Camels are the source of Middle East respiratory syndrome coronavirus (MERS-CoV), but it's still not clear how the virus is jumping to humans, the World Health Organization (WHO) said yesterday in a summary of its latest thinking on the disease, based on cases and scientific reports.
The agency also raised concerns about transmission of the disease in hospitals, which seems to be fueling a good portion of the limited human-to-human spread of the virus.
The WHO's fresh assessment came with a separate statement revealing more about six recent cases reported by Saudi Arabia and on the eve of yet another new case reported by the country's health ministry.
The new WHO review is its first on MERS since Jan 20. Since then, researchers have published three major animal studies, and health officials from five different Middle Eastern countries have reported 28 human infections, 10 fatal, to the WHO.
Clues from animal studies
Genetic sequencing conducted in two of the studies—one on camels in Egypt and one on an infected camel linked to a human case in Saudi Arabia—found high similarity to MERS-CoV viruses that have infected people.
In the third study, testing found evidence of the virus in a large number of camels across Saudi Arabia, but not in goats and sheep. The same study looked at archived specimens hinted that camels have been exposed to the virus as far back as 1992.
Genetic sequencing doesn't just show the similarity between the camel and human viruses, it also seems suggest that human disease patterns result from repeated introductions into human populations from camels, with only limited ongoing transmission in humans, the WHO said.
However, less clear is how the virus is transmitting from camels to humans. The WHO said that so far, its analysis of primary cases—those not infected by other humans—suggests that transmission is indirect, because most patients lack a recent history of direct contact with camels.
"As such, discovery of the route of transmission between camels and humans remains critical to stopping the initial introduction into human populations," the WHO said.
Until more is known about how the virus is spilling over, people at high risk of severe disease, especially those with underlying conditions, should take precautions when visiting farms and markets where camels are present, according to the WHO.
The agency said exposure to camels might vary among different countries, and it's possible that nations with large camel populations are missing some human infections. It urged those countries to be vigilant with their surveillance and test people who have severe respiratory disease, including pneumonia, regardless of travel history.
Healthcare transmission worries
Transmission of the disease in healthcare settings and in households is an ongoing concern, and though the events seem to be self-limited, they will likely continue until health officials are able to identify and interrupt the transmission route between animals and humans, the WHO said in the summary report.
Four of the 28 cases reported since Jan 20 appear to have been infected in healthcare settings, and three of them seem to have been infected by undetected cases, the WHO noted.
The illnesses linked to unrecognized MERS-CoV in the facilities is a reminder of how important it is to rigorously follow infections in patients with respiratory infections, even when MERS-CoV is not yet detected, the WHO said.
Details about recent Saudi cases
In looking at the patient characteristics so far, primary cases seem to be older and skewed toward men, the WHO said. A separate statement providing more details about six recent reports, one fatal, that it received from Saudi Arabia seemed to underscore that point: All are men, ages 45 to 86. All are from the Riyadh region.
Illness onsets range from Feb 23 through March 11. All five of the survivors are hospitalized in critical condition, and all have underlying medical conditions. Three of the patients have a history of exposure to camels.
The patient who died is an 86-year-old man who got sick on Mar 11 and died on Mar 19. The WHO said he had no history of exposure to animals.
So far the WHO has been notified of 206 lab-confirmed MERS-CoV cases, including 86 deaths.
Saudi Arabia announces new case
Meanwhile, Saudi Arabia's health ministry today announced another new MERS case but included few details. The patient is a 26-year-old man from Jeddah, according to a machine translation of an Arabic statement from the ministry's Web site.
Mar 27 WHO MERS-CoV summary and literature update
Mar 27 WHO statement on Saudi cases
Mar 28 Saudi Arabia health ministry statement