Multiple causes of variable tick burdens on small-mammal hosts

Area of Science:

• Ecology and Evolutionary Biology
• Epidemiology
• Parasitology

Background:

• Blacklegged ticks (Ixodes scapularis) transmit zoonotic diseases like Lyme disease.
• Understanding tick burdens on hosts is crucial for disease transmission control.
• Previous studies overlooked seasonal dynamics and tick aggregation on hosts.

Purpose of the Study:

• To develop a statistical model predicting tick burdens on individual hosts throughout the year.
• To identify factors influencing tick burdens on white-footed mice and eastern chipmunks.
• To explore host attributes contributing to disproportionate tick feeding.

Main Methods:

• Developed a statistical modeling framework incorporating temporal, site, and individual attributes.
• Utilized a negative binomial distribution to account for tick aggregation.
• Analyzed an 11-year dataset of Ixodes scapularis burdens on mice and chipmunks.

Main Results:

• Tick burdens increased with host-seeking tick densities, indicating host saturation.
• Host switching dynamics observed: chipmunks draw larvae from mice, mice draw nymphs from chipmunks.
• Strong tick aggregation on hosts suggests undiscovered individual host qualities are responsible.

Conclusions:

• Tick burdens are complex, influenced by seasonality, host density, and host switching.
• No single individual correlate (sex, age, mass) explained disproportionate tick burdens.
• Hosts feeding more nymphs also tend to feed and infect more larvae, but predicting these hosts remains challenging.