Spatiotemporal distribution and bionomics of Anopheles stephensi in different eco-epidemiological settings in Ethiopia

BACKGROUND

Malaria is a major public health concern in Ethiopia, and its incidence could worsen with the spread of the invasive mosquito species Anopheles stephensi in the country. This study aimed to provide updates on the distribution of An. stephensi and likely household exposure in Ethiopia.

METHODS

Entomological surveillance was performed in 26 urban settings in Ethiopia from 2021 to 2023. A kilometer-by-kilometer quadrant was established per town, and approximately 20 structures per quadrant were surveyed every 3 months. Additional extensive sampling was conducted in 50 randomly selected structures in four urban centers in 2022 and 2023 to assess households' exposure to An. stephensi. Prokopack aspirators and CDC light traps were used to collect adult mosquitoes, and standard dippers were used to collect immature stages. The collected mosquitoes were identified to species level by morphological keys and molecular methods. PCR assays were used to assess Plasmodium infection and mosquito blood meal source.

RESULTS

Catches of adult An. stephensi were generally low (mean: 0.15 per trap), with eight positive sites among the 26 surveyed. This mosquito species was reported for the first time in Assosa, western Ethiopia. Anopheles stephensi was the predominant species in four of the eight positive sites, accounting for 75-100% relative abundance of the adult Anopheles catches. Household-level exposure, defined as the percentage of households with a peridomestic presence of An. stephensi, ranged from 18% in Metehara to 30% in Danan. Anopheles arabiensis was the predominant species in 20 of the 26 sites, accounting for 42.9-100% of the Anopheles catches. Bovine blood index, ovine blood index and human blood index values were 69.2%, 32.3% and 24.6%, respectively, for An. stephensi, and 65.4%, 46.7% and 35.8%, respectively, for An. arabiensis. None of the 197 An. stephensi mosquitoes assayed tested positive for Plasmodium sporozoite, while of the 1434 An. arabiensis mosquitoes assayed, 62 were positive for Plasmodium (10 for P. falciparum and 52 for P. vivax).

CONCLUSIONS

This study shows that the geographical range of An. stephensi has expanded to western Ethiopia. Strongly zoophagic behavior coupled with low adult catches might explain the absence of Plasmodium infection. The level of household exposure to An. stephensi in this study varied across positive sites. Further research is needed to better understand the bionomics and contribution of An. stephensi to malaria transmission.

Dynamics of asymptomatic Plasmodium falciparum and Plasmodium vivax infections and their infectiousness to mosquitoes in a low transmission setting of Ethiopia: a longitudinal observational study

OBJECTIVE

A 15-month longitudinal study was conducted to determine the duration and infectivity of asymptomatic qPCR-detected Plasmodium falciparum and Plasmodium vivax infections in Ethiopia.

METHOD

Total parasite and gametocyte kinetics were determined by molecular methods; infectivity to Anopheles arabiensis mosquitoes by repeated membrane feeding assays. Infectivity results were contrasted with passively recruited symptomatic malaria cases.

RESULTS

For P. falciparum and P. vivax infections detected at enrolment, median durations of infection were 37 days (95% confidence interval [CI], 15-93) and 60 days (95% CI, 18-213), respectively. P. falciparum and P. vivax parasite densities declined over the course of infections. From 47 feeding assays on 22 asymptomatic P. falciparum infections, 6.4% (3/47) were infectious and these infected 1.8% (29/1579) of mosquitoes. No transmission was observed in feeding assays on asymptomatic P. vivax mono-infections (0/56); one mixed-species infection was highly infectious. Among the symptomatic cases, 4.3% (2/47) of P. falciparum and 73.3% (53/86) of P. vivax patients were infectious to mosquitoes.

CONCLUSION

The majority of asymptomatic infections were of short duration and low parasite density. Only a minority of asymptomatic individuals were infectious to mosquitoes. This contrasts with earlier findings and is plausibly due to the low parasite densities in this population.

A Retrospective Analysis of Malaria Trends in Leka Dulecha Health Center over the Last Ten Years (2013-2022), Western Oromia, East Wollega Zone

Background

Malaria is a serious public health concern in the world, and it causes a major socioeconomic problem in Ethiopia. Malaria data trend analysis of health facilities is useful to understand the prevalence and incidence of malaria cases and implementing evidence-based malaria control strategies. Hence, the main objective of this study was to investigate the malaria trends over the last ten years (2013-2022) at Leka Dulecha Health Center, East Wollega Zone, Western Oromia. Methodology. A retrospective study was conducted at Leka Dulecha Health Center to determine the trends of malaria prevalence by considering the malaria registration laboratory logbook for the last ten years from 2013 to 2022. Hence, to do this, sociodemographic data, years, months, and malaria prevalence were collected using a predesigned data collection sheet recorded from perspective between years.

Results

In the last ten years, a total of 30,576.00 suspected malaria cases were examined at Leka Dulecha Health Center, and out of these, 7,413.00 (24.24%) confirmed malaria cases were reported. In this health center, malaria cases were reported among both sexes and all age categories, but male (3,951.00, 54%) and age groups ≥ 15 years (3,994, 54%) were the most affected. The highest peak of malaria cases was reported during the autumn season (September, October, and November) followed by the spring season (March, April, and May) in the years of 2013 and 2007. In this study, the prevalence of malaria species was identified as Plasmodium falciparum, Plasmodium vivax, and mixed cases, with 5,014 (68%), 1,123 (15%), and 1,848 (25%), while Plasmodium falciparum was reported as the highest recorded cases.

