MERS, SARS and Emerging Respiratory Viruses
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Direct answer
MERS, SARS and avian influenza H5N1 are emerging zoonotic respiratory viruses that cause severe pneumonia after crossing from animals to humans. SARS-CoV and MERS-CoV are coronaviruses, whereas H5N1 is an influenza A virus that spreads from infected poultry. Control rests on case definitions, isolation, strict infection control and surveillance, because the coronaviruses have no licensed specific antiviral.
What you must remember
- SARS-CoV: emerged in 2002 and spread widely in hospitals; bats are the reservoir and civets were an intermediate host.
- MERS-CoV: identified in 2012 in the Arabian Peninsula, with dromedary camels as the main animal source.
- Receptors: SARS-CoV uses ACE2, whereas MERS-CoV uses dipeptidyl peptidase 4 (DPP4, also called CD26).
- Case fatality: roughly one in ten for SARS and about one-third for MERS among reported cases.
- Incubation: up to 14 days for MERS, which defines the contact follow-up period.
- Avian influenza H5N1: highly pathogenic, acquired from infected poultry, with high mortality and limited human-to-human spread.
- Infection control: single negative-pressure rooms, N95 respirators for aerosol-generating procedures, and contact and droplet precautions.
- Surveillance: cases are notified through the Integrated Disease Surveillance Programme in India, using suspect, probable and confirmed case definitions.
Comparing the three threats
A healthcare worker in a Gulf hospital develops fever and breathlessness after caring for a patient with severe pneumonia, and the team must decide whether to suspect MERS. The table compares the three viruses by source, route and key lesson, which helps in choosing the right precautions.
| Feature | SARS-CoV | MERS-CoV | Avian influenza H5N1 |
|---|---|---|---|
| Reservoir or source | Bats; civets as intermediate host | Dromedary camels | Infected birds and poultry |
| Main transmission | Droplets and close contact; hospital spread | Close contact, especially in hospitals | Direct contact with birds; limited human spread |
| Approximate fatality | About one in ten | About one-third | High among reported cases |
| Key lesson | Super-spreading in hospitals | Nosocomial clusters | Surveillance of poultry and farm workers |
Because all three can cause severe pneumonia, the same principles apply: identify the exposure history early, isolate the patient and protect staff. Exposure to camels, live poultry markets or a hospital with confirmed cases should raise suspicion. Hand hygiene remains the cornerstone of prevention in every setting.
Where the exam tries to catch you
Questions on this topic usually test the reservoir, the receptor and the precautions for aerosol-generating procedures.
- Trap: MERS spreads efficiently through casual community contact. Correct: it spreads mainly through close contact, especially in hospitals, with limited sustained community transmission.
- Trap: SARS is currently circulating in humans. Correct: it has not recurred with sustained human transmission since the early 2000s, though laboratory surveillance continues.
- Trap: avian influenza spreads between humans like seasonal influenza. Correct: H5N1 human infection is mainly acquired from birds, and person-to-person spread has been sporadic and limited.
- Trap: a surgical mask is enough for aerosol-generating procedures. Correct: a fit-tested N95 or higher respirator and a negative-pressure room are needed.
Frequently asked questions
What is the reservoir of MERS coronavirus?
Dromedary camels are the main animal reservoir of MERS coronavirus, and bats are thought to be the original source. Human infection usually follows close contact with camels or their products. Hospital clusters have amplified spread, so infection control is central to prevention.
Which receptor does MERS coronavirus use for entry?
MERS coronavirus uses dipeptidyl peptidase 4 (DPP4), also called CD26, as its receptor. SARS coronavirus instead uses ACE2 as its receptor. This difference in receptor usage is a classic examination point when comparing the two viruses.
What infection control measures are needed for suspected MERS or SARS?
Suspected MERS or SARS patients need isolation with contact and droplet precautions. Airborne precautions and a fit-tested N95 respirator are required for aerosol-generating procedures. Single rooms with negative pressure are preferred for these patients.
Why does avian influenza H5N1 cause high mortality in humans?
Avian influenza H5N1 causes high mortality in humans through severe viral pneumonia and multi-organ involvement, though the exact mechanism is still studied. Human cases are usually linked to close contact with infected poultry. Oseltamivir is used if it is started early, and sporadic human-to-human transmission has been limited.
What is the incubation period of MERS?
The incubation period of MERS is usually up to 14 days, which is why contacts are followed up for that duration. Clinical features include fever, cough and shortness of breath, and severe pneumonia may follow. The same window is used when defining contacts for quarantine.