Dangerous hitchhikers
Tick-borne pathogen threats to U.S. cattle operations
By Joshua P Jackson, Lee Cohnstaedt and Cassandra Olds
Around the world, ticks pose a significant and increasing threat to both human and animal health. These eight-legged parasites are arachnids (in the same group as spiders and mites), with a life cycle that consists of four stages: egg, larvae, nymph and adult. All ticks are obligate blood feeders, meaning that they must bite and consume a blood meal from a vertebrate host in order to survive and progress through their life cycle. This recurrent need to blood feed coupled with the fact that many species of ticks can harbor a wide range of disease-causing viruses, bacteria, parasites and other pathogens, make them excellent vectors for pathogen transmission.
Each year, diseases caused by these tick-borne pathogens result in an estimated $13-19 billion in losses to livestock producers, including cattle producers, in the United States alone (Garcia et. al., 2022). Key economic consequences in cattle herds include the death of individual animals, loss of fertility, as well as reduced weight gain and milk production (Regitano, et. al., 2010). Major tick-borne threats to U.S. cattle producers include cattle tick fever (Bovine Babesiosis), Anaplasmosis and Theileriosis. Disease symptoms such as fever and anemia are very similar for all three pathogens, which can complicate diagnosis and treatment. Producers, veterinarians and other stakeholders should remain on alert for signs of tick infestation within their herds and consider early diagnostic testing at the first sign of a suspect illness in their cattle.
Cattle tick fever: Gone but not forgotten Despite a successful eradication campaign in the United States, the potential re-introduction of Bovine Babesiosis, more commonly known as “cattle tick fever,” remains a potent threat to the U.S. cattle industry. The disease occurs after infection with the protozoan parasite Babesia bigemina and Babesia bovis and is transmitted through the bite of infected Rhipicephalus (Boophilus) annulatus and Rhipicephalus (Boophilus) microplus ticks, collectively called cattle fever ticks. Symptoms of the disease in cattle include fever, anemia, anorexia and red colored urine. Infection with B. bovis may also result in the development of neurological symptoms such as vision and gait disturbances and coma.
Though both the pathogen and host ticks are no longer present within the U.S., babesiosis has historically been a major source of economic losses to cattle operations throughout the 19th and early 20th centuries and remains a significant challenge in many parts of the world. Currently, both species of cattle fever ticks are still found in Mexico, a key agricultural trading partner. Some estimates report that over half of the territories of Mexico contain populations of cattle fever ticks and that roughly 75% of cattle have experienced babesia infection (Teel, Hairgrove, 2024).
To prevent the re-introduction of babesiosis into the U.S., the USDA’s Animal and Plant Health Inspection Service oversees a permanent quarantine zone that has been established along the U.S.-Mexico border. In this zone, active surveillance measures and livestock inspections are conducted to look for the presence of cattle fever ticks, and eradication efforts are continually conducted to prevent the spread of these tick populations northward. All cattle leaving this zone must undergo treatments such as passing through dipping vats filled with acaricide chemicals and pass tick inspections before being cleared for shipment throughout the U.S.
Despite these measures many challenges remain, including stray livestock, an increase in the population of tick-carrying wildlife species in the border area, and a rise in acaricide-resistant tick populations throughout Mexico (Teel, Hairgrove, 2024; Esteve-Gasent, et. al., 2020). With the U.S. importing over 1 million head of cattle from Mexico each year, producers and other members of the cattle industry must remain vigilant to prevent the re-introduction of this tick and its associated devastating disease.
Anaplasmosis: Clear and present dangerIn cattle, Anaplasmosis caused by infection with the bacterium Anaplasma marginale is characterized by progressively worsening and sometimes fatal anemia. Bacteria replicate in the host’s red blood cells, eventually rupturing those cells to escape into the bloodstream and further spread the infection. Anaplasma marginale is one of the most common tick-borne pathogens in the world, present on six continents and capable of being transmitted by over 20 species of ticks (Teel, Hairgrove, 2024). In North America, this pathogen is predominantly transmitted by ticks of the Dermacentor genus, including the Rocky Mountain wood tick (Dermacentor andersoni) and the American dog tick (Dermacentor variabilis).
Infection in a cattle herd can result in severe losses to producers, including death and abortions in infected cattle, 20-30% reduction in weight gain, and an increase in the cull rate of up to 30% (Railey, Marsh, 2021). Cattle recovering from acute disease can remain persistently infected for the remainder of their lives, harboring low levels of bacteria and continuing to infect blood-feeding ticks that can then go on to infect other animals (Kocan et. al., 2010). In addition to vector transmission through tick bites, A. marginale bacteria can be transmitted mechanically through veterinary instruments such as needles and scalpels contaminated with infected blood, as well as through biting flies (Kocan et. al., 2010).
Looming threat on the horizon As the global agricultural system becomes increasingly interconnected, transboundary threats such as invasive species and foreign animal diseases play an increasingly pivotal role in agricultural security. The introduction of the Asian longhorned tick, Haemaphysalis longicornis, into the U.S. serves as a stark reminder of the dangers these types of threats can produce. Endemic to eastern Asia, H. longicornis was first confirmed in the U.S. in 2017 in New Jersey. It has since spread rapidly to at least 17 states and is continuing to expand (Poh, et. al., 2024). Unlike most tick species, the Asian longhorned tick can reproduce asexually through a process called parthenogenesis, in which the female ticks produce cloned copies of themselves. This has likely played a role in the tick’s ability to rapidly establish populations within the U.S., as a single female can produce thousands of offspring.
