The Ebola virus is transmitted among humans through close and direct physical contact with infected bodily fluids, the most infectious being blood, faeces and vomit.
The Ebola virus has also been detected in breast milk, urine and semen. In a convalescent male, the virus can persist in semen for at least 70 days; one study suggests persistence for more than 90 days.
Saliva and tears may also carry some risk. However, the studies implicating these additional bodily fluids were extremely limited in sample size and the science is inconclusive. In studies of saliva, the virus was found most frequently in patients at a severe stage of illness. The whole live virus has never been isolated from sweat.
The Ebola virus can also be transmitted indirectly, by contact with previously contaminated surfaces and objects. The risk of transmission from these surfaces is low and can be reduced even further by appropriate cleaning and disinfection procedures.
Not an airborne virus
Ebola virus disease is not an airborne infection. Airborne spread among humans implies inhalation of an infectious dose of virus from a suspended cloud of small dried droplets.
This mode of transmission has not been observed during extensive studies of the Ebola virus over several decades.
Common sense and observation tell us that spread of the virus via coughing or sneezing is rare, if it happens at all. Epidemiological data emerging from the outbreak are not consistent with the pattern of spread seen with airborne viruses, like those that cause measles and chickenpox, or the airborne bacterium that causes tuberculosis.
Theoretically, wet and bigger droplets from a heavily infected individual, who has respiratory symptoms caused by other conditions or who vomits violently, could transmit the virus over a short distance to another nearby person.
This could happen when virus-laden heavy droplets are directly propelled, by coughing or sneezing (which does not mean airborne transmission) onto the mucus membranes or skin with cuts or abrasions of another person.
WHO is not aware of any studies that actually document this mode of transmission. On the contrary, good quality studies from previous Ebola outbreaks show that all cases were infected by direct close contact with symptomatic patients.
No evidence for mutation of this virus
Moreover, scientists are unaware of any virus that has dramatically changed its mode of transmission. For example, the H5N1 avian influenza virus, which has caused sporadic human cases since 1997, is now endemic in chickens and ducks in large parts of Asia.
That virus has probably circulated through many billions of birds for at least two decades. Its mode of transmission remains basically unchanged.
Speculation that Ebola virus disease might mutate into a form that could easily spread among humans through the air is just that: speculation, unsubstantiated by any evidence.
This kind of speculation is unfounded but understandable as health officials race to catch up with this fast-moving and rapidly evolving outbreak.
To stop this outbreak, more needs to be done to implement on a much larger scale well-known protective and preventive measures. Abundant evidence has documented their effectiveness.
Meanwhile WHO has declared end of Ebola outbreak in Nigeria:
Statement
20 October 2014
The Ebola virus was introduced into Nigeria on 20 July when an infected Liberian man arrived by aeroplane into Lagos, Africa’s most populous city. The man, who died in hospital 5 days later, set off a chain of transmission that infected a total of 19 people, of whom 7 died.
According to WHO recommendations, the end of an Ebola virus disease outbreak in a country can be declared once 42 days have passed and no new cases have been detected. The 42 days represents twice the maximum incubation period for Ebola (21 days). This 42-day period starts from the last day that any person in the country had contact with a confirmed or probable Ebola case.
Today, 20 October, Nigeria reached that 42-day mark and is now considered free of Ebola transmission.
WHO commends the Nigerian Government’s strong leadership and effective coordination of the response that included the rapid establishment of an Emergency Operations Centre.
When the first Ebola case was confirmed in July, health officials immediately repurposed technologies and infrastructures from WHO and other partners to help find cases and track potential chains of transmission of Ebola virus disease.
WHO, United States Centers for Disease Control and Prevention (CDC), Médecins Sans Frontičres (MSF), UNICEF and other partners supported the Nigerian Government with expertise for outbreak investigation, risk assessment, contact tracing and clinical care.
Strong public awareness campaigns, teamed with early engagement of traditional, religious and community leaders, also played a key role in successful containment of this outbreak.
The Nigerian government and staff in the WHO country office are well aware that the country remains vulnerable to another imported case. The surveillance system remains at a level of high alert.
Nigeria has revised its national preparedness and response plan to ensure that the country is well prepared for other imported cases of the disease.
Source: WHO.
Photo: WHO Director-General Margaret Chan.
Here is Margaret Chan speaking on the Ebola outbreak in August this year:
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