Haemaphysalis longicornis & Theileria orientalis Ikeda in the United States
Overview
The introduction and spread of the Asian longhorned ticks (Haemaphysalis longicornis) in the United States have raised significant concerns for animal health, given their role as a vector of Theileria orientalis genotype Ikeda, a protozoan parasite that causes severe disease in cattle. Since its first detection in the U.S. in 2017, this tick has expanded rapidly and is now established in multiple states, posing ongoing risks to livestock production.
The Vector: Haemaphysalis longicornis
Identification and Biology
Haemaphysalis longicornis is a small, reddish-brown hard tick native to East Asia. Key characteristics include (list). A unique feature of this species is its ability to reproduce parthenogenetically, meaning females can produce viable offspring without mating. This trait enables rapid population growth and high levels of infestation on hosts and in the environment.
Habitats and Hosts
Since its initial discovery, H. longicornis has been confirmed in numerous eastern and central U.S. states. It is commonly found in pastures and tall grasses, woodland edges, and livestock operations and wildlife habitats. The tick feeds on a wide range of hosts, including cattle, sheep, goats, horses, wildlife, companion animals, and humans.
The Pathogen: Theileria orientalis Ikeda
The Protozoan Parasite
Theileria orientalis is a tick-borne protozoan parasite that infects red blood cells in cattle. Among its genotypes, Ikeda is considered the most pathogenic and is responsible for significant clinical disease and production losses.
Disease in Cattle (Theileriosis)
Cattle infected with T. orientalis Ikeda may develop severe anemia, lethargy and weakness, jaundice, reduced weight gain and milk production, abortions, and death in severe cases. Adult cattle, particularly naïve animals with no prior exposure, are most severely affected. There is currently no approved treatment or commercial vaccine for T. orientalis Ikeda in the United States.
Transmission Cycle
- H. longicornis acquires T. orientalis Ikeda while feeding on infected cattle.
- The parasite is maintained in the tick and transmitted to new cattle during subsequent blood meals.
- Wildlife and other tick species are not currently known to play a major role in maintaining Ikeda in the U.S., making cattle–tick–cattle transmission the primary concern.
Economic and Agricultural Impact
The emergence of T. orientalis Ikeda threatens beef and dairy cattle health, farm profitability due to production losses, animal welfare, and increased costs for tick control and surveillance. Outbreaks have resulted in substantial economic losses for affected producers, particularly in regions where the tick is newly established.
Surveillance and Diagnosis
Diagnosis of T. orientalis Ikeda typically involves blood smear evaluation (limited sensitivity) followed by PCR testing to confirm infection and identify the Ikeda genotype. State and federal agencies, veterinary diagnostic laboratories, and universities play a critical role in monitoring tick distribution and disease occurrence.
Prevention and Control
Tick Management
Effective control focuses on reducing tick exposure including regular inspection of cattle, strategic use of approved acaricides, pasture management (mowing, brush control), and excluding wildlife where feasible.
Biosecurity
Biosecurity measures are important to protect animals from this vector and vector-borne disease. Producers should quarantine and inspect new or returning cattle, clean and inspect equipment and vehicles that move between farms, and report unusual illness or tick infestations to veterinarians or state animal health officials.
Public Health Considerations
While H. longicornis can bite humans, Theileria orientalis Ikeda does not infect people. However, the tick may carry other pathogens, and precautions should be taken to avoid tick bites when working outdoors.
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Additional Resources
For more information, contact:
- Your state department of agricuture
- Extension services
- Veterinary diagnostic laboratories
- USDA Animal and Plant Health Inspection Service (APHIS)
- Link to StoryMap(s) here!