LAGOS, July 13 -- Lagos, the most populous region in southwestern Nigeria, will remain on alert to prevent the fatal Ebola virus from entering the state, the country's Commissioner for Health Jide Idris said on Sunday.

In a statement reaching Xinhua, the health commissioner advised the public to observe personal and environmental hygiene as part of precautionary measures to prevent the outbreak of Ebola disease in the state.

He said the advice was necessary because of the increase in the number of cases and deaths caused by the disease in some neighboring West African countries such as Guinea, Liberia and Sierra Leone.

The commissioner said that presently there was no specific treatment for the disease, which could be transmitted in the course of feeding, holding and caring for victims.

Fruits and bats are considered to be the natural host of the virus, he added.

The Ebola virus, which can incubate for up to 21 days, has a fatality rate of up to 90 percent.

The virus was first discovered in 1976 in two simultaneous outbreaks in Sudan and in the Democratic Republic of the Congo (DRC), taking its name from the Ebola River where the DRC outbreak was found in a nearby village.

The World Health Organization (WHO) defines the disease, formerly known as Ebola hemorrhagic fever, as "a severe, often fatal illness" and "one of the world's most virulent diseases."

The city of Lagos is the most populous in Nigeria with a population of about 20 million, and it is also the second fastest-growing city in Africa.