“The total number (of suspected cases) reported is 86 and 40 deaths, with a mortality rate of 43.2 percent,” Adewole told a news conference in the capital, Abuja.
The minister said that so far, laboratory tests have confirmed that 22 of the 86 suspected cases were Lassa fever and results were expected on the remainder.
Seven of the affected states include; Bauchi, Nasarawa, Niger, Taraba, Kano, Plateau and Gombe, while the remaining three are in the south, Rivers, Edo and Oyo, he added.
The first case of the disease was recorded last November in Bauchi state. Cases were then reported in Kano and elsewhere.
According to the WHO, Lassa fever is an acute haemorrhagic illness which belongs to the arenarvirus family of viruses, which also includes the Ebola-like Marburg virus.
People with Lassa fever do not display symptoms in 80 percent of cases but it can cause serious symptoms and death in the remainder.
The virus, which is endemic in rodents in West Africa, is transmitted to humans by contact with food or household items contaminated with the animals’ faeces and urine.
Person-to-person contact is also possible through bodily fluids, particularly in hospitals when adequate infection control measures are not taken.
The number of Lassa fever infections in West Africa every year is between 100,000 to 300,000, with about 5,000 deaths, according to the US Centers for Disease Control and Prevention.
Adewole said recorded cases of Lassa fever in Nigeria peaked in 2012 at 1,723 with 112 fatalities but rates have declined since then.
In the latest outbreak, the minister said “most of the cases that we recorded are not through person-to-person contact” but the number of deaths was “unusual”.
He expressed concern about disease notification systems, particularly in Niger state, where “unusual” deaths in August were not reported for up to four months.
Authorities in Lagos, Nigeria’s most populous city of more than 20 million people, on Thursday alerted residents on the need to observe proper hygiene to curb the spread of the disease.
Lagos state, in the southwest, is some 80 kilometres (50 miles) from Oyo state, where suspected cases have been reported.