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Associations of Anaplasma phagocytophilum Bacteria Variants in Ixodes scapularis Ticks and Humans, New York, USA
Abstract:
Anaplasmosis, caused by the tickborne bacterium Anaplasma phagocytophilum, is an emerging public health threat in the United States. In the northeastern United States, the blacklegged tick (Ixodes scapularis) transmits the human pathogenic genetic variant of A. phagocytophilum (Ap-ha) and a nonpathogenic variant (Ap-V1). New York has recently experienced a rapid and geographically focused increase in cases of anaplasmosis. We analyzed A. phagocytophilum-infected I. scapularis ticks collected across New York during 2008-2020 to differentiate between variants and calculate an entomological risk index (ERI) for each. Ap-ha ERI varied between regions and increased in all regions during the final years of the study. Space-time scan analyses detected expanding clusters of Ap-ha located within documented anaplasmosis hotspots. Ap-ha ERI was more positively correlated with anaplasmosis incidence than non-genotyped A. phagocytophilum ERI. Our findings help elucidate the relationship between the spatial ecology of A. phagocytophilum variants and anaplasmosis.
Insights
Anaplasmosis risk is increasing in New York due to the pathogenic Anaplasma phagocytophilum variant (Ap-ha) carried by blacklegged ticks. Entomological risk increased across regions, with expanding Ap-ha clusters detected.
Area of Science:
- Veterinary Public Health
- Infectious Diseases
- Medical Entomology
Background:
- Anaplasmosis, a tickborne illness caused by Anaplasma phagocytophilum, is a growing public health concern in the US.
- The blacklegged tick (Ixodes scapularis) transmits both pathogenic (Ap-ha) and nonpathogenic (Ap-V1) A. phagocytophilum variants in the northeastern US.
- New York has observed a sharp, localized rise in anaplasmosis cases.
Purpose of the Study:
- To analyze the spatial distribution and prevalence of A. phagocytophilum variants in New York.
- To assess the entomological risk associated with pathogenic Ap-ha.
- To correlate tick variant distribution with human anaplasmosis incidence.
Main Methods:
- Analysis of A. phagocytophilum-infected I. scapularis ticks collected in New York from 2008-2020.
- Differentiation of pathogenic (Ap-ha) and nonpathogenic (Ap-V1) variants.
- Calculation of an entomological risk index (ERI) for Ap-ha.
- Space-time scan analyses to detect expanding clusters.
Main Results:
- Ap-ha ERI showed regional variation and increased statewide in recent years.
- Expanding clusters of Ap-ha were identified within known anaplasmosis hotspots.
- Ap-ha ERI demonstrated a stronger positive correlation with anaplasmosis incidence compared to non-genotyped ERI.
Conclusions:
- The spatial ecology of A. phagocytophilum variants is closely linked to anaplasmosis transmission.
- Entomological surveillance of tick variants can inform public health risk assessment.
- Findings highlight the increasing threat of pathogenic Anaplasma in New York.
