About

Dr. Guiyun Yan is a Chancellor’s Professor in the Department of Population Health & Disease Prevention at the University of California, Irvine, with a focus on global health. He earned his Ph.D. in Biology from the University of Vermont in 1994. Dr. Yan's research centers on the epidemiology of vector-borne diseases and vector biology. His work includes evaluating the effects of environmental modifications and invasive vectors on malaria transmission and disease burden in Africa, assessing the impact of urbanization on dengue transmission and vector ecology in Asia, studying the ecological genetics of insecticide resistance, and developing adaptive and locally tailored vector intervention strategies. Dr. Yan also serves as the program director for a Center of Excellence for Malaria Research (ICEMR) in Ethiopia and Kenya, funded by the National Institutes of Health (NIH), and is the project director for a global infectious disease training program funded by the Fogarty International Center.

Research topics

• Biology
• Ecology
• Immunology
• Veterinary medicine
• Medicine
• Genetics
• Toxicology
• Environmental health
• Zoology

Selected publications

• Reduced bio-efficacy of aged PermaNet® 3.0 Nets against local pyrethroid-resistant Anopheles arabiensis in Western Kenya

  Frontiers in Tropical Diseases · 2026-01-30 · 1 citations

  articleOpen accessSenior authorCorresponding

  Background Long-lasting insecticidal nets (LLINs) are central to malaria control and designed to protect for up to three years; however, increasing pyrethroid resistance undermines their effectiveness. Piperonyl butoxide (PBO) LLINs, designed to enhance pyrethroid efficacy, are recommended in high-resistance areas, yet their long-term operational bio-efficacy remains unclear. This study evaluated the killing efficacy of PBO LLINs over three years of field use compared to standard LLINs and monitored insecticide resistance in local Anopheles gambiae s.l. populations. Methods During a trial in Muhoroni, western Kenya (2021–2024), standard and PBO LLINs were collected at 6, 18, and 36 months of use. Residual bio-efficacy was assessed using WHO cone bioassays against a susceptible Anopheles gambiae s.s. Kisumu strain and field An. gambiae s.l. populations. WHO tube and bottle assays determined insecticide resistance, while synergist assay assessed metabolic resistance. Quantitative polymerase chain reaction detected target-site mutations ( kdr -1014 F/S and Ace-1 G119S). Results Molecular identification confirmed all An. gambiae s.l. were Anopheles arabiensis , showing increasing pyrethroid resistance, with deltamethrin mortality declining from 96.3% (2021) to 22.7% (2024) while remaining susceptible to pirimiphos-methyl and clothianidin. PBO pre-exposure restored deltamethrin mortality from 22.7% to 98.9%. The frequency of 1014F increased from 0.09 to 0.17 and 1014S from 0.04 to 0.06, with no Ace-1 mutations detected. Standard LLINs retained >80% efficacy against the susceptible strain for 18 months but were below threshold against field mosquitoes even when new. PBO LLINs were effective at baseline against field populations but declined sharply, with mortality dropping to 24% by 6 months. Overall, both net types exhibited a marked decline in killing efficacy over time against field mosquitoes, with mortality falling < 20% within six months. Conclusion Anopheles arabiensis showed increasing pyrethroid resistance, driven largely by metabolic mechanisms. Standard LLINs showed suboptimal killing efficacy against field populations, while PBO LLINs achieved high baseline efficacy but declined significantly by six months. These findings indicate that PBO LLINs can improve protection against resistant vectors but may be insufficient in high-resistance areas, underscoring the need for alternative non-pyrethroid interventions, strategic deployment, and revised LLIN re-distribution cycles aligned with their functional lifespan.

  PublisherOA PDFDOI

• Supplemental data for "Effectiveness of an adaptive intervention strategy for malaria vector control: A cluster sequential multiple assignment randomized trial (SMART)"

