Authors: Poh Karen C, Oyen Kennan, Onzere Cynthia K, Kappmeyer Lowell S, Bastos Reginaldo G
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: *Haemaphysalis longicornis* and *Theileria haneyi* Transmission *Theileria haneyi*, a newly identified tick-borne hemoparasite causing equine piroplasmosis, has complicated diagnosis of this notifiable disease worldwide, particularly as *Haemaphysalis longicornis* ticks have recently become established in the United States. Researchers fed larvae and nymphs of *H. longicornis* on a splenectomized horse with acute *T. haneyi* infection (parasitemia ranging from 2.2–8.1% of circulating red blood cells), then monitored whether freshly moulted nymphs and adults could transmit the parasite to naïve horses over a 38-day observation period using nested PCR and blood smear analysis. Notably, whilst 100% of engorged larvae tested positive for *T. haneyi* DNA, the parasite failed to establish infection in any transmission horse exposed to moulted ticks—despite successful infection being confirmed when naïve horses received direct red blood cell inoculation from the source animal. These results indicate that *H. longicornis* cannot serve as a competent transstadial vector for *T. haneyi*, which has significant implications for risk assessments and surveillance strategies in regions where this tick species is expanding. However, practitioners should remain vigilant for other potential *Theileria* vectors and recognise that direct horse-to-horse transmission via blood contact or other tick species remains possible.
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Practical Takeaways
- •H. longicornis tick presence in the US does not represent an additional risk pathway for T. haneyi transmission through transstadial tick-borne spread, simplifying epidemiological risk assessment
- •Other tick vectors or direct transmission routes remain the primary concern for T. haneyi exposure and should be the focus of biosecurity and surveillance protocols
- •Clinical diagnosis of T. haneyi infection should not be attributed to H. longicornis parasitism alone; investigation of other potential vector species and transmission sources is warranted
Key Findings
- •Haemaphysalis longicornis larvae acquired T. haneyi (10/10 nPCR positive), but nymphs showed lower acquisition rate (4/10 nPCR positive)
- •No transstadial transmission occurred: freshly molted nymphs and adults (n=494) failed to transmit T. haneyi to naive horses despite tick feeding
- •Direct blood inoculation successfully transmitted T. haneyi with parasitemia detected at 15 days and clinical signs of acute infection
- •H. longicornis cannot serve as a competent vector for transstadial transmission of T. haneyi despite being an established tick species in North America