Understanding malaria transmission in Angola: first detection of Plasmodium malariae in Anopheles spp . and the role of secondary vectors in the Balombo region, Benguela Province

Résumé

Abstract Background Angola is one of the most affected countries in sub-Saharan Africa and was off-track to meet the WHO Global Technical Strategy targeting of a 75% reduction in malaria incidence and mortality by 2025. Recent studies highlighted major knowledge gaps regarding malaria vectors in Angola, particularly secondary vectors. A malaria control project initiated in 2007 in Balombo (Benguela Province, central Angola) has monitored malaria dynamics for 18 years, revealing increased Plasmodium prevalence and more frequent detection of non-falciparum species, mainly Plasmodium malariae (in co-infection with P. falciparum ) in villagers of the Balombo region. This study aimed to characterize Anopheles populations in this region by assessing species composition, behavioural patterns, and infection rate. And to a less extent, to compare the performance of two indoor and outdoor mosquito trapping methods. Methods Surveys were conducted during the rainy (December 2023 and 2024) and dry seasons (July 2024) in villages around the town of Balombo. Adult mosquitoes were collected indoors and outdoors using CDC Light Traps and BG-Pro traps in randomly selected houses. Female Anopheles were morphologically and molecularly identified. Primary and secondary vectors were screened for Plasmodium spp . using qPCR-high resolution melting, and positive samples were sequenced. Results A strong seasonal effect was observed in Anopheles populations, with higher abundance, diversity, and Plasmodium - infection rates during the rainy season. An. funestus remained the main vector, but Plasmodium spp. was also detected in five other species: An. arabiensis , An. gambiae , An. marshallii , An. rufipes , and An. maculipalpis . This is the first report of P. malariae in Anopheles mosquitoes and the first mention of the role of secondary vectors in malaria transmission in Benguela Province. Conclusion This study provides a thorough and updated inventory of Anopheles species in the Balombo region. Molecular biology confirmed the presence of P. falciparum and P. malariae in several species of Anopheles underscoring the existence of a complex transmission system in villages of Balombo. Infected exophagic and exophilic Anopheles species, exhibiting opportunistic behaviour, likely contribute, as secondary vectors, to the increase of Plasmodium spp. transmission in the study sites. Therefore, confirming the need to implement complementary interventions targeting outdoor malaria transmission. Author Summary This study provides a thorough and updated inventory of Anopheles species in the Balombo region, conducted nearly two decades after the implementation of vector control interventions, in a setting where LLINs continue to be distributed. Sequencing confirmed the presence of Plasmodium spp. in Anopheles during both the dry and rainy seasons and revealed the first detection of P. malariae in mosquitoes collected in Angola. Although An. funestus remains the primary malaria vector in the Balombo region, the detection of Plasmodium spp. in five other Anopheles species highlights the existence of a more complex transmission system across the studied villages. While the sampling protocol and the relatively low numbers of An. funestus captured in some villages preclude definite conclusions regarding its behaviour, the possibility of a shift towards exophagy and exophily in some villages of Balombo is possible. It is therefore necessary to step up regular entomological surveillance, particularly in villages that were the focus of vector control campaigns between 2007 and 2011. Moreover, the detection of Plasmodium spp. in several secondary vectors exhibiting opportunistic and exophilic behaviours, such as An. marshallii , suggests that LLIN coverage alone may be insufficient to prevent exposure to infectious mosquito bites. A comprehensive assessment of LLINs use throughout the year is therefore needed, together with the adaptation of vector control strategies to address the contribution of exophilic vectors to malaria transmission in the villages of Balombo.

Citer ce document

Accès au document

Texte intégral en lecture en ligne, réservé aux abonnés SPHAERO et aux membres de l'institution. Se connecter

Auteur(s)

Statistiques

Consultations : 1

Téléchargements : 0