Ticks are now a common topic of conversation among Canadian veterinarians. We have seen rapid changes in the abundance, distribution, and activity of several tick species, in part because of climate change. The greatest focus has been on the blacklegged tick (Ixodes scapularis), which has expanded its range into many areas of Canada. Although blacklegged ticks certainly deserve the attention, the time has come to shed some light on another tick species—the brown dog tick—which has been crawling below the radar.
A closer look
The brown dog tick (Rhipicephalus sanguineus) is a three-host hard tick with worldwide distribution, predominately in tropical and subtropical areas, as well as warmer temperate regions.1 This species is believed to have originated in Africa and was subsequently transported to new locations via domestic dogs.2 This process continues to this day.
Indeed, studies conducted at the Ontario Veterinary College (OVC) reveal the vast majority of dogs with reported brown dog tick bites have a history of travel. In a small number of cases, this exposure was attributed to a pet accompanying their owner on vacation; however, most submissions were from dogs that had been rescued internationally, mainly from locations in the southern United States and the Mediterranean basin.
Rescuing dogs from abroad has become a growing practice in Canada—and, currently, there are minimal import requirements for these animals.3 Given the relatively long feeding duration of a brown dog tick (five to 21 days for adult females1,2), it is possible for a dog to be transported a long distance and be rehomed before the tick is even finished its meal! This is where the issue begins.
Brown dog ticks are unique in they can survive in areas of low humidity, such as a house, kennel, or veterinary clinic.4 Once feeding is complete (this occurs during each life stage), these ticks will leave their host and hunker down in a small crevice or crack where they will either moult to the next life stage or—in the case of an adult female—lay thousands of eggs.1,2
The lifecycle of this species can be quite fast, especially in warm areas; development from egg to larvae to nymph to adult can occur within three to six months.4 It is common for most activity to go unnoticed, especially since approximately 95 per cent of their life is spent off the host. Thus, by the time ticks are repeatedly noticed on a dog, there is typically already a massive infestation in the home. When this is extreme, it is not uncommon to see ticks crawling up walls, on furniture, and across the carpet.2
Unfortunately, it is suspected many of the submissions of brown dog ticks to our studies have been associated with home infestations. Suspicion arises if the most recent history of travel was several months prior, or if a dog repeatedly presents with ticks (particularly in the winter months when activity of our established tick species is low). Other countries have also sounded the alarm on the risk of introducing brown dog ticks through dog importation and travel, including researchers in the United Kingdom.5
Infestations on dogs can be highly variable. One canine may have only one or two ticks, while another could have hundreds (or thousands).1,2 These parasites are commonly found in warm and protected areas on the dog, including inside the ears, under the forearms, in between the toes, and in the inguinal area. Younger canines appear to be at higher risk of infestation, and ticks seem to have some breed preferences.1,2
Although dogs are the primary target, these ticks will also bite humans. There seems to be a growing number of reports of human brown dog tick bites—particularly when the infestation level is heavy or temperatures are high.1,2
In addition to the nuisance posed by infestations, brown dog ticks are notorious vectors of several pathogens of human and animal health significance: Ehrlichia canis (canine ehrlichiosis), Babesia canis (canine babesiosis), Rickettsia rickettsii (Rocky Mountain spotted fever), and R. conorii (Mediterranean spotted fever) are just some on the list, with the latter two being zoonotic.2 The risk of these pathogens varies widely by geography and, thus, would be related to the region from which the dog came.
Where to begin?
Because this species is not native to Canada and recent travel history is not always apparent, brown dog ticks may not be on a veterinarian’s radar. Further, their small size and inornate dark brown appearance might also make them easily mistaken as blacklegged ticks by the naked eye.
Assessing potential risk of brown dog ticks starts with a thorough history, including past travel. Indeed, travel from any tropical, subtropical, or warm temperate zone of any dog in the house (including potential visiting dogs) is one indicator.
A thorough examination of the dog should be conducted and, if ticks are discovered, these should be viewed under a stereoscope (or compound microscope on low power). Brown dog ticks have a characteristic hexagonal-shaped basis capituli that makes them easy to differentiate from other common species of ticks (Figure 1).
If found on a dog immediately following travel, the first step is to use a parasiticide with efficacy against brown dog ticks. Because these are non-native parasites, some products sold in Canada are not licensed for this tick species. In this case, a conversation with the veterinary technical specialist of the pharmaceutical company may be indicated.
Following treatment, the owner should be advised to monitor for any additional tick bites and return to the clinic if they are noted, as this may indicate the presence of an in-home infestation (the same may be true if brown dog ticks are found on a dog more than a month after travel). In these scenarios, treatment of the dog and the environment is required.1,2 A specialist in household pest management will need to be consulted for environmental management, as treating the pet alone will not be sufficient to eliminate the infestation.
Level of concern
Given the current climate of Canada, wide establishment of brown dog ticks is believed to be low risk. Laboratory studies show development from one life stage to the next requires consistent temperatures above 10 C (50 F).4 Future studies are needed to assess if this risk may evolve with climate change. That said, because these ticks have strong preferences for indoor environments, local establishments—including in homes, kennels, and veterinary clinics—is occurring now, making client education paramount.
The brown dog tick is just one example of the health risks associated with importation of (or travel with) dogs. Discussion on the risks and mitigation measures with local rescues and prospective owners prior to adoption is a necessary step in ensuring this process is safe for everyone. Rescuing dogs from situations of poor animal health and welfare is a practice generally driven by philanthropic goals and many individuals have provided dogs with forever, loving homes—it’s just better for everyone if the home is not shared with a thriving colony of brown dog ticks.
Katie Clow, DVM, PhD, is an assistant professor in One Health in the department of population medicine at the Ontario Veterinary College (OVC), University of Guelph. Her research focuses on the ecology and epidemiology of vectors and vector-borne zoonoses, with a specific emphasis on the blacklegged tick and Lyme disease. Dr. Clow can be reached at firstname.lastname@example.org or through her website katieclow.com.
1 Dantas-Torres F. Biology and ecology of the brown dog tick, Rhipicephalus sanguineus. Parasites and Vectors. 2010;3(1):1-11. doi:10.1186/1756-3305-3-26
2 Dantas-Torres F. The brown dog tick, Rhipicephalus sanguineus (Latreille, 1806) (Acari: Ixodidae): From taxonomy to control. Vet Parasitol. 2008;152(3-4):173-185. doi:10.1016/j.vetpar.2007.12.030
3 Canadian Food Inspection Agency. “Travelling with your dog: import rules” https://inspection.canada.ca/animal-health/terrestrial-animals/imports/import-policies/live-animals/pet-imports/dogs/eng/1331876172009/1331876307796. Accessed March 30, 2021.
4 Koch HG, Tuck MD. Molting and Survival of the Brown Dog Tick (Acari: Ixodidae) under Different Temperatures and Humidities1. Ann Entomol Soc Am. 1986;79(1):11-14. doi:10.1093/aesa/79.1.11
5 Hansford KM, Phipps LP, Cull B, Pietzsch ME, Medlock JM. Rhipicephalus sanguineus importation into the UK: Surveillance, risk, public health awareness and One Health response. Vet Rec. 2017;180(5):119. doi:10.1136/vr.104061