This tick species preferentially parasitizes cattle and is often found in extremely large numbers on bovine hosts. These infestations are sometimes large enough to cause severe blood loss in the animal. Besides the physical toll taken on cattle from heavy tick infestations, the Asian longhorned tick is a vector for the protozoal parasite Theileria orientalis, which can cause severe illness and even death in infected cattle. First reported on a farm in Virginia, T. orientalis infections have since been reported in several states with established populations of Asian longhorned ticks (Teel, Hairgrove, 2024). As the tick’s range continues to expand, producers should prepare for the incidence of T. orientalis infections to expand along with it. In addition, the mechanical transmission of T. orientalis through needles is possible. This, together with interstate animal movement, means that outbreaks may occur even in the absence of the tick vector.
Protecting the herdAt present, methods to control tick populations depend largely on the widespread use of chemical acaricides. Though initially effective, sustained use of these chemicals comes with a cost, including the rise of acaricide resistance among tick populations, as well as the risk of chemical residues remaining present in both livestock and the environment (Ghosh et. al., 2007). Despite these challenges, there are promising efforts underway to expand the tools available to livestock producers to combat ticks.
Advances in bioinformatics and sequencing technologies are beginning to expand our knowledge of tick and parasite genomes, providing information that can be used to target the development of vaccines against both. In addition, more sustainable and natural methods such as the controlled burning of pastures have been shown to reduce tick populations in the environment without the use of harmful chemicals (Polito et. al., 2013). By harnessing advancements in knowledge and technology, researchers and producers can continually work to develop and improve long-term, sustainable, and integrated strategies to manage the threat of tick-borne pathogens and protect their herds and livelihoods.
Sources:
Esteve-Gasent MD, Rodríguez-Vivas RI, Medina RF, Ellis D, Schwartz A, Cortés Garcia B, Hunt C, Tietjen M, Bonilla D, Thomas D, et al. Research on Integrated Management for Cattle Fever Ticks and Bovine Babesiosis in the United States and Mexico: Current Status and Opportunities for Binational Coordination. Pathogens. 2020; 9(11):871. https://doi.org/10.3390/pathogens9110871
Garcia, K.; Weakley, M.; Do, T.; Mir, S. Current and Future Molecular Diagnostics of Tick-Borne Diseases in Cattle. Vet. Sci. 2022, 9, 241. https://doi.org/10.3390/vetsci9050241
Ghosh, S. S. R. I. K. A. N. T. A., P. A. L. A. V. E. S. A. M. Azhahianambi, and M. P. Yadav. "Upcoming and future strategies of tick control: a review." Journal of vector borne diseases 44.2 (2007): 79.
Karen C. Poh, Mitzi Aguilar, Janaína Capelli-Peixoto, Sara K. Davis, Massaro W. Ueti, Haemaphysalis longicornis (Acari: Ixodidae) does not transmit Babesia bovis, a causative agent of cattle fever, Ticks and Tick-borne Diseases, Volume 15, Issue 6, 2024,102374, ISSN 1877-959X, https://doi.org/10.1016/j.ttbdis.2024.102374. (https://www.sciencedirect.com/science/article/pii/S1877959X24000670) Keywords: Asian longhorned tick; Haemaphysalis longicornis; Babesia bovis; Bovine babesiosis; Pathogen acquisition; Pathogen transmission; Cattle fever
Kocan, K. M., de la Fuente, J., Blouin, E. F., Coetzee, J. F., & Ewing, S. A. (2010). The natural history of Anaplasma marginale. Veterinary parasitology, 167(2-4), 95-107.
Pete D. Teel, Thomas Hairgrove, Transboundary Tick and Tick-Borne Pathogen Threats to Cattle, Veterinary Clinics of North America: Food Animal Practice, Volume 40, Issue 2, 2024, Pages 305-316, ISSN 0749-0720, ISBN 9780443293863, https://doi.org/10.1016/j.cvfa.2024.01.006. (https://www.sciencedirect.com/science/article/pii/S0749072024000082) Keywords: Ticks; Tick-borne pathogens; Disease; Surveillance; Diagnosis; Prompt intervention
Polito, Victoria J., et al. "Tick abundance and levels of infestation on cattle in response to patch burning." Rangeland Ecology & Management 66.5 (2013): 545-552.
Railey AF and Marsh TL (2021) Economic Benefits of Diagnostic Testing in Livestock: Anaplasmosis in Cattle. Front. Vet. Sci. 8:626420. doi: 10.3389/fvets.2021.626420
Regitano, L. C. d. A., Prayaga, K. C., Bishop, S., Axford, R. F. E., Nicholas, F. W., & Owen, J. B. (2010). Ticks and tick-borne diseases in cattle. Breeding for Disease Resistance in Farm Animals, 295-314. https://doi.org/10.1079/9781845935559.0295
Jackson is a master's student and Olds is an assistant professor, both with the Kansas State University Department of Entomology; and Cohnstaedt is a research entomologist with the USDA-ARS Foreign Arthropod-Borne Animal Disease Research Unit. Photo credits: Kansas State University
