New research from the University of East Anglia shows that the risk of catching Ebola from a survivor is very low.
A study published today in PLOS Neglected Tropical Diseases shows that while the Ebola virus may persist for some considerable time in certain body locations, it is typically cleared from the blood within 16 days - meaning that the risk of infection from contact with a survivor is low.
A big exception to this however is transmission via sexual intercourse due to the virus' presence in semen for many months after a patient has otherwise recovered.
The research team set out to discover how long the Ebola virus persists in different human body fluids.
Lead researcher Prof Paul Hunter from UEA's Norwich Medical School said: "The recent Ebola outbreak was very different to anything we'd seen before - it lasted longer than any previous Ebola emergence, and it left behind thousands of survivors.
"We wanted to know how long the Ebola virus persists in different body fluids after people have recovered - in order to assess how much of a transmission risk those survivors pose to their family, communities and medical professionals."
The team sifted through nearly 6,000 articles on Ebola to pinpoint those which documented the presence of the virus in survivors' body fluids - including blood, urine, semen, sweat, breast milk, faeces, and vaginal fluids.
- The Ebola virus has been found in most types of body fluid - but not every sample from every symptomatic patient.
- Infected blood appears to be the most infectious body fluid, with 'viral loads' observed to be very high.
- Only 5 per cent of patients carried the virus in their blood after 16 days of illness. The longest amount of time for a survivor to carry the virus in their blood was 29 days.
- Most survivors transitioned from actively having the illness to convalescence at around day 16 or 17.
- 70 per cent of semen samples from male survivors tested positive for the virus in the first seven months after illness (in data available before mid 2015).
- Apart from blood and semen, most other body fluids pose a low infectious risk.
- There was too little evidence to allow a strong conclusion on breastmilk.
Prof Hunter said: "This research is important because there has been little evidence to give definitive guidance about which body fluids are infectious and when they pose a risk. Above all, this research strengthens the case for scientific evidence to be used rather than fear when managing infectious diseases such as Ebola.
"This study shows that the Ebola virus is usually no longer present in most body fluids after a few weeks (apart from in semen), but other later health complications have been widely reported, especially in the most recent outbreak. We did not find any evidence that the virus can reactivate to the point that it becomes infectious for others by non-sexual contact.
"Consequently transmission from social contact with an Ebola survivor is not something that is likely to be a problem, even if that person is suffering from longer term complications.
"Nevertheless, this recent outbreak was so large that this is the first time there has been such a huge number of Ebola survivors to study, and it's possible that we will find out that after-effects are more common than previously thought."
The research was funded by National Institute for Health Research (NIHR) Health Protection Research Unit on Emergency Preparedness and Response.
'Presence and Persistence of Ebola or Marburg Virus in Patients and Survivors: A Rapid Systematic Review' is published in the journal PLOS Neglected Tropical Diseases on Monday, February 29 at 19:00 GMT.