Friday, February 12, 2016

WHO Update : Yellow Fever Outbreak In Angola


Over the past couple of days there have been media reports of another arbovirus outbreak in west central Africa (see Yellow fever outbreak kills 37 in Angola) vectored by the same mosquito as the Zika (and Dengue & CHKV) virus.

Yellow fever is currently a threat to 900 million inhabitants of Africa and parts of South America where it remains endemic and occasionally epidemic.

First the WHO update on the Angola outbreak, and then I'll return with a bit more on the subject.

Yellow Fever – Angola

On 21 January 2016, the National IHR Focal Point of Angola notified WHO of an outbreak of yellow fever. 

The first cases were identified in the district of Viana (Luanda province) on 5 December 2015. Yellow fever infection was initially confirmed in three patients by polymerase chain reaction at the Zoonosis and Emerging Disease Laboratory of the National Institute for Communicable Diseases in Johannesburg, South Africa and at the Pasteur Institute in Dakar, Senegal. 

As of 8 February, a total of 164 suspected cases and 37 deaths had been reported in Angola. The majority of cases (n=138) had been reported in the province of Luanda. Other affected provinces include Cabinda, Cuanza Sul, Huambo, Huila and Uige. Suspected cases are undergoing laboratory testing in order to rule out other aetiologies and cross reactions with yellow fever.

Public health response

The national task force has been activated to control the outbreak. Health authorities in Angola are implementing a number of control and response activities, including coordination, clinical case management, enhanced surveillance, laboratory testing, social mobilization and vector control. Epidemiological and entomological investigations are ongoing in the main affected areas. On 3 February, the first round of immunization campaign started in Luanda. 

WHO has deployed three experts to provide operational support. In addition to financial support, technical directives and guidelines have been shared with country officials to improve the quality of the response.

On 2 February, an immunization campaign was launched in Luanda. The campaign will initially cover a target population of 1,578,085 in Viana.

WHO risk assessment

In the affected districts of Luanda, there is a high density of Aedes Aegypti, the primary vector of yellow fever; consequently, the risk of spread to unaffected districts is high. This risk is further exacerbated by the high proportion of susceptible individuals, as the only protected groups are the citizens with international vaccination cards and those children that have been vaccinated against yellow fever since 2008. WHO continues to monitor the epidemiological situation and conduct risk assessment. WHO does not recommend any travel or trade restriction to Angola based on the current information available.


Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. Up to 50% of severely affected persons without treatment will die from yellow fever. There are an estimated 130,000 cases of yellow fever reported yearly, causing 44,000 deaths worldwide each year, with 90% occurring in Africa. There is no specific treatment for yellow fever. Treatment is symptomatic, aimed at reducing the symptoms for the comfort of the patient. Vaccination is the most important preventive measure against yellow fever. Since the second half of 2015, yellow fever virus circulation has been reported in Mali and Ghana.

While Yellow Fever has been successfully eradicated from North America and Europe for decades, the mosquito vectors that transmit the virus are still present in some regions.
And just as with Dengue, Chikungunya, Malaria,  and most recently Zika, the potential for limited re-introduction of Yellow Fever is not nil.  

A 2010 Eurosurveillance Journal devoted an entire issue to The Threat Of Vector Borne Diseases, including making the case for the reintroduction of  Yellow fever and dengue: a threat to Europe? by P Reiter (excerpt below).

Yellow fever and dengue: a threat to Europe?

The introduction and rapidly expanding range of Aedes albopictus in Europe is an iconic example of the growing risk of the globalisation of vectors and vector-borne diseases. The history of yellow fever and dengue in temperate regions confirms that transmission of both diseases could recur, particularly if Ae. aegypti, a more effective vector, were to be re-introduced.  The article is a broad overview of the natural history and epidemiology of both diseases in the context of these risks.


The history of dengue and yellow fever in Europe is evidence that conditions are already suitable for transmission. The establishment of Ae. albopictus has made this possible, and the possibility will increase as the species expands northwards, or if Ae. aegypti is re-established.

And in 2013 Peter Hotez - Dean of the National School of Tropical Medicine at Baylor College of Medicine - and Kristy Murray, an associate professor of pediatrics at Baylor College of Medicine who studys mosquito-borne diseases, penned a PLoS Blog entitled.  
Peter Hotez and Kristy Murray from Baylor College of Medicine highlight the potential for yellow fever to return to the southern cities of the United States

Spolier alert, it could.

A reminder, that when it comes to re-emerging infectious diseases - even in areas that for decades have been immune - one should never say `never'.