T.I Olasoju1,2, M.I. Olasoju3, B. Dagash1,4, B.B Abaye1, C. Enumah1, S. Isah1,5, M.T Bolori6, O.O. Adebowale3

  1. Nigeria Field Epidemiology and Laboratory Training Program (NFELTP).
  2. Department of Veterinary and Pest Control Services, Federal Ministry of Agriculture and Rural Development, Garki, Abuja, FCT, Nigeria.
  3. Department of Veterinary Public Health and Preventive Medicine, Federal University of Agriculture, Abeokuta, Ogun State, Nigeria
  4. Department of Medical Microbiology, University of Maiduguri Teaching Hospital, Maiduguri, Borno State,Nigeria.
  5. Bauchi State Primary Health Care Development Agency, Bauchi, Bauchi State, Nigeria.
  6. Department of Community Medicine, University of Maiduguri, Maiduguri, Borno State, Nigeria.


Introdution: Lassa fever is a viral hemorrhagic disease caused by the Lassa virus, a single stranded RNA virus of the Arenavirus family. It is a zoonotic illness spread by rats of the species Mastomys natalensis. Between weeks 1 and 17, (2017), 242 suspected Lassa fever cases were reported in Nigeria, with 58 laboratory confirmed cases and 46 fatalities (CFR, 19.01%) from 50 Local Government Areas (LGAs) in 20 States.

Methods: We conducted an outbreak investigation and gathered a thorough clinical history of the index case as well as contacts, who were then followed up using the standard viral hemorrhagic fever contact monitoring form. Following that, blood samples were collected from this patient. A total of 54 contacts were tracked for 21 days and their temperatures were recorded using a clinical thermometer. Furthermore, an environmental evaluation of the Zabarmari community and the Madinatu Internally-displaced persons’ (IDP) camp was carried out.

Results: The index case was a 32-year-old woman who was internallydisplaced in Zabarmari community. Her symptoms began with fever and vaginal bleeding and progressed to bleeding from the nose, mouth, and urethra. There was a history of rat exposure as well as inadequate environmental sanitation and hygiene. Real Time PCR detected Lassa fever in the blood sample. The Borno State Ministry of Environment, in partnership with the Ministry of Health, undertook public health education on Lassa fever prevention and implemented excellent sanitary measures.

Conclusion: Increased awareness creation on good infection prevention and control practices is crucial among internally-displaced person and health care providers to prevent occurrence and spread of the disease.

Keywords: Lassa fever, Viral haemorrhagic fever, Index case, Mastomys natalensis.


Dr. M.I. Olasoju
Department of Veterinary Public Health
and Preventive Medicine,
Federal University of Agriculture,
Abeokuta, Ogun State,
Submission Date: 6th Nov., 2023
Date of Acceptance: 1st April, 2024
Publication Date: 30th April, 2024


Lassa fever is an acute viral hemorrhagic fever, first reported in 1969 in Lassa town of Borno State, NorthEast Nigeria. It is one of Africa’s worst hemorrhagic fevers, prevalent in West Africa, and affects 100,000- 500,000 people every year, with a fatality rate of 15%- 20%.1
Lassa fever is a zoonotic illness caused by the Arena viridae virus family, with the virus containing a single stranded RNA genome and measures 110 to 130nm in diameter. Rodents of the Mastomys natalensis species complex act as viral reservoirs, eliminating the virus via saliva, urine, excreta, and other bodily fluids. Man becomes infected by ingesting foodstuffs contaminated with these fluids.2 Lassa fever is an acute viral hemorrhagic fever that was first reported in 1969 in Lassa village, Borno State, Nigeria. It is one of Africa’s worst hemorrhagic fevers, prevalent in West Africa, and affects 100,000-500,000 people every year, with a fatality rate of 15%-20%.1

Lassa fever affects people of all ages and both sexes, according to the World Health Organization (WHO).7 People living in rural areas, particularly those with inadequate sanitation or congested living circumstances, and where Mastomys spp. are prevalent, are more at risk of infection. Similarly, health professionals who care for sick Lassa fever patients without suitable or enough personal protective equipment and infection control methods increase their risk of contracting the deadly virus.
Lassa fever samples from laboratories are potentially hazardous and should be treated with extreme caution. Lassa virus infections may only be definitively detected in reference laboratories utilizing tests like the Reverse
Transcription-Polymerase Chain Reaction (RT-PCR) assay, Antibody Enzyme-linked Immunosorbent Assay (ELISA), Antigen Detection Tests, and Virus Isolation by Cell Culture.7

The Lassa virus can be found in blood at an early stage of the illness. Death occurs around two weeks following the commencement of disease, with fatal patients exhibiting greater levels of viraemia than survivors.8 The virus is eliminated from circulation in survivors around three weeks after the onset of symptoms.9-11 Only a small percentage of patients produce antibodies to immunoglobulin M (IgM) and immunoglobulin G (IgG) within the first few days of illness, and patients with deadly Lassa fever may not build-up antibodies at all. 9, 11, 12 As a result, Real Time Polymerase Chain Reaction (RT-PCR) is an essential technique for the quick and accurate diagnosis of Lassa fever. 9, 12, 13
When administered intravenously or orally to Lassa fever patients early enough, generally before day 7 of illness, the antiviral medicine Ribavirin, a purine nucleoside with broad-spectrum antiviral characteristics, is extremely effective.14 Best practices in personal and community cleanliness, adequate environmental sanitation to deter rats from entering houses and contaminating foods, and early detection and treatment of cases and contacts are used to accomplish prevention and control. Standardized safety standards in the healthcare context are crucial, especially when dealing with sick patients.

A suspected case of Lassa fever was considered as “any person with gradual onset of one or more of the following: malaise, fever, headache, sore throat, cough, nausea, vomiting, diarrhea, myalgia, chest pain hearing loss and a history of contact with excreta of rodents or with a confirmed case of Lassa fever”. Moreover, a confirmed case was defined as “a suspected case that was laboratory confirmed positive using RT-PCR”. A contact was defined as “a person having close personal contact with a suspected or confirmed case (living with, caring for) or the laboratory staff who tests the specimens of a patient in the 3 weeks after the onset of the illness”.

This study documented a confirmed case of Lassa fever in Borno State, described the demography and spatiotemporal picture of the event and identified possible risk factors. Furthermore, technical assistance was offered to the state in order to improve investigations and disease control.