Tick-to-host transmission differs between Borrelia afzelii strains

Area of Science:

• Microbiology
• Epidemiology
• Vector-borne diseases

Background:

• Multiple-strain infections are common in both hosts and vectors of vector-borne pathogens.
• Host infections influence pathogen strain acquisition by vectors.
• The impact of vector multiple-strain infections on pathogen transmission remains unclear.

Purpose of the Study:

• To investigate if multiple-strain infections in nymphal ticks affect nymph-to-host transmission (NHT) of Borrelia afzelii.
• To determine the relationship between spirochete load and NHT for different B. afzelii strains.

Main Methods:

• Infected donor mice with single or multiple Borrelia afzelii strains (Fin-Jyv-A3, NE4049).
• Fed larval ticks on infected mice, allowing them to molt into infected nymphs.
• Exposed naive mice to infected nymphs to assess NHT and spirochete loads.

Main Results:

• Multiple-strain infections in mice reduced tick acquisition of both B. afzelii strains by 23%.
• Nymphs from multiple-strain infections were 46% less likely to transmit the focal strain to mice.
• Multiple-strain infection in nymphs did not alter NHT, but higher spirochete load (Fin-Jyv-A3) correlated with higher NHT.

Conclusions:

• Multiple-strain infections in the vectoring tick do not influence strain-specific transmission to new hosts.
• Pathogen abundance within the arthropod vector is a key factor in vector-to-host transmission.
• Understanding strain competition and pathogen load is crucial for predicting Lyme borreliosis epidemiology.