German Travelers Bringing Diverse Dengue Strains Home

German travelers are bringing home a disturbingly diverse array of dengue virus (DENV) strains according to recently-published information from the Centers for Disease Control and Prevention (CDC)’s Emerging Infectious Diseases Journal (EID).

The authors of the study noted that a number of countries in Southeast Asia considered “DENV-hyperendemic,” are “increasingly popular tourist destinations for residents of Germany. Thus, German travelers to these countries are potentially exposed to multiple types and genotypes of DENV.” Travel to two countries in particular, Philippines and Indonesia, represent an increasing threat to German tourists because these popular destinations have a “much higher…comparative risk of infection with travel-associated DENV.” In the Philippines, the risk of infection was 10%, and in Indonesia, 12%. The scientists emphasized that they did not factor in seasonal fluctuations and travel patterns that might affect DENV incidence among German travelers.

The team analyzed 15,876 acute-phase serum samples obtained from patients whose doctors suspected that they might have a DENV infection. Those samples were obtained between 2006 and 2015 as part of a World Health Organization (WHO) collaboration to aid research and diagnostic testing. The group analyzed the samples, isolating DENV and extracting viral RNA. In total, they “successfully isolated 70 DENV strains originating from 20 countries,” with the majority of the DENV infections originating in Thailand (35.7%), Indonesia (12.8%), and the Philippines (10%). Travelers to India accounted for 7.1% of the DENV infections, while no other country in Asia, Africa, or the Americas contributed more than 4.3% of the total infections.

While a number of strains of the virus were evident in the samples, the team was troubled by not only “a high genetic diversity of DENV genotypes and lineages,” but also by the development that two of the lineages (DENV-3, genotype III, lineage 6 and DENV-4, genotype III, lineage 6) seem to be extremely recent developments. The researchers noted that these two lineages “are still responsible for outbreaks in countries in Southeast Asia.” The great diversity of DENV strains detected “supports the hypothesis of multiple geographic origins or extensive virus interchange,” they added.

Although there are myriad strains of dengue, there are four main serotypes, or variations, of the virus, known as DEN-1, DEN-2, DEN-3, and DEN-4. An individual who is infected with one serotype and recovers from the illness will usually be immune to that serotype; however, the individual will not necessarily be immune to the other serotypes although they may experience partial and/or temporary immunity. Furthermore, someone who is immune to one serotype but becomes infected subsequently with another serotype is more likely to develop severe dengue, which is also known as Dengue Hemorrhagic Fever (DHF). In some areas of the world, such as Philippines, DHF is one of the leading causes of death.

At present, the CDC has not issued any travel health notices regarding DENV for any specific countries, and the German research team also did not issue any specific warnings other than to emphasize “the need for continued surveillance of DENV infections…as well as prompt and rapid serologic and molecular testing for DENV infection in febrile patients returning from DENV-endemic countries.”

A CDC spokesperson noted that the best way to avoid contracting a dengue infection is to “avoid mosquito bites if you live in or travel to an endemic area.” They recommended avoiding and eliminating places where mosquitoes might lay eggs, such as outdoor water containers, and using insect repellent to prevent mosquito bites. “When possible, wear long sleeves and pants for additional protection, and make sure window and door screens are secure and without holes,” they said. They added that if you are in proximity to someone who may have dengue, it is important to prevent mosquitoes from biting that person, since the insects can contract and then spread the disease after biting the infected individual.