Many cases blamed on a single individual who appears to have caught virus for second time

Health officials are investigating an alarming spike in Ebola cases in the Democratic Republic of the Congo, with many blamed on a single individual who appears to have contracted the disease for a second time this year.

Amid the struggle to bring the 16-month outbreak under control, the World Health Organization noted an almost 300% increase in cases in the last three weeks, with 17 of 27 linked to a single chain of transmission.

According to officials, it appears to be the second time the person has been documented as suffering from Ebola in six months. An investigation is being held to understand the circumstances around the case.

Ten cases were notified on Wednesday in Mabalako, North Kivu province, where the individual is believed to be from, after another six on Tuesday, according to officials who noted that three out of the six were practitioners of traditional medicine.

Ebola responders face deadly attacks. We must step up security in DRC Read more

The spike – and the worrying circumstances behind it – appears to buck a trend towards a declining number of cases, although security issues in the key zones of Beni, Biakato and Mangina had recently paralysed the response after violent attacks on health workers.

Among the possibilities being examined are reinfection with the disease – which would ring the most serious alarm bells as no case of reinfection has ever been recorded before – or a relapse.

Q&A What is Ebola? Show Hide Ebola virus disease (EVD) first appeared in 1976 in two outbreaks, located in what is now known as South Sudan and the Democratic Republic of Congo. The latter outbreak was in a village near the Ebola River, giving the disease its name. Ebola causes fever, aches and diarrhoea and attacks the immune system, causing blood clotting cells to malfunction so that victims bleed extensively and die if their immune system cannot fight off the viral infection. It is spread from person to person through body fluids. Infected patients are isolated and treated by medical teams wearing full protective body suits who try to boost their immune response. The average case fatality rate is around 50% - and health-care workers have frequently been infected. Burial ceremonies involving direct contact with the body of the deceased can also contribute to transmission. A vaccine, still experimental, has proven to be highly effective in preventing the disease, according to the World Health Organization.

While rare cases of relapse have been documented, in which a person who has recovered from Ebola gets its symptoms again, reinfection would mean a person who has recovered has been infected anew with the virus by another person, a circumstance so far undocumented.

Experts have long been anxious about the risk of recurrence because the virus can persist for months in areas of the body that are immunologically protected, including semen, vaginal fluids, sweat, aqueous humour, urine, breast milk and even spinal fluid after initial onset and recovery.

That has led researchers to speculate about the continued risk of transmission in individuals not showing any symptoms, including through sexual activity, leading to reactivation of the illness.

Reinfection, relapse and recurrence are all sources of acute concern in controlling the outbreak, as Ebola survivors are employed widely in treatment centres in DRC on the assumption they cannot usually recontract or transmit the disease.

In July another patient died from what was also presumed to be a relapse or reinfection, calling into question the assumption that Ebola survivors have lifelong immunity from the virus.

According to figures from the African Union as of 8 December, the Ebola outbreak in DRC has claimed 2,209 lives since it broke out, with 3,327 recorded cases.