Conclusion

Males and above 15 years old were more affected than the others. The highest peak malaria prevalence appeared from September to December of 2017 and 2013 years. Therefore, proper planning, implementation, and monitor of malaria prevention and control activities should be strengthened at all levels.

Factors associated with stunting among children aged 6-59 months in Bensa District, Sidama Region, South Ethiopia: unmatched case-control study

Background

Stunting remains one of the most common malnutrition problems among children in Ethiopia. Identifying the risk factors of stunting assists health planners to prioritize prevention strategies, and is a fundamental step for intervention. Therefore, this study aimed to assess factors associated with stunting among children aged 6–59 months in Bensa district, Sidama Region, South Ethiopia, 2018.

Methods

A facility-based unmatched case-control study was conducted from January 10 to March 10, 2018, on a sample of 237(79 cases and 158 controls) children aged 6–59 months with their respective mothers/caretakers. Data were collected using a structured, face-to-face interviewer-administered questionnaire and standard physical measurements. The data were entered into EP INFO version 7 and WHO Anthro software and analyzed using SPSS version 20. The variables were entered into the multivariable model using the backward stepwise regression approach. Multivariable logistic regression analysis was used to identify factors associated with stunting. Adjusted odds ratio (AOR) with 95% confidence interval (95%CI) and p-value <0.05 was used to declare the significance.

Results

Sex distribution was almost equal (Males = 52.3%, Females = 47.7%).The mean (standard deviation) age of cases and controls was 27.35 (±12.71) and 28.70 (±13.27) months respectively.

The risk factors for stunting were diarrhea in the past two weeks (AOR = 2.71, 95% CI: 1.42–5.16), being male (AOR = 2.37, 95% CI: 1.224–4.59), inappropriate exclusive breastfeeding (AOR =2.07, 95%CI: 1.07–4.01), having less than or equal to three under-five children in the household (AOR = 2.18, 95%CI: 1.03–4.64), and mothers who had no formal education (AOR =3.28, 95%CI :1.56–6.924).

Conclusions

Diarrhea in the past two weeks, sex of a child, inappropriate exclusive breastfeeding, number of under-five children in the household, and mothers who had no formal education were the risk factors of stunting. Thus organized efforts aimed at focus on prevention of diarrhea as part of an overall public health strategy for improving child health and nutrition. Educating mothers/caretakers on the importance of exclusive breastfeeding should be considered. Moreover, mothers need to be encouraged to space birth between children through the use of family planning services.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-021-03029-9.

Anopheles stephensi Mosquitoes as Vectors of Plasmodium vivax and falciparum, Horn of Africa, 2019

Anopheles stephensi mosquitoes, efficient vectors in parts of Asia and Africa, were found in 75.3% of water sources surveyed and contributed to 80.9% of wild-caught Anopheles mosquitoes in Awash Sebat Kilo, Ethiopia. High susceptibility of these mosquitoes to Plasmodium falciparum and vivax infection presents a challenge for malaria control in the Horn of Africa.

Comparison of infectivity of Plasmodium vivax to wild-caught and laboratory-adapted (colonized) Anopheles arabiensis mosquitoes in Ethiopia

BACKGROUND

Mosquito-feeding assays that assess transmission of Plasmodium from man-to-mosquito typically use laboratory mosquito colonies. The microbiome and genetic background of local mosquitoes may be different and influence Plasmodium transmission efficiency. In order to interpret transmission studies to the local epidemiology, it is therefore crucial to understand the relationship between infectivity in laboratory-adapted and local mosquitoes.

METHODS

We assessed infectivity of Plasmodium vivax-infected patients from Adama, Ethiopia, using laboratory-adapted (colony) and wild-caught (wild) mosquitoes raised from larval collections in paired feeding experiments. Feeding assays used 4-6 day-old female Anopheles arabiensis mosquitoes after starvation for 12 h (colony) and 18 h (wild). Oocyst development was assessed microscopically 7 days post-feeding. Wild mosquitoes were identified morphologically and confirmed by genotyping. Asexual parasites and gametocytes were quantified in donor blood by microscopy.

RESULTS

In 36 paired experiments (25 P. vivax infections and 11 co-infections with P. falciparum), feeding efficiency was higher in colony (median: 62.5%; interquartile range, IQR: 47.0-79.0%) compared to wild mosquitoes (median: 27.8%; IQR: 17.0-38.0%; Z = 5.02; P < 0.001). Plasmodium vivax from infectious individuals (51.6%, 16/31) infected a median of 55.0% (IQR: 6.7-85.7%; range: 5.5-96.7%; n = 14) of the colony and 52.7% (IQR: 20.0-80.0%; range: 3.2-95.0%; n = 14) of the wild mosquitoes. A strong association (ρ₍₁₆₎ = 0.819; P < 0.001) was observed between the proportion of infected wild and colony mosquitoes. A positive association was detected between microscopically detected gametocytes and the proportion of infected colony (ρ₍₃₁₎ = 0.452; P = 0.011) and wild (ρ₍₃₁₎ = 0.386; P = 0.032) mosquitoes.

CONCLUSIONS

Infectivity assessments with colony and wild mosquitoes yielded similar infection results. This finding supports the use of colony mosquitoes for assessments of the infectious reservoir for malaria in this setting whilst acknowledging the importance of mosquito factors influencing sporogonic development of Plasmodium parasites.