  Open MIND · 2026-02-28

  datasetSenior author
  DOI

• Supplemental data for "Effectiveness of an adaptive intervention strategy for malaria vector control: A cluster sequential multiple assignment randomized trial (SMART)"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-02-28

  datasetOpen accessSenior author
  PublisherDOI

• Urban malaria in sub-Saharan Africa: a scoping review of epidemiologic studies

  Malaria Journal · 2025-04-19 · 13 citations

  reviewOpen access

  BACKGROUND: Malaria control in African cities faces challenges mainly due to unplanned urbanization and the spread of Anopheles stephensi. Urbanization is changing malaria dynamics, driven by environmental changes and population growth, with nearly 70% of people projected to live in urban areas by 2050. This scoping review maps the epidemiology of urban malaria in sub-Saharan Africa, identifying research gaps and guiding strategies for control and elimination. METHODS: A structured search across multiple databases was performed using predefined eligibility criteria to select articles. Accordingly, PubMed, Medline EBSCO, Google scholar, Science direct, Cochrane library and grey literature sources were searched for relevant articles. The Joanna Briggs Institute (JBI) guidelines were followed for evidence selection, data extraction, and presentation of findings. Peer-reviewed and gray literature published in English after 2014 that reported on the prevalence, incidence, or risk factors of urban malaria in sub-Saharan Africa was included in the review. RESULTS: Of the 2459 records identified from various databases, 32 articles were selected for review. A majority of those reviewed studies were community-based studies conducted in urban settings of sub-Saharan African countries. This review found the prevalence of malaria between 0.06% and 58%. This heterogeneity in prevalence is due to differences in diagnostic methods, study design, population characteristics, diagnostic methods, and environmental factors. A majority of those reviewed studies reported the prevalence between 10 and 30% with Plasmodium falciparum and Plasmodium vivax the dominant species. The review identified key factors associated with urban malaria infection, including socioeconomic status, travel history, prior infection, proximity to water sources, availability of vegetation in the compound, temperature, humidity, livestock ownership, and ITN utilization. CONCLUSION: This review found a high prevalence of urban malaria infection in sub-Saharan Africa and there was regional variation. Sociodemographic and socioeconomic status, travel history, ITN utilization, previous history of malaria infection and environmental factors like proximity to water sources, presence of vegetation, temperature, humidity, and livestock ownership were identified as factors associated with urban malaria infection. Hence, there is a need for a comprehensive approach to control urban malaria, including environmental management, improved diagnostics and treatment, socio-economic interventions, and better urban planning.

  PublisherOA PDFDOI

• Elevated Plasmodium Sporozoite Infection Rates in Primary and Secondary Malaria Vectors in Anopheles stephensi-Infested Areas of Ethiopia

  Insects · 2025-04-27 · 2 citations

  articleOpen accessSenior author

  Assessing bloodmeal sources and sporozoite infection rates in mosquito vectors is essential for understanding their role in malaria transmission. This study investigated these factors in Hawassa, Southern Ethiopia—an area recently invaded by Anopheles stephensi—through adult mosquito collections conducted between January and April 2023 using BG-Pro traps, CDC Light Traps, and Prokopack Aspirators. A total of 738 female Anopheles mosquitoes were collected, including An. arabiensis (72.9%), An. pharoensis (13.4%), An. stephensi (7.5%), and An. coustani (6.2%). Human Blood Index (HBI) values were 23.3% for An. arabiensis, 43.8% for An. pharoensis, 8.3% for An. stephensi, and 25.0% for An. coustani. Plasmodium infection was detected in 8% of An. arabiensis and 4.7% of An. pharoensis, while An. stephensi and An. coustani were uninfected. The findings highlight the presence of multiple competent malaria vectors, with significant infection rates observed in both primary and secondary species, underscoring the need to include secondary vectors in control and surveillance programs. The detection of An. stephensi alongside native vectors adds complexity to malaria control efforts, reinforcing the importance of continuous monitoring to understand the changing dynamics of vector populations and their roles in transmission.

  PublisherOA PDFDOI

• Effectiveness of an Adaptive Intervention Strategy for Malaria Vector Control: A Cluster Sequential Multiple Assignment Randomized Trial (SMART)

  SSRN Electronic Journal · 2025-01-01

  preprintOpen accessSenior author
  PublisherDOI

• Susceptibility of the invasive malaria vector Anopheles stephensi in Ethiopia to novel chemical insecticides and insect growth regulator

