The expansion in tick populations has led to an increased risk of infection for humans and animals with both established tick-borne agents and newly recognized ones, creating a serious One Health problem.
Infections transmitted by ticks are increasingly recognized as important causes of disease in humans and pets in North America, said Susan Little, DVM, PhD, DACVM (parasitology), Regents Professor of Parasitology, Oklahoma State University, Stillwater, in a recent US Centers for Disease Control and Prevention (CDC) Clinician Outreach and Communication Activity webinar.
Indeed, the US Department of Health and Human Services (HHS) recently announced the appointment of 14 members to the new Tick-Borne Disease Working Group. This group will provide expertise to help HHS in its efforts to identify unmet needs and research priorities in tick-borne diseases (TBDs), to improve federal coordination of efforts related to this serious public health problem.
Although ticks were first shown to be responsible for transmitting disease at the end of the 19th century, TBDs have significantly emerged and expanded in recent decades, and several novel infections have been identified.
Dr. Little noted that the last 3 decades have seen a dramatic rise in the number of certain species of ticks and their geographic distributions worldwide. The expansion in tick populations has led to an increased risk of infection for humans and animals with both established tick-borne agents and newly recognized ones, creating a serious One Health problem.
The introduction of infections to humans in new geographic locations can “catch local physicians off guard because they are not used to seeing certain TBDs in their local areas,” said Dr. Little.
Although the media tends to place much of the focus of TBDs on Lyme disease, Dr. Little stressed that ticks also transmit many other different pathogens. In addition to other bacteria, they also transmit helminths and protozoa. And “we’re learning more, especially in recent months, about viral transmission,” she added.
Dr. Little highlighted several challenges to controlling tick populations.
Several factors have contributed to the expanding geographic range of many ticks, she said, including changes in climate and habitat. Similarly, the presence of ideal environmental conditions and plentiful wildlife reservoir hosts have allowed numbers of ticks to increase.
Dr. Little discussed some of the most common tick species associated with dogs in North America. These are 3-host ticks, she noted: each tick developmental stage feeds on its host and then detaches, molts in the environment, and then reattaches to a new host in the next stage. These ticks include the Lone Star tick (Amblyomma americanum), Gulf Coast tick (A. maculatum), American dog tick (Dermacentor variabilis), wood tick (D. andersoni), blacklegged tick (Ixodes scapularis), deer tick (I. pacificus), and the brown dog tick (Rhipicephalus sanguineus).
According to Dr. Little, the tick stages of the brown dog tick have a strong host preference for dogs and are found everywhere where dogs exist. “They are truly a dog phenomenon,” she said. Although these ticks can survive outside, they can also survive indoors and may produce massive infestations in homes that cause serious problems for humans and dogs. These indoor infestations can be difficult to eradicate and can be catastrophic, Dr. Little stressed, adding that owners should expect that environmental treatment efforts will take at least 6 months to eliminate this tick from indoor premises.
The stages of the other tick species may occur on a variety of different wildlife hosts and other animal hosts, she said. Typically, these ticks exist and thrive on wildlife in their natural habitats, so the tick populations tend to increase when the wildlife populations increase.
Scientists and clinicians face significant challenges in controlling these tick populations, said Dr. Little. “Geographic expansion is a huge challenge to tick control,” she emphasized, adding that scientists’ ability to limit tick reproduction is also limited.
“Tick myths and misperceptions” also pose challenges to tick control, said Dr. Little. In veterinary medicine, these include underestimation of the risk of infestation for some pets. For example, although most people are by now aware of the risk of tick infestation for dogs, they may not be aware of the risk for cats and thus may not be using any tick control products on their cats.
Dr. Little recommended some strategies to limit TBD transmission to humans and animals in the face of increasing risk of tick infestations.
The ideal strategy is to protect the skin, she said. People should wear protective clothing when walking in tick-infested areas, and should regularly perform skin checks for ticks on themselves and on their dogs. Dr. Little advised using the “pick them and flick them” approach to removing ticks from the skin.
“All dogs should be on tick prevention products all year round,” said Dr. Little, not only for the dog’s benefit, but also as a public health recommendation. She noted that a vaccine is also available for canine Lyme disease. Dr. Little also discussed other helpful strategies for tick control, including preventing pets from roaming, limiting tick habitats (by removing leaf litter and burning debris, for example), excluding and discouraging wildlife from yards and homes, and treating wildlife for ticks.
Dr. Little emphasized that pets are at low risk for TBDs if they receive regular veterinary care and if their owners follow tick prevention recommendations. So, simply having pets does not increase the public health risk for TBDs in people, she noted.
“The good news is that comprehensive tick control is really the best way to minimize the risk of tick infestation” for people and pets, concluded Dr. Little.
Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.