(Figures 5-05 to 5-18)
The hard ticks represent some 13 genera and about 650 species. Most of the hard ticks are tropical, thus, infestations with these parasites more commonly occur in warmer climates. The different stages of hard ticks are often less fastidious in their choice of hosts than are the soft ticks, and often cats can become infested with larvae, nymphs, or adults of species of these parasites that are more commonly found on other domestic animals or wildlife. Due to the large number of species involved, the ticks will often not be identified beyond being recognized as a hard tick or as being one of the more common genera.
The fact that ticks feed on the tissue fluids of their hosts allows them to serve as vectors of disease. Cats are sometimes infected with other pathogens by the bite of a tick, for example, Cytauxzoon, which the tick obtains while feeding as a larva or nymph.
The common ticks parasitic on dogs and humans often are also found on cats. Those genera which are most often observed are Ixodes, Dermatobia, and Rhipicephalus. Other genera that sometimes occur on cats are Haemaphysalis and Amblyomma. Some of these are one-host ticks, some are two-host ticks, and some are three-host ticks. This terminology deals with hosts relative to the occurrence of molting. In the case of hard ticks, there are three distinct stages, the larva that hatches from the egg (Fig 5-05) (it feeds one time), the nymphs which develops from the larva (it feeds one time), and the adult which develops from the nymph (the adult female feeds only one time; adult males feed little if any usually). Thus, in the case of one-host ticks, all stages feed on the same host without falling off to molt. In the case of two host ticks, the larva and nymph feed on one host, and the adult on a second host. Finally, in the case of three-host ticks, the larva feeds on one host and falls off, the nymph feeds on a second host and falls off, the adult feeds on a third host. For cats, almost all the species of importance are one-host ticks. Rhipicephalussanguineus the Brown Dog Tick, which will feed on cats, is a three-host tick, but all stages in the life cycle prefer to get back on a dog to feed after they have molted.
Ixodes. There are some 250 species of ticks in this genus. Ticks of the genus Ixodes have a preanal groove or arch, the scutum is not ornamented, and they have neither eyes nor festoons. Examples include Ixodesdammini with larvae (Fig. 5-05) and nymphs (Fig. 5-06) that feed on rodents and adults that feed on deer (Fig. 5-07). Ixodesdammini is found in the northeastern United States (many consider this species a synonym of Ixodesscapularis). It is often the nymph of this species that bites people to transmit Lyme disease (Fig. 5-08). The European counterpart is Ixodesricinus. These ticks transmit various Babesia and Borrelia species. Ixodesscapularis has larvae that feed on lizards, nymphs that feed on lizards and rodents, and adults that feed on deer. This tick is found in the southeastern United States. In the western United States the counterpart tick is Ixodespacificus which feeds on rodents as larvae and nymphs and mule deer as adults.
Figure 5-05. Ixodesdammini. Two larvae that have just hatched from eggs.
Figure 5-06. Ixodesdammini. Nymph.
Figure 5-07. Ixodesdammini. Engorged female. There are eggs sticking to each of the two most anterior legs.
Figure 5-08. Ixodesdammini. Nymph feeding in a persons arm.
Dermacentor: There are only about 30 species of tick in this genus. The scutum of a typical Dermacentor is ornamented (One species Dermacentor nitens, the tropical horse tick of the southeastern United States, has a scutum that is not ornamented). Ticks that are members of the genus Dermacentor have eyes and festoons along with a rectangular basis capituli (Figures 5-09 to 5-12). Dermacentorvariabilis, the American dog tick, has larvae and nymphs (Fig. 5-013) that feed on rodents and adults that prefer dogs but will attack cats or people. These ticks are mainly found in the eastern United States and serve as the vectors of Rocky Mountain Spotted Fever. In the Rocky Mountains, this tick is replaced with Dermacentorandersoni which transmits the rickettsia in that area.
Figure 5-09. Dermacentorvariabilis. Dorsal view of adult female.
Figure 5-10. Dermacentorvariabilis. Ventral view of adult female.
Figure 5-11. Dermacentorvariabilis. Dorsal view of adult male.
Figure 5-12. Dermacentorvariabilis. Ventral view of adult male. Note that the first coax, segment of the leg that attaches to the body, of the legs get larger as they progress from the anterior to the posterior of the body.
Figure 5-13. Dermacentorvariabilis. Nymph
Amblyomma. This genus of 100 or so species of ticks mainly is found in the tropics. These ticks have an ornamented scutum, eyes and festoons, and relatively long mouthparts. Amblyommaamericana, the Lone Star Tick, is found in the southern United States, and is a three host tick that shows very little host preference in any stage. The common name, the Lone Star Tick, is derived from the single white spot that appears on the back of the female (Fig. 5-14). These ticks are sometimes found quite far north and have been recovered from dogs in New York and New Jersey. Some of the tropical species such as Amblyomma variegatum, which is found in Africa and the Carribean islands, has a very ornate and colorful scutum (Figure 5-15).
Figure 5-14. Amblyommaamericana. Adult female showing the scutum with a single white mark.
Figrue 5-15. Amblyommavariegatum. Scutum of adult male showing the highly ornate scutum. The black and white image does not do justice to the beautiful colors present on this tick.
Rhipicephalus. This group of around 60 species is mainly found in Africa. However, the Brown Dog Tick, Rhipicephalussanguineus, has traveled from East Africa to almost everywhere dogs have. This has been accomplished by the ability and desire of the larvae and nymph to all be capable of feeding on dogs. Thus, this three-host tick has all hosts represented by the same species. This tick will, however, also feed on cats if they are within the same household. Species of Rhipicephalus have no ornamentation, have eyes and festoons, and a basis capituli that is hexagonal (giving the tick its name “fan head”). The males of this genus also have adanal shield that are quite obvious on living uncleared specimens. This tick does not do well in cold weather, but has been domesticated to the point where it can happily undergo its entire life cycle within a house as long as there is a dog present to supply meals.
Figure 5-16. Rhipicephalussanguineus. Adult female/
Figure 5-17. Rhipicephalussanguineus. Dorsal view of adult male.
Figure 5-18. Rhipicephalussanguineus. Ventral view of Adult male. Note the two dark adanal plates on each side of the anus at the posterior of the body.
Haemaphysalis. This is a rather large group of 150 or so species. Only two of these species are found in the United States. Both these species are characterized by have no ornamentation of the scutum, having festoons but no eyes, and a characteristic flaring of the second palpal segment that gives the head a rather triangular appearance. Haemaphysalisleporipalustris is typically found on rabbits, but occasionally it gets on cats. Similarly, Haemaphysalischordeilis usually infests birds, but it will also occasionally get onto cats.