  Scientific Reports · 2025-08-18 · 2 citations

  articleOpen access

  The presence of invasive Anopheles stephensi has been confirmed from field studies in several urban, peri-urban and rural areas of Ethiopia. Recent studies have shown that these mosquitoes are resistant to common public health insecticides, namely pyrethroids (deltamethrin, permethrin, and alpha-cypermethrin), Carbamates (bendiocarb and propoxur), and organophosphates (pirimiphos-methyl). This study aimed to assess the susceptibility of populations of An. stephensi from Ethiopia to novel chemical insecticides recently recommended for vector control, namely, broflanilide (a meta-diamide targeting GABA receptors), clothianidin (a neonicotinoid disrupting nerve signals), and chlorfenapyr (a pyrrole disrupting respiratory pathways ), as well as pyriproxyfen (an insect growth regulator mimicking an insect juvenile hormone which results in adult mosquito emergence inhibition), which is recommended for mosquito larval control. The WHO bottle bioassay test was conducted to assess the susceptibility level of populations of An. stephensi reared from larval collections exposed to recommended diagnostic doses of broflanilide, clothianidin, chlorfenapyr, and pyriproxyfen at 18 µg/bottle, 10 µg/bottle 100 µg/bottle, and 100 µg/bottle, respectively. The solvent used was either a mixture of Mero and acetone or acetone alone. Control bottles were treated with solvent only. Mortality was recorded 24 hours post- exposure for all the insecticides and continued to 72 hours post- exposure for chlorfenapyr and pyriproxyfen. The effect of pyriproxyfen on mosquito fecundity (oviposition) was also assessed over four days after 72 hours holding period.Mortality rates of An. stephensi 24 hrs post-exposure to broflanilide and clothianidin was 100% (100/100), while mortality rates at 24 and 48 hrs post-exposure to chlorfenapyr was 66% (66/100), and 100% (100/100), respectively indicating high susceptibility of populations of An stephensi to the three candidate chemical insecticides. Mortality rates of An. stephensi 24hr , 48hr and 72 hr post-exposure to pyriproxyfen was 0%, 11% (11/100), and 15% (15/100), respectively. There was no mosquito mortality in the controls. Moreover, oviposition inhibition rate in adult female of An. stephensi exposed to pyriproxyfen was 100% while oviposition rate in adult female of An.stephensi in the control was 100%.The study revealed that populations of An. stephensi from Ethiopia were fully susceptible to the three novel chemical insecticides (broflanilide, chlorfenapyr and clothianidin) and an insect growth regulator ( Pyriproxyfen) resulted in complete oviposition inhibition. These findings suggest that the tested candidate chemical insecticides and insect growth regulator (IGR) can be used for indoor residual spraying (IRS) and larviciding, respectively for the control of an invasive malaria vector An. stephensi in Ethiopia.

  PublisherOA PDFDOI

• Effect of low-dose primaquine treatment on Plasmodium vivax recurrence and transmission-blocking activity in southwest Ethiopia: a longitudinal cohort study

  Malaria Journal · 2025-04-17 · 5 citations

  articleOpen accessSenior author

  BACKGROUND: Existing malaria control strategies for Plasmodium vivax are challenging due to its dormant and relapsing liver stages, as well as the early onset of gametocytogenesis. Primaquine (PQ) effectively eliminates dormant stages and can kill gametocytes; however, it necessitates repeated dosing. In this study, the effectiveness of chloroquine (CQ) plus low-dose of PQ on recurrence and its transmission-blocking activity was evaluated. METHODS: Between September 2019 and July 2022, a prospective cohort study was conducted in the Jimma-Arjo and Dabo-Hanna districts of the Oromia region in Ethiopia. A total of 214 uncomplicated cases of P. vivax malaria were enrolled in the study. Participants were treated with either CQ alone (106) or CQ + PQ (108), based on whether their district was targeted for P. vivax elimination by the national malaria programme or not. After enrolment, participants were followed for clinical illness and parasitaemia on days 28, 42, and monthly for one year. To assess the effect of different treatment regimens on transmission-blocking activity, Anopheles arabiensis mosquitoes were used in direct membrane-feeding assays (DMFA) at baseline (pre-treatment) and on day 42 (post-treatment). Based on polymerase chain reaction (PCR) positivity, the time to the first recurrence was estimated using Kaplan-Meier survival analysis. Cox regression models were employed to assess risk factors for recurrence. RESULTS: Of 3,590 individuals screened for malaria, 323 tested positive for P. vivax, and 214 were enrolled. Of these, 98.6% (211/214) completed the day 28 follow-up, and 67.3% (144/214) completed the one-year follow-up. Between days 28 and 42, 24% (95% CI 15.8-32.2%) of those individuals receiving CQ alone were PCR positive, and 10.3% (95% CI 4.5-16.0%) in those receiving CQ plus PQ. This represented a 57.3% reduction P. vivax recurrence in the CQ + PQ treatment group compared to CQ alone (risk ratio = 0.427, 95% CI 0.222-0.824, p = 0.008). During the year of follow-up at least one recurrence occurred in 70% (95% CI 59.1-80.2%) of the CQ alone and 46% (95% CI 35.5-58.1%) in the CQ + PQ treatment group (p < 0.001). Treatment regimen, high baseline parasitaemia and presence of gametocytaemia were risk factors for P. vivax recurrence. Compared to baseline DMFA at day 42, individuals showed an inhibition intensity of 39.0% in the CQ alone versus 77.8% in the CQ + PQ treatment group (p = 0.016), while inhibition prevalence was 35.2% in the CQ alone and 70.1% in the CQ + PQ treatment group (p = 0.021). CONCLUSIONS: This study demonstrate that with limited supervision of CQ + PQ treatment significantly lowers the risk of P. vivax recurrence in health clinics of southwest Ethiopia compared to CQ alone. Adding PQ to CQ also reduced P. vivax transmission to mosquito vectors relative to CQ alone but did not result in a complete transmission-blocking effect by day 42 post-treatment. Therefore, improved health education on treatment adherence and bed net use could enhance the effectiveness of PQ plus CQ. Higher doses of PQ for a shorter duration may be necessary to enhance treatment adherence, reduce recurrence rates, and decrease the risk of transmission.

