Background
Lyme disease (LD) is a common vector-borne disease in North America. Understanding the causes behind inter-annual fluctuations of LD incidence can help warn healthcare providers of upcoming outbreaks.
Objective
Identifying what specific climate variables affects the vector, Ixodes scapularis ticks, and ultimately LD incidence.
Methods
A systematic review was carried out to understand how climate variables affect the tick population variables that are related to LD.
Results
Twenty-one studies met the inclusion criteria. Risk of bias was generally rated “low” or “probably low” and quality of evidence was rated “moderate”. Strength of evidence was assessed for tick abundance, a proxy for LD. The relationship with climatic moisture was rated as “sufficient”, but was rated “inadequate” for temperature and temperature+moisture. A positive, moderate-strong relationship between prior climatic moisture and tick abundance (r=0.82; r2=0.56–0.64) was observed in 50% of studies. The relationship was observed in 75% of nymph-only abundance studies. While relationships were observed between tick abundance and temperature (70% of studies, r=(-0.89)–0.93; r2=(-0.56)–0.34) and temperature+moisture (38% of studies, 75% negative relationships), direction and magnitude could not be determined.
Conclusion
Higher climatic moisture (yearly or 0.5–2 years prior) increases tick abundance and, by proxy, LD incidence. Nymph-only abundance studies, a more accurate proxy, was more likely to show this relationship. Climate change is predicted to increase precipitation in Northeast US/Canada, which appears likely to increase LD incidence
