From January 1998 through September 1999, 324 dogs in three northwestern Georgia counties were examined for ticks. Six species of ticks were recovered. The three most commonly collected ticks were the American dog tick, Dermacentor variabilis (Say) (310 ♂♂, 352♀♀; prevalence, 97%; mean intensity 2.1); the brown dog tick, Rhipicephalus sanguineus (Latreille) (118♂♂, 119♀♀, 38 nymphs; prevalence, 22%; mean intensity, 3.8); and the lone star tick, Amblyomma americanum (L.) (8♂♂, 26♀♀, 2 nymphs; prevalence, 5%; mean intensity, 2.4). Other ticks recovered were Ixodes cookei Packard (3♀♀); the Gulf Coast tick, Amblyomma maculatum Koch (2♂♂); and the blacklegged tick, Ixodes scapularis Say (1♀). Another adult female specimen of I. scapularis was recovered from a cat, further reinforcing that this medically important tick is present in northwestern Georgia.
Various tick species have been recorded from Georgia (Wilson and Baker 1972, Durden and McCay 1996), but few quantitative tick studies have been conducted in the northern part of this state. The role of ticks in transmitting pathogens that cause "emerging diseases" like Lyme disease, ehrlichiosis, and human babesiosis has stimulated research on ticks in recent years (Sonenshine 1993). Although 22 species of ticks have been recorded from Georgia, only the lone star tick, Amblyomma americanum (L.); the American dog tick, Dermacentor variabilis (Say); the brown dog tick, Rhipicephalus sanguineus (Latreille); and the rabbit tick, Hemaphysalis leporispalustris (Packard) appear to be common throughout the state (Wilson and Baker 1972). Some other tick species of medical and veterinary importance such as the blacklegged tick, Ixodes scapularis (Say); the Gulf Coast tick, Amblyomma maculatum (Koch); and I. cookei (Packard) have been reported mainly from the southern or coastal regions of Georgia (Wilson and Baker 1972, Durden and Oliver 1996).
Recently I. scapularis, the major vector of the Lyme disease agent in the eastern United States, was reported from counties in Tennessee and Alabama that border northwestern Georgia (Dennis et al. 1998). These findings, combined with the increase in population densities of potential hosts of I. scapularis such as white-tailed deer, Odocoileus virginianus (Zimmermann) (Dennis et al. 1998), and possibly also of white-footed mice, Peromyscus leucopus (Rafinesque); cotton mice, Peromycus gossyninus (Le Conte); cotton rats, Sigmodon hispidus Say & Ord, and recent reports on global warming, motivated our decision to conduct a survey of ticks parasitizing dogs in northern Georgia. To date, Lyme disease and its main eastern vector, I. scapularis, have not been recorded from northwestern Georgia (Oliver 1996, Dennis et al. 1998). The objectives of this survey were to compare the presence of tick species with earlier tick records from this region (Wilson and Baker 1972) and to determine if I. scapularis was present in northwestern Georgia
Materials and Methods
Ticks were collected from dogs by the resident veterinarian at four veterinary clinics from three counties—Gordon County (Calhoun), Bartow County (Cartersville), and two clinics from Floyd County (Rome). Dogs (n = 324) which were brought to the clinics for various reasons were checked by veterinarians or their staff for ticks. Ticks were removed and placed in vials containing 70% ethanol. They were then taken to the laboratory to be identified. The survey was conducted between January 1998 and September 1999.
Three species of ticks were collected regularly during the summer from dogs (Tables 1 and 2). Dermancentor variabilis was the most common species (662 ticks from 315 dogs; prevalence of dogs infested, 97%; mean intensity = mean number per infested dog, 2.1), followed by R. sanguineus (263 ticks from 71 dogs; prevalence, 22%; mean intensity, 3.8), and A. americanum (36 ticks from 15 dogs; prevalence, 5%; mean intensity, 2.4). Details on numbers and stages collected for each tick species by county are presented in Table 1.
In addition to the three common tick species, Ixodes cookei, (3♀♀), A. maculatum, (2 ♂♂), and I. scapularis (1(♀) were found on the dogs. One additional female specimen of I. scapularis was recovered from a cat.
Of the two major tick species we collected, D. variabilis was active throughout the summer (May to August) whereas R. sanguineus was abundant mainly during the latter part of summer (July and August) (7.6 and 8.7 ticks per dog, respectively) as shown in Table 2. In most cases, dogs were infested with one species of tick. Most animals were infested with D. variabilis or R. Sanguineus, but seldom with both.
Results of this survey conducted in three counties in northwestern Georgia confirm the findings of Wilson and Baker (1972).Dermacentor variabilis and R. sanguineus were the predominant species of ticks found on dogs in this region. However, we also report I. scapularis for the first time from northwestern Georgia. One specimen was recovered from a dog in late August and another was removed from a cat in January. Although it is considered early to find I. scapularis in August, adults of this tick have been collected in southern Georgia in September (L.A.D., unpublished data) and it is feasible that a few adults could be questing in late August, especially in the cooler regions of northern Georgia.
In Oklahoma and Arkansas, Koch (1982) reported the same six species of ticks that we recorded as ectoparasites of dogs. However, he found A. americanum to be the most prevalent tick with 72% of 870 dogs infested, followed by R. sanguineus (71%), D. variabilis (24%), and I. scapularis (21%). Clearly, D. variabilis was much more prevalent on dogs (97% infested) in our study, whereas A. americanum, R. sanguineus, and I. scapularis were more common in Koch's (1982) survey. Also, Koch (1982) reported intensities of 53.6 and 30.7 for R. sanguineus and A. americanum respectively, which are much higher than the mean intensities that we recorded for these two species. However, the mean intensity of 2.1 that we recorded for D. variabilis is slightly higher than the intensity of 0.8 reported by Koch (1982) for this species.
A survey of ticks parasitizing dogs in the upper Coastal Plain of South Carolina (Clark et al. 1996) also recorded six species of ticks with five of these shared with species recorded in our survey. The exception, I. cookei, which we recorded, was replaced by Ixodes affinis Neumann in the South Carolina survey. In North America, I. affinis is confined to the Coastal Plains of Florida, Georgia, and South Carolina, and does not occur in northern Georgia (Durden and Keirans 1996). Prevalences and intensities of parasitism by A. americanum, D. variabilis, and R. sanguineus were similar in our study and in the South Carolina survey, but both A. maculatum and I. scapularis were more common on dogs in the South Carolina survey.
The geographical distribution and abundance of I. scapularis have apparently increased in recent years (Dennis et al. 1998). One reason for this is probably the increase in white-tailed deer population densities (Dennis et al. 1998), a major host of adult I. scapularis. Increased population densities of this host serve as an amplifying factor, resulting in an increase in tick numbers in nature.
The observation that dogs were rarely infested by more than one speeies of tick substantiates assumptions that ticks are often found in clumps in nature. Such an aggregated distribution might be advantagous for ticks by enabling a few adults to parasitize the same individual host, thus promoting mating which takes place on the host after an initial period of blood intake in multistriate ticks (Amblyoma, Dermacentor, and Rhipicephalus in this survey).
Comparing our results with previous data suggest that further studies in northern Georgia, particularly with respect to wild animal hosts, should be conducted.
The authors thank Dan Pate (West Rome Animal Clinic), Richard Dixon (East Rome Animal Clinic), Richard Moore (Cartersville Animal Medical Center), and Bruce Stansell (Gordon County Animal Hospital) for collecting ticks, and Bruce Conn, Dean of School of Mathematical and Natural Sciences, Berry College, GA, for his support and encouragement.