Seasonal abundance and molecular identification of West Nile virus vectors, Culex pipens and Culex quinquefasciatus (diptera: culicidae) in Abeokuta, South-West, Nigeria

Mosquito (Diptera: Culicidae) populations in contrasting areas of the western regions of Burkina Faso: species diversity, abundance and their implications for pathogen transmission

BACKGROUND

Mosquitoes (Diptera: Culicidae) can have a significant negative impact on human health. The urbanization of natural environments and their conversion for agricultural use, as well as human population growth, may affect mosquito populations and increase the risk of emerging or re-emerging mosquito-borne diseases. We report on the variety and number of adult mosquitoes found in four environments with varying degrees of human impact (rural, urban, rice fields, and forest) located in a savannah zone of West Africa.

METHODS

Mosquitoes were collected from two regions (Hauts-Bassins and Sud-Ouest) of Burkina Faso during five periods between August 2019 and June 2021. Sampling sites were grouped according to environment. Mosquitoes were collected using BG-Sentinel traps and double net traps, and Prokopack Aspirators. Statistical analyses were performed using R software version 4.1.2. Logistic regression, using generalised mixed linear models, was used to test the effect of environment on mosquito abundance and diversity. Alpha diversity analysis was also performed, using the vegan package.

RESULTS

A total of 10,625 adult mosquitoes were collected, belonging to 33 species and five genera: Culex, Aedes, Anopheles, Mansonia, and Ficalbia. The most dominant species were Culex quinquefasciatus, Anopheles gambiae sensu lato and Aedes aegypti. Alpha diversity was similar in the two regions. Habitat had a significant effect on mosquito species richness, the Shannon index and the Simpson index. The rural environment had the highest species richness (n = 28) followed by the forest environment (n = 24). The highest number of mosquitoes (4977/10,625) was collected in the urban environment.

CONCLUSIONS

The species composition of the mosquito populations depended on the type of environment, with fewer species in environments with a high human impact such as urban areas and rice fields. Due to the diversity and abundance of the mosquito vectors, the human populations of all of the environments examined are considered to be at potential risk of mosquito-borne diseases.

Relative abundance and molecular identification of Culex pipiens complex (Diptera: Culicidae), in Kura Local Government Area, North-western Nigeria

Culex species are the most widespread mosquito species across the world and are known to be highly opportunistic, feeding on humans and livestock. They are known to acquire the potential to transmit zoonotic diseases, including Rift Valley Fever (RVF). However, despite their public health significance, they remain understudied in North-western Nigeria, compared to Anophelines. This study was therefore aimed at determining the relative abundance and Multiplex polymerase chain reaction (Multiplex PCR) identification of members of the Culex pipiens complex, in Kura Local Government Area (LGA), North-western, Nigeria. Adult mosquitoes were collected using Center for Disease Control (CDC) miniature light traps from August to October 2019. Mosquitoes were identified using morphological identification keys. Members of the Culex pipiens complex were further identified using Multiplex PCR to assess the presence of sibling species. A total of 413 mosquitoes, belonging to 3 genera, Culex, Anopheles and Aedes were collected. Of this figure, 120 Culex spp. females were collected. Homes with livestock had the highest occurrence of mosquitoes, 123 (61.19%) compared to those without livestock, 78 (38.81%). There was no statistical difference among the two (2) categories of homes (P ≥ 0.005). Culicoides spp. were the most common with 130 collected (65.38%). Again, homes with livestock had the highest occurrence, 85 whilst homes without livestock had 45 of the other flies caught. Multiplex- PCR revealed no expected bands for Cx. quinquefasciatus and Cx. pipiens from the DNA obtained from field collected mosquitoes as confirmed by using genomic DNA of an insectary Culex quinquefasciatus as control. Cx. spp. is presently regarded as a biting nuisance having no significant epidemiological importance. Efforts at its control should be intensified before it is too late. This study provides useful information on the occurrence and multiplex PCR of Culex spp in Kura Local Government Area, North-western Nigeria. These results have implications for the control of Culex spp. mosquito populations and the spread of human, livestock and avian diseases.

Distribution pattern and prevalence of West Nile virus infection in Nigeria from 1950 to 2020: a systematic review

OBJECTIVES

West Nile virus (WNV) is a re-emerging mosquito-borne viral infection. This study investigated the pooled prevalence pattern and risk factors of WNV infection among humans and animals in Nigeria.

