* Man collapsed at Lagos international airport
* Lagos is a city of 21 million people
* Ebola has killed 660 people across West Africa
By Chijioke Ohuocha
LAGOS, July 24 (Reuters) - A Liberian man is being tested for the deadly Ebola virus after he collapsed on arrival at an airport in Nigeria's commercial capital Lagos, a mega-city of 21 million people, the Lagos State Health Ministry said on Thursday.
Ebola has killed 660 people across Guinea, Liberia and Sierra Leone since it was first diagnosed in the region in February, straining their impoverished healthcare systems.
If confirmed, the case would be the first on record of one of the world's deadliest diseases in Nigeria, Africa's biggest economy and, with 170 million people, its most populous country.
The special adviser on public health to the Lagos state government, Yewande Adeshina, told a news conference the man, who is in his 40s, arrived at Lagos airport from Liberia on Sunday. He was rushed to hospital and put in an isolation ward, she said.
"The patient was admitted and detained on suspicion of possible EBV (Ebola virus) infection, while blood sample collection and testing was initiated," she said. The test results were pending, she said.
A spokesman for the World Health Organisation (WHO) in Geneva confirmed one suspected case of Ebola in Nigeria and said samples had been sent to a WHO lab for testing.
Adeshina said Lagos state authorities had requested the flight's manifest to contact the other passengers. They would also trace the man's travel route and had already distributed protective clothing to health workers, she said.
Ben Neuman, a virologist and Ebola expert at Britain's University of Reading, said it was important to note that Ebola is one of a number of viruses that can cause haemorrhagic fever, and that others, including Lassa fever virus and Dengue virus, could turn out to be the diagnosis in this case.
"Some of these other, more common haemorrhagic fever viruses have already been the cause of false alarms in the ongoing west African Ebola outbreak," Neuman told Reuters in London, urging calm.
HEALTH WORKERS AT RISK
Nigeria has some of the continent's least adequate healthcare infrastructure, despite access to billions of dollars of oil money as Africa's biggest producer of crude.
The Ebola outbreak started in Guinea's remote southeast and has since spread, aided by a lack of information about the disease and affected communities' suspicion of emergency medical staff.
A recent wave of infections among medical personnel is raising questions about the preparedness of regional health structures.
Sierra Leone announced on Wednesday that Sheik Umar Khan, the doctor leading the fight against Ebola in the country, had himself contracted the disease following the deaths of several nurses at the treatment centre where he works.
Dozens of nurses at the centre staged a sit-down strike this week, calling for management of the government-run facility to be transferred to medical charity Medecins Sans Frontieres (MSF).
"If you have that number of health personnel being infected within a relatively short period of time, there is definitely something wrong with the system," Deputy Health Minister Abu Bakarr Fofanah said on Thursday.
He said Khan was responding well to treatment, however.
There is no cure or vaccine for Ebola, which causes diarrhoea, vomiting and internal and external bleeding and can kill up to 90 percent of those infected, although the mortality rate of the current outbreak is around 60 percent. (Additional reporting by Kate Kelland in London and Umaru Fofana in Freetown; Writing by Tim Cocks and Joe Bavier; Editing by Jeremy Gaunt, Larry King and Sonya Hepinstall)