Biology subjects

Tadesse, F. G.

Publications and source records attributed to Tadesse, F. G..

3 recordsLinked to original sources

bioRxiv2026

A joint Bayesian framework for modeling Plasmodium vivax transmission

Plasmodium vivax transmission from humans to mosquitoes depends on the density of gametocytes that in turn depends on asexual parasite replication and gametocyte commitment. These processes are often analyzed separately, despite being biologically linked and measured with substantial uncertainty. We used a joint Bayesian latent-variable model to simultaneously analyze parasite density, gametocyte density, and mosquito infectivity while accounting for measurement error and propagating uncertainty across linked processes. The model was applied to individual-level data from three P. vivax transmission studies conducted in Ethiopia (n = 455). A tenfold increase in gametocyte density was associated with more than a twofold increase in the odds of mosquito infection (odds ratio [OR] = 2.32, 95% credible interval [CrI]: 2.12-2.54). Asexual parasite density was also positively associated with infectivity after accounting for gametocyte density (OR = 1.74, 95% CrI: 1.60-1.90), and inclusion of parasite density improved predictive performance. Pathway decomposition within the joint model indicated that approximately 41% of the parasite-infectivity association operated through gametocyte density. Increasing age was associated with lower asexual parasite density but higher gametocyte density, resulting in minimal overall association with infectivity. Predicted infection probability increased sigmoidally with gametocyte density, remaining low at lower densities before increasing sharply and approaching a plateau at higher densities. Gametocyte density produced the largest predicted changes in the proportion of infected mosquitoes, while asexual parasite density added predictive information not fully captured by measured gametocyte density alone. This approach links molecular parasite measurements with mosquito infection risk while accounting for measurement uncertainty and provides an interpretable framework for studying the P. vivax infectious reservoir. Author SummaryMalaria transmission occurs when mosquitoes ingest sexual-stage parasites, called gametocytes, during a blood meal. In Plasmodium vivax infections, human-to-mosquito transmission depends on linked biological stages, including asexual parasite replication, gametocyte production, and mosquito infection. These processes are closely connected and often measured with uncertainty, making them difficult to study using standard approaches that analyze them separately. In this study, we applied a joint Bayesian model that analyzes parasite density, gametocyte density, and mosquito infectivity together while accounting for uncertainty in laboratory measurements. Using data from three studies in Ethiopia, we quantified how parasite density, gametocyte density, and host characteristics relate to mosquito infection. The analysis showed that measured gametocyte density alone did not fully explain variation in infectivity, and that asexual parasite density provided additional predictive information. We also found that age was associated differently with asexual parasite and gametocyte densities, resulting in little overall association with infectivity. This approach helps link molecular parasite measurements with transmission outcomes and improves understanding of the P. vivax infectious reservoir in endemic settings.

microbiology↗

bioRxiv2025

An evaluation of longitudinal Anopheles stephensi egg viability and resistance to desiccation over time

Anopheles stephensi, a malaria vector in South Asia and parts of the Middle East, has been detected as an invasive species in numerous African countries in recent years. It threatens to increase malaria disease burden and reverse gains made in malaria control and elimination over the past decades on the continent. To halt further expansion, it is critical to understand the biological characteristics that may have facilitated An. stephensi range expansion to Africa. In its invasive range, An. stephensi larvae have been found to colonize artificial containers, many of which are shared with Aedes aegypti. The success of Ae. aegypti as an invasive vector is often attributed to the use of artificial containers and the ability of Ae. aegypti eggs to remain viable in the absence of water for months. While An. stephensi is found in artificial containers, it is unclear whether the eggs can remain viable without water for extended periods. Anopheles stephensi eggs were reported to remain viable in soil for up to 12 days in a study done almost 100 years ago, but this work has not been revisited since. Thus, in this present study, we used egg batches (>100 eggs per batch) from two laboratory strains of An. stephensi (SDA500 and STE2) from South Asia and one Ae. aegypti strain (LVP-IB12) to evaluate 1) whether An. stephensi eggs can remain viable like Ae. aegypti when egg substrates are completely dried following standard insectary methods for drying out Aedes aegypti egg sheets, and 2) assess egg viability duration at varying temperatures (15{degrees}C, 20{degrees}C, 25{degrees}C 30{degrees}C, 35{degrees}C) when eggs are held on a moistened substrate in a high humidity environment. Anopheles stephensi egg viability and subsequent larval survival was observed consistently when moistened egg sheets were held at 15{degrees}C in a high humidity (>75% RH) environment for up to 14 days in both strains. Anopheles stephensi eggs were not viable when dried following standard insectary Aedes aegypti methods for drying out egg sheets, except when the protocol was amended to include a 15{degrees}C storage temperature. Though egg viability and larval survival was observed in the amended protocol for SDA500 and STE2 (16% and 21% respectively), it was significantly less than that of LVP-IB12 (83%) and was only observed in the egg batches stored for the shortest timepoint (seven days post egg collection, three days post complete drying of egg sheets). These findings suggest that An. stephensi may remain viable if eggs are transported under ideal conditions (15{degrees}C and >75% RH) through trade or commerce routes. Thus, the persistence of An. stephensi eggs in the absence of water should be considered in programs that engage in surveillance and control of An. stephensi in Africa.

ecology↗

bioRxiv2020

Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Anopheles stephensi, an efficient Asian malaria vector, recently spread into the Horn of Africa and may increase malaria receptivity in African urban areas. We assessed occurrence, genetic complexity, blood meal source and infection status of An. stephensi in Awash Sebat Kilo town, Ethiopia. We used membrane feeding assays to assess competence of local An. stephensi to P. vivax and P. falciparum isolates from clinical patients. 75.3% of the examined waterbodies were infested with An. stephensi developmental stages that were genetically closely related to isolates from Djibouti and Pakistan. Both P. vivax and P. falciparum were detected in wild-caught adult An. stephensi. Local An. stephensi was more receptive to P. vivax compared to a colony of An. arabiensis. We conclude that An. stephensi is an established vector in this part of Ethiopia, highly permissive for local P. vivax and P. falciparum isolates and presents an important new challenge for malaria control. Summary of the articleAn. stephensi, a metropolitan malaria vector that recently expanded to the Horn of African, was highly susceptible to local P. falciparum and P. vivax isolates from Ethiopia and may increase malariogenic potential of rapidly expanding urban settings in Africa.

microbiology↗