Can ticks pass Heartland virus to their offspring and to other ticks feeding nearby?

Details

Heartland virus (HRTV; Bunyaviridae: Phlebovirus) was described as a recently identified cause of human illness in the United States. After field studies conducted in 2012 implicated Amblyomma americanum (L.) as a vector, researchers conducted laboratory experiments to assess this tick species’ ability to transmit HRTV.

Larval and nymphal ticks were immersed in high-titer HRTV suspensions and tested for virus at various intervals afterward. In a later trial, larvae were immersed in HRTV and then allowed to feed to engorgement on a rabbit. After they molted, a subset of the resulting nymphs was tested for HRTV to document transstadial transmission—persistence of the virus across a molt. Presumed infected nymphs were also allowed to feed alongside uninfected laboratory-colony larvae to assess nonviremic transmission.

In another trial, nymphs fed on a rabbit and were allowed to molt into adults. Male and female ticks then fed and mated on a rabbit, and females were allowed to lay eggs. Researchers tested males and females that had finished laying eggs for HRTV, and tested the offspring of infected females to assess vertical transmission from mother to offspring.

Infection rates were ≤50% in immersed larvae and nymphs tested at intervals after immersion. Transmission across developmental stages was documented from larvae to nymphs and then to adults. HRTV was detected in a pooled sample of nymphs that had molted from initially uninfected larvae fed alongside infected nymphs. Vertical transmission was observed in the offspring of infected females. Infected females took longer to lay eggs and produced fewer offspring.

Rabbits fed upon by immersed larvae or ticks infected across developmental stages showed seroconversion—an antibody response—without viremia, indicating horizontal transmission of HRTV.