Little reason to suspect Ebola is now airborne

THE Ebola outbreak has continued unabated for nearly six months now, since March. It currently spans Liberia, Guinea, Sierra Leone and Nigeria in West Africa, as well as the Democratic Republic of the Congo in Central Africa.

This week, the World Health Organisation said that thousands of new cases will be seen this month in Liberia, the hardest-hit nation. It is urging wealthy nations to help fight the scourge.

But this appeal is encouraging conspiracy theorists, who claim, among other things, that Ebola is spreading so fast because it actually does not take contact with body fluids for one to catch it, as experts insist. They say the bug is, in fact, airborne.

This matters because an airborne infection such as the severe acute respiratory syndrome spreads much more easily than an infection like hepatitis C, which can be transmitted only by body fluids such as blood, sweat, saliva, vomitus, urine, stools or semen of an infected person.

From 1976, when Ebola was first recognised, to the present, it has infected about 5,000 people and killed over 3,000. If the virus were efficiently airborne, the number of cases would be seriously much higher than this.

Still, doubters say the virus may have mutated to become transmissible by air. Why else is it spreading like wildfire now?

First, genomic studies have not identified any such mutations: The genome of the Zaire strain of the virus causing the current epidemic remains unchanged.

Second, even in very sick patients, the load of the virus in the lungs is not heavy. Instead, it is found mainly in the blood. Thus, the symptoms are heavy sweating, vomiting and diarrhoea, not coughing or sneezing. There is not a lot of congestion in the lungs, so coughing is not a prominent symptom, which is needed for Ebola to spread by air.

Third, some doubters point to a Canadian study published in 2012 which reported an experiment suggesting that pigs may be able to infect monkeys with Ebola through the air. In the study, monkeys were kept in cages near a pen of pigs infected with Ebola.

The two groups never came into physical contact. Yet the monkeys got infected anyway. So wasn't this proof positive of Ebola's airborne transmission?

Actually, mucus from the pigs' snouts may have got onto the surface of the pig pen. So when the pen was washed, water with the mucus might have splashed into the monkey cages, infecting the primates. Thus, this experiment did not necessarily show airborne transmission of the virus.

Still, it is possible that the virus got into the monkey cages as an airborne spray from the snouts of the pigs. One reason to suspect this is that Ebola is uncharacteristically a respiratory illness in swine, but not in humans.

That is, the virus manifests itself differently in swine and in primates: Pigs can generate more droplets carrying the virus.

Vets note that pigs grunt, sniff, snuffle and snort to keep their nostrils clear when they eat. Even a healthy pig generates a lot of nasal mucus which it uses to trap the dirt that gets into its snout. Then it snorts to expel big blobs of the mucus, thus getting rid of the dirt. Pigs thus produce large droplets that primates cannot.

All this means that, even if pigs could spread Ebola through the air, people cannot. That is, primate-to-primate transmission is unlikely to be airborne because primate mouths and noses cannot generate the large droplets that pig snouts can.

What all this suggests is that, as long as we do not have infected pigs sharing our living space, the airborne route for Ebola, if there is one, is of no significance to us. So, keep clear of pig farms.

Historically, the Nipah virus jumped from bats to pigs in a farm and thence to humans. The natural host of Ebola is likewise the fruit bat, but pigs are not known to be an intermediate host for the virus, though they are used in laboratories to study it. Still, just avoid pigs and pig farms.

In a study published recently, a researcher housed two rhesus monkeys infected with Ebola in cages near two healthy ones, making sure that physical contact between the two groups was impossible. (No pigs were involved in this study.)

While the infected monkeys died six days later, the healthy ones remained Ebola-free, confirming that there was no airborne monkey-to-monkey transmission of the virus.

Finally, sceptics make much of the fact that many health-care workers have been infected. In Liberia, for example, 152 medical workers have been infected, of whom 79 have died, to date.

Sceptics note that these people knew about the illness and assiduously employed patient isolation practices and barrier nursing, using masks, boots, goggles, gloves and gowns to protect themselves.

The sceptics compare Ebola with hepatitis C, which spreads through body fluids but does not infect doctors and nurses so easily. If the typical precautions are failing, they say, does that not suggest Ebola could be spreading through the air instead?

In fact, not all health-care workers in Africa have access to such equipment. Especially when there is an outbreak in a far-flung and isolated rural backwater, the minimalist health-care facilities are not likely to have such gear.

Experts note that in locales where some of such equipment may be available, they may be less effective than we expect because it gets very hot inside the gowns.

There may be no air-conditioning, so the wearer sweats profusely. Sweat may get into the eyes as the nurse or doctor is trying to perform a procedure on the patient, such as dressing a wound or setting up a drip. These conditions may cause a health-care worker to make mistakes.

Or, a patient may uncontrollably vomit, defecate or urinate on a worker who has just shed his gear.

So the fact that many medical personnel "who should know better" are being infected need not mean that Ebola is now airborne.

In sum, there is little reason to suspect that airborne human-to- human transmission of Ebola may be occurring in the field at this time. It is quite clear that people are infected only through contact with the body fluids of infectious Ebola patients.

andyho@sph.com.sg