Spatial scale influences the distribution of viral diversity in the eukaryotic virome of the mosquito Culex pipiens

Our knowledge of the diversity of eukaryotic viruses has recently undergone a massive expansion. This diversity could influence host physiology through yet unknown phenomena of potential interest to the fields of health and food production. However, the assembly processes of this diversity remain elusive in the eukaryotic viromes of terrestrial animals. This situation hinders hypothesis-driven tests of virome influence on host physiology. Here, we compare taxonomic diversity between different spatial scales in the eukaryotic virome of the mosquito Culex pipiens. This mosquito is a vector of human pathogens worldwide. The experimental design involved sampling in five countries in Africa and Europe around the Mediterranean Sea and large mosquito numbers to ensure a thorough exploration of virus diversity. A group of viruses was found in all countries. This core group represented a relatively large and diverse fraction of the virome. However, certain core viruses were not shared by all host individuals in a given country, and their infection rates fluctuated between countries and years. Moreover, the distribution of coinfections in individual mosquitoes suggested random co-occurrence of those core viruses. Our results also suggested differences in viromes depending on geography, with viromes tending to cluster depending on the continent. Thus, our results unveil that the overlap in taxonomic diversity can decrease with spatial scale in the eukaryotic virome of C. pipiens. Furthermore, our results show that integrating contrasted spatial scales allows us to identify assembly patterns in the mosquito virome. Such patterns can guide future studies of virome influence on mosquito physiology.

A Case for Systematic Quality Management in Mosquito Control Programmes in Europe

The recent spread of invasive mosquito species, such as Aedes albopictus and the seasonal sporadic transmission of autochthonous cases of arboviral diseases (e.g., dengue, chikungunya, Zika) in temperate areas, such as Europe and North America, highlight the importance of effective mosquito-control interventions to reduce not only nuisance, but also major threats for public health. Local, regional, and even national mosquito control programs have been established in many countries and are executed on a seasonal basis by either public or private bodies. In order for these interventions to be worthwhile, funding authorities should ensure that mosquito control is (a) planned by competent scientific institutions addressing the local demands, (b) executed following the plan that is based on recommended and effective methods and strategies, (c) monitored regularly by checking the efficacy of the implemented actions, (d) evaluated against the set of targets, and (e) regularly improved according to the results of the monitoring. Adherence to these conditions can only be assured if a formal quality management system is adopted and enforced that ensures the transparency of effectiveness of the control operation. The current paper aims at defining the two components of this quality management system, quality assurance and quality control for mosquito control programs with special emphasis on Europe, but applicable over temperate areas.

West Nile virus infections in France, July to November 2018

Key messages

We describe the most important episode of West Nile Virus transmission identified in humans in France. In 2018, West Nile virus lineage 2 was isolated for the first time in France which might change the epidemiological situation in the country.

Autochthonous chikungunya and dengue fever outbreak in Mainland France, 2010-2018

Background

Aedes albopictus, vector of dengue and chikungunya viruses, is implanted in mainland France, exposing to the risk of autochthonous transmission. Since 2006, epidemiological and entomological surveillance activities aim to prevent or limit the occurrence of autochthonous cases. We aimed to describe episodes of transmission and control measures implemented in order to reflect on surveillance activities.

Methods

We reviewed all publications and documents produced on autochthonous transmission episodes in France and surveillance protocols. We reviewed surveillance activities, investigation methods and control measures implemented.

Results

Between 2010 and 2018, eight episodes of autochthonous dengue fever transmission and three of chikungunya were recorded in mainland France. All of them occurred in the South east of France, between July and October, when vector density was the highest. Transmission areas were limited to single domestic houses located in discontinuous urban areas. Only two episodes happened in two distinct areas. Chikungunya episodes led to 31 cases and dengue fever episodes to 23 cases. Most cases were identified by door-to-door investigations set-up in transmission areas. We isolated serotypes 1 and 2 for dengue and East Central South Africa lineage for chikungunya in autochthonous cases. Adulticide vector control measures were effective in controlling transmission.

Seven episodes of transmission were due to failure in identifying primary imported cases. Four episodes occurred because of the absence or the lack of vector controls measures around primary imported cases.

Conclusions

Surveillance activities, and autochthonous cases investigations, were effective in limiting the extent of transmission, but were highly demanding for surveillance actors. Identified causes of transmission highlight the need of regular awareness campaigns targeting physicians and biologists.

Key messages

Effectiveness of the surveillance system of dengue, chikungunya and zika viruses, and autochthonous cases investigations. Needs of awareness and training courses targeting health professionals to the risk represented by these viruses.

Chikungunya outbreak in Montpellier, France, September to October 2014

In October 2014, an outbreak of 12 autochthonous chikungunya cases, 11 confirmed and 1 probable, was detected in a district of Montpellier, a town in the south of France colonised by the vector Aedes albopictus since 2010. A case returning from Cameroon living in the affected district was identified as the primary case. The epidemiological investigations and the repeated vector control treatments performed in the area and around places frequented by cases helped to contain the outbreak. In 2014, the chikungunya and dengue surveillance system in mainland France was challenged by numerous imported cases due to the chikungunya epidemic ongoing in the Caribbean Islands. This first significant outbreak of chikungunya in Europe since the 2007 Italian epidemic, however, was due to an East Central South African (ECSA) strain, imported by a traveller returning from West Africa. Important lessons were learned from this episode, which reminds us that the threat of a chikungunya epidemic in southern Europe is real.