Lack of robust evidence for a Wolbachia infection in Anopheles gambiae from Burkina Faso

Revisiting Wolbachia detections: Old and new issues in Aedes aegypti mosquitoes and other insects

Wolbachia continue to be reported in species previously thought to lack them, particularly Aedes aegypti mosquitoes. The presence of Wolbachia in this arbovirus vector is considered important because releases of mosquitoes with transinfected Wolbachia are being used around the world to suppress pathogen transmission and these efforts depend on a lack of Wolbachia in natural populations of this species. We previously assessed papers reporting Wolbachia in natural populations of Ae. aegypti and found little evidence that seemed convincing. However, since our review, more and more papers are emerging on Wolbachia detections in this species. Our purpose here is to evaluate these papers within the context of criteria we previously established but also new criteria that include the absence of releases of transinfections within the local areas being sampled which has contaminated natural populations in at least one case where novel detections have been reported. We also address the broader issue of Wolbachia detection in other insects where similar issues may arise which can affect overall estimates of this endosymbiont more generally. We note continuing shortcomings in papers purporting to find natural Wolbachia in Ae. aegypti which are applicable to other insects as well.

Limited association between Wolbachia and Plasmodium falciparum infections in natural populations of the major malaria mosquito Anopheles moucheti

Since the discovery of natural malaria vector populations infected by the endosymbiont bacterium Wolbachia, a renewed interest has arisen for using this bacterium as an alternative for malaria control. Among naturally infected mosquitoes, Anopheles moucheti, a major malaria mosquito in Central Africa, exhibits one of the highest prevalences of Wolbachia infection. To better understand whether this maternally inherited bacterium could be used for malaria control, we investigated Wolbachia influence in An. moucheti populations naturally infected by the malaria parasite Plasmodium falciparum. To this end, we collected mosquitoes in a village from Cameroon, Central Africa, where this mosquito is the main malaria vector. We found that the prevalence of Wolbachia bacterium was almost fixed in the studied mosquito population, and was higher than previously recorded. We also quantified Wolbachia in whole mosquitoes and dissected abdomens, confirming that the bacterium is also elsewhere than in the abdomen, but at lower density. Finally, we analyzed the association of Wolbachia presence and density on P. falciparum infection. Wolbachia density was slightly higher in mosquitoes infected with the malaria parasite than in uninfected mosquitoes. However, we observed no correlation between the P. falciparum and Wolbachia densities. In conclusion, our study indicates that naturally occurring Wolbachia infection is not associated to P. falciparum development within An. moucheti mosquitoes.

Screening of natural Wolbachia infection in mosquitoes (Diptera: Culicidae) from the Cape Verde islands

BACKGROUND

Wolbachia pipientis is an endosymbiont bacterium that induces cytoplasmic incompatibility and inhibits arboviral replication in mosquitoes. This study aimed to assess Wolbachia prevalence and genetic diversity in different mosquito species from Cape Verde.

METHODS

Mosquitoes were collected on six islands of Cape Verde and identified to species using morphological keys and PCR-based assays. Wolbachia was detected by amplifying a fragment of the surface protein gene (wsp). Multilocus sequence typing (MLST) was performed with five housekeeping genes (coxA, gatB, ftsZ, hcpA, and fbpA) and the wsp hypervariable region (HVR) for strain identification. Identification of wPip groups (wPip-I to wPip-V) was performed using PCR-restriction fragment length polymorphism (RFLP) assay on the ankyrin domain gene pk1.

RESULTS

Nine mosquito species were collected, including the major vectors Aedes aegypti, Anopheles arabiensis, Culex pipiens sensu stricto, and Culex quinquefasciatus. Wolbachia was only detected in Cx. pipiens s.s. (100% prevalence), Cx. quinquefasciatus (98.3%), Cx. pipiens/quinquefasciatus hybrids (100%), and Culex tigripes (100%). Based on the results of MLST and wsp hypervariable region typing, Wolbachia from the Cx. pipiens complex was assigned to sequence type 9, wPip clade, and supergroup B. PCR/RFLP analysis revealed three wPip groups in Cape Verde, namely wPip-II, wPip-III, and wPip-IV. wPip-IV was the most prevalent, while wPip-II and wPip-III were found only on Maio and Fogo islands. Wolbachia detected in Cx. tigripes belongs to supergroup B, with no attributed MLST profile, indicating a new strain of Wolbachia in this mosquito species.

CONCLUSIONS

A high prevalence and diversity of Wolbachia was found in species from the Cx. pipiens complex. This diversity may be related to the mosquito's colonization history on the Cape Verde islands. To the best of our knowledge, this is the first study to detect Wolbachia in Cx. tigripes, which may provide an additional opportunity for biocontrol initiatives.