Nigeria's Lassa Fever Outbreak - Epi Week 10

Credit CDC

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It's been six weeks since we last checked in on Nigeria's Lassa fever epidemic, and while the outbreak appeared to have peaked relatively early in February, over the past couple of weeks Nigeria's CDC has reported a resurgence in cases.

Lassa fever is a Viral Hemorrhagic Fever (VHF) endemic to a handful of West African nations and is among the diseases the World Health Organization included in last year's List Of Blueprint Priority Diseases, for which there is an urgent need for additional research and drug development.

• Crimean-Congo haemorrhagic fever (CCHF)
• Ebola virus disease and Marburg virus disease
• Lassa fever
• Middle East respiratory syndrome coronavirus (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS)
• Nipah and henipaviral diseases
• Rift Valley fever (RVF)
• Zika
• Disease X

The virus is commonly carried by multimammate rats, a local rodent that often likes to enter human dwellings. Exposure is typically through the urine or dried feces of infected rodents, and roughly 80% who are infected only experience mild symptoms.

The incubation period runs from 10 days to 3 weeks, and the overall mortality rate is believed to be in the 1%-2% range, although it runs much higher (15%-20%) among those sick enough to be hospitalized.  

Like many other hemorrhagic fevers, person-to-person transmission may occur with exposure to the blood, tissue, secretions, or excretions of an individual (cite CDC Lassa Transmission).

Based the latest report from Nigeria's CDC, hopes for an early end to this year's Lassa epidemic (see NCDC report Decline in Lassa Fever Cases as NCDC Sustains Intensive Response) now appear in doubt.

2019 LASSA FEVER OUTBREAK SITUATION  

EPI Week 10
10 th March 2019

HIGHLIGHTS

• In the reporting Week 10 (4 th - 10 th March, 2019) 52 new confirmed i cases were reported from eight states - Edo(23), Ondo(11), Ebonyi (9), Bauchi(1), Nasarawa(2), Plateau(1), Taraba (4) and Delta (1) with eleven new deaths in Edo (3), Ondo(3), Ebonyi (4) and Nasarawa (1) States.

• From 1 st January to 10 th March, 2019, a total of 1752 suspected i cases have been reported from states. Of these, 472 were confirmed positive, 15 probable and 1265 negative (not a case)-Table 1.

• Since the onset of the 2019 outbreak, there have been 110* deaths in confirmed cases. Case fatality ratio in confirmed cases is 23.3% -Table 1
   
• Twenty-one (21) States (Edo, Ondo, Bauchi, Nasarawa, Ebonyi, Plateau, Taraba, FCT, Adamawa, Gombe, Kaduna, Kwara, Benue, Rivers, Kogi, Enugu, Imo, Delta, Oyo, Kebbi and Cross River) have recorded at least one confirmed case across 73 Local Government Areas- Table 1, Figure 1
   
• In the reporting week 10, no new health care worker was affected. A total of fifteen health care workers have been infected since the onset of the outbreak in seven States – Edo (7), Ondo (3), Ebonyi (1), Enugu (1), Rivers (1), Bauchi (1) and Benue (1) with two deaths in Enugu and Edo
   
• Sixty-eight (68) patients are currently being managed at various treatment centres across the country: Irrua Specialist Teaching Hospital(ISTH) treatment Centre (33), Federal Medical Centre Owo (16), Federal Teaching Hospital Abakaliki (10), Bauchi (1), Plateau (3), Nasarawa(1) and Taraba (4) - Table 1
   
• A total of 5340 contacts have been identified from 20 States. Of these 2129 (39.9%) are currently being followed up, 3158 (59.1%) have completed 21 days follow up, while 4(0.1%) were lost to follow up. 82(1.5%) symptomatic contacts have been identified, of which 49 (1.0%) have tested positive -Table 1
   
• Multi sectoral one health national rapid response teams (NCDC, NFELTP, Federal Ministry of Agricultural and Federal Ministry of Environment) deployed to high burden states
   
• National Lassa fever multi-partner, multi-sectoral Emergency Operations Centre(EOC) continues to coordinate the response activities at all levels

While primarily a regional threat, during their last major outbreak (2016) exported cases turned up in several countries, including Germany and Sweden (see Germany's RKI Statement On Lassa Fever Cluster In Cologne & WHO Lassa Fever Update - Sweden (Imported)).

In 2016 the ECDC published a Rapid Risk Assessment on the spread of Lassa Fever out of  West Africa.  While the risk of seeing Lassa Fever outside of West Africa was determined to be low, they authors wrote:

The two imported cases of Lassa fever recently reported from Togo indicate a geographical spread of the disease to areas where it had not been recognised previously. Delays in the identification of viral haemorrhagic fevers pose a risk to healthcare facilities.

Therefore, Lassa fever should be considered for any patient presenting with suggestive symptoms originating from West African countries (from Guinea to Nigeria) particularly during the dry season (November to May), a period of increased transmission, and even if a differential diagnosis such as malaria, dengue or yellow fever is laboratory-confirmed.

A reminder that in this increasingly interconnected and mobile world that localized outbreaks - no matter how remote - aren't guaranteed to remain such, and that without a proactive response they can very quickly turn into public health threats anywhere in the world.