60 percent alcohol are also effective when soap is not available.

Avoiding close contact with sick people reduces exposure. If you are sick, staying home prevents spreading the virus to others. Wearing a high-quality mask in crowded indoor settings can reduce the risk of inhaling viral particles, especially during periods of high community transmission.

Improving indoor ventilation lowers the concentration of viral particles in the air. Opening windows, using air purifiers with HEPA filters, and ensuring HVAC systems are maintained all help.

Vaccination remains the most effective way to prevent severe disease from SARS-CoV-2. Staying up to date with recommended doses, including boosters for eligible individuals, significantly reduces the risk of hospitalization and death.