METHODS

A systematic review was conducted of eligible studies published in PubMed, Scopus, Google Scholar, and Web of Science from January 1, 1950 to August 30, 2020. Peer-reviewed cross-sectional studies describing WNV infections in humans and animals were systematically reviewed. Heterogeneity was assessed using the Cochrane Q statistic.

RESULTS

Eighteen out of 432 available search output were eligible and included for this study. Of which 13 and 5 were WNV studies on humans and animals, respectively. Although 61.5% of the human studies had a low risk of bias, they all had high heterogeneity. The South West geopolitical zone of Nigeria had the highest pooled prevalence of anti-WNV immunoglobulin M (IgM; 7.8% in humans). The pooled seroprevalence of anti-WNV IgM and immunoglobulin G (IgG) was 7.1% (95% confidence interval [CI], 5.9 to 8.3) and 76.5% (95% CI, 74.0 to 78.8), respectively. The WNV RNA prevalence was 1.9% (95% CI, 1.4 to 2.9), while 14.3% (95% CI, 12.9 to 15.8) had WNV-neutralizing antibodies. In animals, the pooled seroprevalence of anti-WNV IgM and IgG was 90.3% (95% CI, 84.3 to 94.6) and 3.5% (95% CI, 1.9 to 5.8), respectively, while 20.0% (95% CI, 12.9 to 21.4) had WNV-neutralizing antibodies. Age (odds ratio [OR], 3.73; 95% CI, 1.87 to 7.45; p<0.001) and level of education (no formal education: OR, 4.31; 95% CI, 1.08 to 17.2; p<0.05; primary: OR, 7.29; 95% CI, 1.80 to 29.6; p<0.01) were significant risk factors for WNV IgM seropositivity in humans.

CONCLUSIONS

The findings of this study highlight the endemicity of WNV in animals and humans in Nigeria and underscore the need for the One Health prevention and control approach.

Serosurvey of West Nile virus in household-reared pigeons in Bauchi metropolis, Nigeria

Background

In Nigeria not much is known about West Nile virus (WNV) in pigeons. This study determined the involvement of household-reared pigeons in the circulation of WNV in Nigeria.

Methods

It was a cross-sectional study. Serological detection was done using competitive enzyme-linked immunosorbent assay and a pretested interviewer-administered questionnaire was used to collect information on risk factors related to WNV in households.

Results

From the156 households enumerated, 376 pigeon serum samples were collected and tested for antibodies. A total of 3.5% (13/376) of the pigeon sera were positive. Risk factors for WNV in households indicated that not having a blocked or stagnant gutter that is not flowing, and having mosquito nets at the windows and doors were found to be protective (OR=0.69, 95% CI, 0.21-2.29; OR=0.46, 95% CI, 0.14-1.56).

Conclusions

Household-reared pigeons contribute to the epidemiology of WNV. There is need for further studies in other species of birds, and education of the populace about its zoonotic transmission.

Emergence and Associated Risk Factors of Vector Borne West Nile Virus Infection in Ilorin, Nigeria

BACKGROUND

West Nile Virus (WNV) is a mosquito-borne viral pathogen that is the causative agent of West Nile fever and encephalitis. Diagnostic tools for WNV infection in Nigeria are not well established hence the current prevalence rate of WNV infection in Nigeria is unknown. We aimed to establish the serological prevalence of WNV infection in febrile patients in Ilorin, Nigeria in 2016, and to assess the risk factors associated with the acquisition of the virus.

METHODS

This was a cross-sectional study involving the screening of subjects presenting with febrile illnesses. While specific IgM ELISA was used to determine the seroprevalence, a closed-ended questionnaire was used to ascertain the risk factors associated with this viral infection.

RESULTS

Fifteen (7.5%) of the respondents were positive for WNV infection. Subjects living in areas in close proximity to trees and bushes (P= 0.011) and stagnant water (P= 0.001) were at a higher risk of having WNV infection. Other risk factors associated with WNV among the respondents include the none use of insecticide (P= 0.001), sitting out at night (P= 0.044), HIV positivity (P= 0.003) and having an organ transplant (P= 0.002).

