Health officials across Africa are racing to determine how Nigeria’s first Ebola patient in more than a decade became infected, amid fears the outbreak could spread further after reaching a fourth African country.

The Swiss foreign ministry said on Friday the patient in Nigeria, the Ugandan-born wife of a Swiss diplomat based in Abuja, had not travelled to the Democratic Republic of Congo, where the outbreak was first detected in mid-May before spreading to Uganda, Kenya and now Nigeria. The woman was believed to have contracted Ebola while travelling with her husband in Uganda, the ministry added.

The new information contradicts accounts from Uganda, which previously said the woman had travelled to eastern DR Congo, and will raise concerns about the ability of authorities to contain the outbreak, which is already the most geographically widespread in history.

The Ugandan government reported Ebola cases in May and June before WHO declared it Ebola-free in August. A Ugandan government spokesperson told Reuters on Thursday that Uganda had no Ebola cases and that, if it did, it would make that information public.

The World Health Organization said investigations were continuing to establish the likely source of infection for the Ebola patient in Nigeria.

The Africa Centres for Disease Control and Prevention is investigating whether the patient may have come into contact with an Ebola patient in Kenya, as both travelled from Uganda’s Entebbe airport on 3 October, said Dr Wessam Mankoula, head of emergency preparedness and response at the organisation.

Catherine Smallwood, a WHO Ebola incident manager in DR Congo, told a UN briefing in Geneva via video link on Friday that WHO staff in DR Congo had no information showing the patient in Nigeria had travelled to the country.

Smallwood said a link to the case in Kenya was possible, but added that officials would need to compare the timing with when the Nigeria patient’s symptoms began to tell whether the infection more likely happened at the Ugandan airport or elsewhere.

Marion Koopmans, a Dutch virologist and member of the WHO’s Ebola emergency committee, cast doubt on the theory. “I think that is very speculative unless there is evidence of sharing the same space in a manner that could explain that,” she said. “Random presence at the same location, a large airport, is not a supported epidemiological link by any standard of what we currently know.”The Nigerian health minister, Muhammad Ali Pate, said Nigeria’s case remains contained and that contact-tracing was continuing.

“We are trying to contain it so it doesn’t go out to the communities. Hopefully, it won’t get to that and we are working hard to ensure that,” Pate said.

Melaku Yirga, vice-president for Africa at Prosper Global (formerly Mercy Corps), said the confirmation of Ebola in Kenya and Nigeria reinforces the need for countries to work closely together to prevent further transmission.

“What matters most now is speed, sharing information across borders without delay and ensuring frontline health workers and local organiaations have the resources to respond quickly,” he said.

Ebola is a highly contagious and often fatal viral disease that affects humans and non-human primates. It spreads through body fluids or contaminated materials and causes organ damage, blood vessel impairment and sometimes severe internal and external bleeding.

The current outbreak is caused by the rare Bundibugyo virus, which has no approved treatment or vaccine. It was first announced on 15 May and has infected more than 9,500 people and killed nearly half of them.

The outbreak is the largest and deadliest in DR Congo’s history and second only globally to the 2014-16 outbreak in west Africa, which infected more than 28,600 people and killed more than 11,000.