Diseases Spread by the Asian Longhorned Tick
The Asian longhorned tick (Haemaphysalis longicornis) primarily spreads Theileria orientalis, particularly the pathogenic Ikeda genotype, which causes theileriosis in cattle. This invasive tick species, recently established in the United States, poses significant risks to livestock health 1.
Primary Pathogens Transmitted
Confirmed Transmissions
- Theileria orientalis:
- The most well-documented pathogen transmitted by H. longicornis in the United States
- The Ikeda genotype was found in 12.7% of tested H. longicornis ticks in Virginia 1
- The Chitose genotype has also been detected in cattle in Missouri 2
- Causes Theileria-associated bovine anemia (TABA) in cattle, which can be mistaken for bovine anaplasmosis 2
Potential Transmissions Based on Native Range
In its native range in Asia and introduced areas like Australia and New Zealand, H. longicornis is known to transmit:
- Rickettsioses: Including spotted fever group rickettsiae 3
- Babesiosis: Causes bovine babesiosis (Babesia ovata) and canine babesiosis (Babesia gibsoni) 4
- Viral diseases: Various viral pathogens affecting humans and animals 4
Geographic Distribution and Spread
The Asian longhorned tick has rapidly expanded across the United States since its first detection in 2017:
- Initially found in New Jersey
- Now established in multiple eastern states including Virginia, Missouri, and New York 1, 2, 5, 6
- Most recently documented in Greene County, Missouri in 2021 6
Host Preferences
H. longicornis shows specific host preferences in the United States:
- Medium and large mammals: Particularly raccoons (55.4%), Virginia opossums (28.9%), and white-tailed deer (11.5%) 5
- Cattle: Frequently found on beef cattle in areas where the tick is established 2
- Low association with small mammals and birds: Unlike some native tick species 5
Unique Characteristics
- Reproductive capabilities: Exists in both bisexual (diploid) and parthenogenetic (triploid) forms, with the parthenogenetic form able to reproduce without mating 4
- Heavy infestations: Can reach extremely high numbers on individual hosts 4
- Environmental adaptability: Successfully established in various regions of the United States with different climates 6
Public Health Implications
While H. longicornis has been tested for numerous human pathogens in the United States (including Borrelia burgdorferi, Anaplasma phagocytophilum, and Bartonella spp.), current evidence suggests a relatively low potential for this tick to acquire and transmit human pathogens from wildlife hosts in its new range 5. However, vigilance is warranted as the tick continues to expand its territory and potentially adapt to new hosts and pathogens.
Clinical Relevance
For healthcare providers, it's important to:
- Consider theileriosis in differential diagnoses for cattle with anemia in areas where H. longicornis is established
- Be aware that TABA can be mistaken for bovine anaplasmosis, potentially delaying proper diagnosis and treatment 2
- Monitor for potential emergence of new tick-borne diseases as this invasive species continues to expand its range
The continued surveillance of this invasive tick species and the pathogens it may transmit remains crucial for protecting both animal and potentially human health in affected regions.