CONCLUSION

This study clearly shows a considerable WNV infection in Ilorin, with the presence of factors that can promulgate an outbreak, hence a need for further surveillance in the study area.

Comparative Vector Competence of North American Culex pipiens and Culex quinquefasciatus for African and European Lineage 2 West Nile Viruses

West Nile virus (WNV) is a mosquito-borne flavivirus that is phylogenetically separated into distinct lineages. Lineage 1 (L1) and lineage 2 (L2) encompass all WNV isolates associated with human and veterinary disease cases. Although L1 WNV is globally distributed, including North America, L2 WNV only recently emerged out of sub-Saharan Africa into Europe and Russia. The spread of L2 WNV throughout and beyond Europe depends, in part, on availability of competent vectors. The vector competence of mosquitoes within the Culex genus for WNV is well established for L1 WNV but less extensively studied for L2 WNV. Assessing the vector competence of North American Culex mosquitoes for L2 WNV will be critical for predicting the potential for L2 WNV emergence in North America. We address the vector competence of North American Culex pipiens and Culex quinquefasciatus for L2 WNV. Both mosquito species were highly competent for each of the L2 WNV strains assessed, but variation in infection, dissemination, and transmission was observed. An L2 WNV strain (NS10) isolated during the Greek outbreak in 2010 exhibited a reduced capacity to infect Cx. pipiens compared with other L2 WNV strains. In addition, a South African L2 WNV strain (SA89) displayed a significantly shorter extrinsic incubation period in Cx. quinquefasciatus compared with other L2 WNV strains. These results demonstrate that North American Culex mosquito species are competent vectors of African and European L2 WNV and that emergence of L2 WNV is unlikely to be hindered by poor competence of North American vectors.

Evidence of exposure of laughing doves (Spilopelia senegalensis) to West Nile and Usutu viruses in southern Tunisian oases

It has previously been suggested that southern Tunisian oases may be suitable areas for the circulation of flaviviruses. In order to anticipate and prevent possible epidemiological spread of flaviviruses in humans and domestic animals, the ecology of their transmission in the oasis system needs to be better understood. Thus, the aim of this study was to assess the seroprevalence of anti-flavivirus antibodies in the laughing dove (Spilopelia senegalensis), an abundant resident bird in Tunisian oases. Anti-flavivirus antibodies were detected in 17% of sampled doves. Ten per cent of the total tested doves were West Nile virus (WNV) seropositive and 4% were Usutu virus (USUV) seropositive, which provides the first evidence of USUV circulation in Tunisian birds. We also found that the occurrence probability of anti-flavivirus antibodies in dove plasma increased with decreasing distance to coast, suggesting that doves inhabiting coastal oases were more exposed to flaviviruses compared with those inhabiting inland oases. We also found significantly higher antibody occurrence probability in adult doves compared with young doves, which underlines the effect of exposure time. Overall, our results suggest that the laughing dove may be used for WNV and USUV surveillance in southern Tunisia. They also stress the need for investigations combining data on birds and mosquitoes to better understand the ecological factors governing the circulation of flaviviruses in this area.

Population dynamics of mosquito species in a West Nile virus endemic area in Madagascar

Human and animal serological surveys suggest that West Nile virus (WNV) circulation is widely distributed in Madagascar. However, there are no reported West Nile fever outbreaks or epizootics in the country and only one fatal human case has been reported to date. Currently there is very limited information on the maintenance and the transmission of WNV in Madagascar and particularly on the mosquito species involved in transmission cycles. In 2014, we initiated a study to investigate mosquito species composition, relative abundance, and trophic behavior in Mitsinjo District close to Lake Kinkony, a WNV endemic area in north-western Madagascar. We collected a total of 2519 adult mosquitoes belonging to 21 different species. The most abundant species was Aedeomyia (Aedeomyia) madagascarica Brunhes, Boussès & da Cunha Ramos, which made up 83% of all the mosquitoes collected. Mosquito abundance was associated with proximity to the lake (Morafeno and Ankelimitondrotra). Additionally, a correlation was observed between the lake-side biotope and the abundance of mosquito vectors in Morafeno. WNV RNA was detected in one pool of Ae. madagascarica and one pool of Anopheles (Cellia) pauliani Grjebine, suggesting that these two species may be involved in the maintenance and/or transmission of WNV in Madagascar.