Malaria morbidity
Over the last nine years, 128,946 malaria cases were reported in the study area. Plasmodium falciparum and P. vivax were prevalent in the area and nearly had identical proportions with 66,570 (51.6%) and 62,376 (48.4%), respectively. According to the data, malaria transmission was dropping for three years in a row, from 2014 to 2016. However, from 2017 to 2019, there was slight increment. Then, after a drop in year 2020, number of malaria cases skyrocketed in 2022 (Fig. 2).
Larval habitat distribution, positivity, and Anopheles species composition
Anopheles stephensi larvae were detected in 28 (16.6%) of the 169 mosquito breeding sites surveyed. The frequent habitats where An. stephensi was discovered were water tanks, including plastic and metal, concrete water cisterns at construction sites, and car wash facilities (Table 1). During the survey, 2,012 Anopheles larvae were collected and reared, and 548 (27.7%) adult females Anopheles were emerged. Morphologically, 234 (42.7%) of 558 were identified to be An. stephensi. Other Anopheles species identified included, Anopheles gambaie (s.l.) (n=167; 30.5%), An. Pharoensis (n=98; 17.9%), and An. counstani (n=49; 8.9%). Fig. 1 depicts the distribution of An. stephensi’s breeding habitats.
Table 1 Anopheles mosquito larval habitat positivity and species composition by habitat types, Hawassa, southern Ethiopia, 2023
Abbreviation: no, not observed; spp., species
Habitat types
|
Surveyed habitats
n (%)
|
Positive for any mosquito larvae
n (%)
|
Positive for Anopheles Larvae
n (%)
|
Positive for
An. stephensi
n (%)
|
Anopheles spp.
|
Water tanks
|
57 (31.5)
|
24 (42.1)
|
20 (35.1)
|
20 (35.1)
|
|
Concrete water cisterns at construction sites
|
44 (26.2)
|
20 (45.5)
|
11 (25.0)
|
6 (13.6)
|
- An. stephensi and An. gambiae (s.l.)
|
Concrete water collection box for carwash
|
10 (6.0)
|
3 (30.0)
|
2 (20.0)
|
2 (20.0)
|
|
Shoreline / lakeadge
|
9 (5.4)
|
8 (88.9)
|
7 (77.7)
|
no
|
- An. gambiae (s.l.), An. pharoensis, and An. coustani
|
Drainage ditch
|
8 (4.8)
|
4 (50.0)
|
2 (25.0)
|
no
|
|
Discarded buckets
|
7 (4.2)
|
3 (42.8)
|
2 (28.6)
|
no
|
|
Manmade pools
|
5(3.0)
|
no
|
|
no
|
|
Swamps/marshes
|
4 (2.4)
|
4 (100.0)
|
4 (100.0)
|
no
|
- An. gambiae (s.l.), An. pharoensis, and An. coustani
|
Discarded tires
|
4 (2.4)
|
2 (50.0)
|
no
|
no
|
|
Tire tracks/Road paddles
|
4 (2.4)
|
2 (50.0)
|
2 (50.0)
|
no
|
|
Excavated ground for road construction
|
3 (1.8)
|
3 (100.0)
|
3 (100.0)
|
no
|
|
Others
|
14 (8.3)
|
7 (50.0)
|
1 (7.1)
|
no
|
|
Adult collection’s Anopheles species composition
The adult survey captured 449 female Anopheles, 53 (12.0%) of them were An. stephensi. Anopheles stephensi was captured by the BG Pro Trap and the ProkoPack Aspirator. No An. stephensi was captured by the CDC light trap. Anopheles gambiae (s.l.), An. pharoensis, An. coustani, and An. demeilloni were other Anopheles species collected during the survey. Anopheles gambiae (s.l.) was the predominant species (53.7%) followed by An. pharoensis (23.3%) and An. coustani (11.5%) (Fig. 3).
Molecular identification of An. stephensi
Of the 50 morphologically identified An. stephensi specimens analyzed, ITS2 PCR results were obtained from all of them. We compared the morphological identification to the ITS2 PCR endpoint assay results. With the PCR endpoint assay, 48 (96%) specimens were confirmed as An. stephensi. Only two of the 50 (4.0%) morphologically identified An. stephensi were not confirmed with the PCR endpoint assay. Sanger sequencing was performed for 30 confirmed and 2 not confirmed specimens. Of the 30 An. stephensi, 11 were found to be cox1 haplotype 2 (GenBank accession OQ865406) and cytb haplotype 2 (GenBank accession OQ863377), while 19 were cox1 haplotype 3 (GenBank accession OQ865407) and cytb haplotype 1 (GenBank accession OQ863376). The two specimens not confirmed by ITS2 PCR were identified as An. arabiensis by cox1 sequencing.