Analysis of two imported cases of yellow fever infection from Ivory Coast and The Gambia to Germany and Belgium

Background: yellow fever remains one of the great burdens for public health in the endemic regions in Africa and South America. The under reporting of yellow fever cases in the respective regions and lack of international interest leads to an underestimation of the constant danger in these areas. Non-vaccinated travelers take a high risk without the effective protection of YFV 17D vaccination.

Objectives: Two YF cases were imported to Europe in the last 4 years. We characterized two yellow fever virus (YFV) isolates from severely infected patients coming back from Africa, Ivory Coast and The Gambia, by genome sequencing and phylogenetic analysis.

Study design: The virus infections in different organs were analyzed with pathological, immunohistological, electronmicroscopical and quantitative real-time PCR methods.

Results and Conclusion: High virus loads in spleen and liver (2.4 x 10(6) to 3 x 10(7) GE/mL) demonstrated by real time PCR show massive virus replication leading to extraordinary progression of the disease in these patients. Immunohistological and electron microscopical analysis confirms virus particles in liver tissue. In all other organs no virus could be detected. A fast, specific and sensitive virus PCR detection is recommended for diagnostic of acute infections. The further sequence alignments show that the new isolates belong to the type II West African strain with great homology to over 40-year old YF isolates from Senegal and Ghana. The divergence observed was on average 3.3%, ranging from 0.0% to 5.0% in the coding region of Gambia2001 strain and 2.9%, ranging from 0.0% to 4.3% in the coding region of the IvoryC1999 strain. Most mutations (5.0%/4.3%, respectively) occurred in the envelope protein.