  PublisherOA PDFDOI

• Genetic variation in olfactory pathways associated with host-seeking behavior in natural populations of Anopheles minimus, a primary malaria vector in western Thailand

  Parasites & Vectors · 2025-09-24

  articleOpen accessSenior author

  BACKGROUND: ), host odor, and body heat acting as key attractants. Along the Thai-Myanmar border, Anopheles minimus (the Funestus Group), a primary malaria vector, exhibits a stronger preference for human hosts than species of the Maculatus Group. Elucidating the genetic basis of this feeding behavior is essential for improving malaria control strategies. METHODS: Wild Anopheles mosquitoes were collected in Tha Song Yang district, Tak province, Thailand, from July 2019 to November 2020, using cow-baited traps, human landing catches, and Center for Disease Control (CDC) light traps. Specimens were identified morphologically and confirmed by Sanger sequencing of the cytochrome c oxidase subunit 1 (cox1) gene. We then performed whole-genome sequencing on An. minimus females categorized by host-seeking behavior: cow-baited collection (COW), human landing indoor (HLI), and human landing outdoor (HLO) to investigate the genetic determinants of host preference. RESULTS: Anopheles minimus females accounted for 25% of total samples (504/1,997). Cox1 sequencing revealed 143 unique haplotypes among 287 specimens, forming two major phylogenetic lineages, A (181 sequences) and B (106 sequences), suggestive of potential cryptic diversity. Whole-genome sequencing of An. minimus Lineage A from COW, HLI, and HLO groups yielded 12,659,785 variants. After filtering, 68,975 non-synonymous single-nucleotide polymorphisms (nsSNPs) remained. Comparing allele frequencies across the three pooled groups (FDR-adjusted p-value < 0.001) yielded 2,629, 2,948, and 4,369 significant nsSNPs, respectively. Gene Ontology (GO) analysis of genes harboring these nsSNPs showed strong enrichment for olfaction-related terms. The top six nsSNPs with olfactory annotations from each group comparison were selected for validation; Sanger sequencing confirmed their association with host-seeking preference. The VectorBase gene IDs for these candidate nsSNPs are AMIN001807, AMIN001339, AMIN003886, AMIN000912, AMIN003926, AMIN011060, AMIN002342, and AMIN015480. CONCLUSIONS: The observed significant genomic variance in field-collected An. minimus females, categorized by collection methods (reflecting host-seeking behavior), proposes a genetic underpinning for these behavioral variations. Differential nsSNPs within olfactory pathway genes might be functionally linked to host-seeking in this important malaria vector.

