This was noted in a statement by Communication Manager Collins Boakye-Agyemang in Abuja.
Boakye-Agyemang said that while outbreaks were occurring during the Lassa fever season, in countries where the disease was endemic, climbing speed was a cause for concern.
He said the outbreak affected 16 states in Nigeria, with about 213 confirmed cases; including 42 deaths, which marked a significant increase.
According to him, Nigeria had its worst outbreak of Lassa fever and four health professionals have been infected so far in this latest outbreak.
He noted that WHO was expanding its efforts to support federal authorities, the National Council for Disease Control (NCDC) and the affected Nigerian states in response to the outbreak.
He also said that a major focus was on early detection and confirmation of suspected cases.
He said providing optimal support care and ensuring infection prevention and control measures at designated health facilities in affected states was also a priority.
WHO has intensified its technical assistance and is supporting coordination, enhanced surveillance, epidemiological analysis and risk communication.
WHO is also mobilizing experts to support case management and infection prevention and control.
A total of 12 cases have been confirmed so far in Benin, Guinea, Liberia and Togo, including two deaths, with more suspected cases being investigated.
WHO is assisting health authorities in these countries in tracking contacts and delivering medical and non-medical supplies with technical and financial resources as needed for case management, risk communication and logistics.
We are concerned about the high number of cases so early in the Lassa fever season, which is expected to last another four months.
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WHO is working with health authorities in the five affected countries and will ensure that health professionals have the ability to detect cases and that regional spread of the disease is monitored, he said.
He added that WHO has created a regional coordination mechanism for countries to report any suspected Lassa fever case to expedite the flow of timely information.
He said that would help assess the situation, recommend actions and help organize the assistance.
WHO also reached the six other countries at risk; Burkina Faso, Cameroon, Ghana, Mali, Niger and Sierra Leone, and is supporting prevention and preparedness activities as needed.
WHO will continue to advise all countries in the Lassa fever belt to improve their readiness and response capabilities.
Fever of Lassa.
Especially for early case detection, laboratory confirmation, case management under recommended nursing barrier, risk communication and community involvement.
Lassa fever is an acute viral haemorrhagic disease occurring predominantly in West Africa, following human exposure to the urine or feces of infected Mastomys rats.
More than 80% of the cases of Lassa fever are transmission from rodents to humans. Person-to-person transmission occurs in both community and health settings.
Prevention of Lassa fever is based on promoting good community hygiene to discourage rodents from entering the home.
It could also be storing grains and other foods in rodent-proof containers, disposing of litter away from home.
Also keeping families clean, keeping cats and the safe handling of anyone who has died of the disease.
In health care settings, health professionals should always apply standard precautions for infection prevention and control when caring for patients, he said.