An Ebola outbreak in Nigeria’s oil producing hub of Port Harcourt could spread wider and faster than in the financial capital, Lagos, the World Health Organization warned on Thursday.

The UN health body said the virus’ arrival in Port Harcourt, 435 kilometres (270 miles) east of Lagos and home to oil and gas majors such as Shell, Total and Chevron, showed “multiple high-risk opportunities for transmission of the virus to others”.

Of the 255 people currently under surveillance for signs of the disease, the WHO said 60 were considered to have had “high-risk or very high-risk exposure”.

Until the Port Harcourt case was announced, Nigeria’s government had indicated that the virus was contained in Lagos.

But the warning will raise fears about the spread of the virus in Africa’s most populous nation, top economy and biggest oil producer plus its health sector’s ability to cope with a wider outbreak.

Ebola, which has hit five countries in West Africa and caused nearly 2,000 deaths this year, first arrived in Nigeria when a Liberian finance ministry official died in Lagos on July 25.

He was taken from the city’s airport to a private hospital by two officials from the West African regional bloc ECOWAS.

One of the officials later died of the disease but the other evaded detection to travel to Port Harcourt, where he fell ill and was treated in secret at a city hotel room by medical doctor Ike Enemuo from August 1-3.

The ECOWAS official recovered but the WHO said Enemuo continued to treat patients at his private clinic and operated on at least two people, despite showing symptoms of Ebola from August 11.

He was taken to hospital on August 13 after his symptoms worsened but before that had “numerous contacts with the community”, including visits from family and friends to celebrate a birth.

In hospital, members of his church visited “to perform a healing ritual said to involve the laying on of hands”, while “the majority” of staff treated him before his death, the WHO said.

“Given these multiple high-risk exposure opportunities, the outbreak of Ebola virus disease in Port Harcourt has the potential to grow larger and spread faster than the one in Lagos,” it added.

There have been three confirmed case of Ebola in Port Harcourt so far, including Enemuo. Seven people have died in Nigeria in total out of 18 confirmed cases.

An elderly woman who was a patient at the hospital where Enemuo was treated died from the disease.

Enemuo’s wife — who is also a doctor — was in an isolation unit in Lagos, while his sister was under quarantine in Port Harcourt, Nigeria’s health minister Onyebuchi Chukwu said on Wednesday.

The WHO said family members, healthcare workers and patients at the hospital where Enemuo was treated were at the most risk with church members who visited him.

Nigeria’s federal government is currently working with its counterparts in Rivers State, the WHO, UN children’s fund UNICEF and Doctors Without Borders (MSF) on emergency measures to contain Ebola.

In addition to a 26-bed isolation facility 25 kilometres (16 miles) east of Port Harcourt, a mobile laboratory is in the city to help diagnose cases.

WHO-trained contact tracing and decontamination specialists are on the ground with burial teams, given that Ebola is transmissible even after death