  PublisherOA PDFDOI

• Regional variation in sulfadoxine-pyrimethamine resistance genotypes and haplotypes of Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase genes in Western Kenya

  Malaria Journal · 2025-10-01 · 3 citations

  articleOpen accessSenior author

  BACKGROUND: Surveillance of molecular markers associated with antimalarial resistance in Plasmodium falciparum is critical for tracking the emergence, evolution, and spread of resistant malaria parasites in the population for timely and effective interventions. As shifting use of sulfadoxine-pyrimethamine (SP) in Kenya constitutes a differential selection pressure, this study compared resistance genotypes and haplotypes in P. falciparum isolates from endemic and epidemic regions of western Kenya. METHODS: A cross-sectional design was employed to collect blood samples from febrile patients residing in Ahero in Kisumu County, an endemic region, and Marani in Kisii County, an epidemic region. Molecular markers for antifolate resistance, dihydrofolate reductase (Pfdhfr) and dihydrofolate synthetase (Pfdhps), were genotyped for selected samples (N = 112) from Kisumu (n = 60) and Kisii (n = 52). Subsequent analysis was conducted for sequence polymorphisms, mutation frequency and haplotype prevalence. RESULTS: Genotyping of SP resistance markers identified 436H (28.8%), 437G (99%), and 540E (97.1%) in Pfdhps and 51I (100%), 59R (97.3%), and 108N (100%) in Pfdhfr as mutations that presented high frequency, with low multiplicity of infection (MOI) in both Kisumu (0.3196) and Kisii (0.2738). The double mutant SGEAA (70.18% in Kisumu vs. 51.06% in Kisii) and triple mutant HGEAA (26.31% vs. 44.68%) in Pfdhps, along with the triple mutant IRNI (86.67% vs. 98.08%) in Pfdhfr, exhibited significant regional differences in prevalence (p < 0.05). The Pfdhps-Pfdhfr haplotype analysis revealed a high prevalence of the quintuple mutant SGEAA-IRNI (57.89% in Kisumu vs. 48.94% in Kisii; p > 0.05) and a significantly higher prevalence of the sextuple mutant HGEAA-IRNI in Kisii compared to Kisumu (44.68% vs. 16.31%; p < 0.05). Comparatively, given that Pfdhps-516F and Pfdhfr-164L were the dominant alleles in Kisumu, while the Pfdhps-436H allele was dominant in Kisii, along with HGEAA and HGEAA-IRNI haplotypes (p < 0.05), they highlight regional variation in SP resistance genotypes and haplotypes. CONCLUSIONS: This study demonstrates that the fully resistant double Pfdhps-SGEAA and triple Pfdhfr-IRNI haplotypes have approached fixation in both endemic and epidemic regions, while the dominance of the 164L allele in the endemic region signals the emergence of super-resistance. These findings suggest a review of the therapeutic efficacy of SP and continuous surveillance of resistance due to the presence of fully resistant haplotype (SGEAA-IRNI) and super-resistant haplotype (F/HGEAA-IRNL) in the population of P. falciparum strains in western Kenya.

  PublisherOA PDFDOI

Recent grants

• NIH Grant R03TW007360

  NIH · $118k · 2009

• NIH Grant R56AI050243

  NIH · $508k · 2008

• A Novel Hydrology-based Malaria Transmission Model and Field Applications

  NIH · $418k · 2022–2025

• NIH Grant R03TW008237

  NIH · $183k · 2013

• NIH Grant R25TW008125

  NIH · $270k · 2012

Frequent coauthors

• Guofa Zhou

  University of California, Irvine

  136 shared

• Andrew K. Githeko

  135 shared

• Ming‐Chieh Lee

  University of California, Irvine

  116 shared

• Daibin Zhong

  University of California, Irvine

  95 shared

• James W. Kazura

  Case Western Reserve University

  64 shared

• Harrysone Atieli

  Maseno University

  63 shared

• Delenasaw Yewhalaw

  Jimma University

  56 shared

• Xiaoming Wang

  54 shared

Labs

• Yan LabPI

  Ecology of African malaria vectors; Malaria epidemiology; Dengue vector biology in Asia

Education

• Ph.D., Environmental Health Sciences

  University of California, Los Angeles

  2003

• M.S., Environmental Health Sciences

  University of California, Los Angeles

  1999

• B.S., Environmental Health Sciences

  University of California, Los Angeles

  1997

Awards & honors

• ICEMR Award of Excellence, NIAID, NIH, 2011
• Chancellor’s Fellow, UC Irvine, 2019