Today's Veterinary Practice

MAY-JUN 2018

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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PEER REVIEWED 12 PARASITOLOGY in North America.5 Then during the early- and mid- 20th century, restrictions were placed on deer hunting, a number of states began restocking efforts and, combined with an increase in natural habitat, there was a marked resurgence in deer populations to an estimated 30 million by 2015. As deer expanded their range and increased their numbers, there was a corresponding increase in tick species closely associated with deer.5 White-tailed deer populations are so important to the long-term survival of A. americanum that exclusion of deer produces a profound impact on this tick species' populations. Another host that utilizes similar habitats and is an excellent host for A. americanum larvae and nymphs is the wild turkey.5 Areas with a deciduous forest canopy and high white- tailed deer and wild turkey populations can have remarkably large populations of A. americanum. However, many other animals can be parasitized by this aggressive tick. Immature A. americanum stages can be found on a variety of ground-dwelling birds and numerous mammals, such as cats, coyotes, deer, dogs, rabbits, raccoons, red foxes, squirrels and humans. Adult A. americanum also feed on a variety of hosts, including cats, cattle, coyotes, deer, dogs, horses, raccoons, sheep and humans. As A. americanum populations expand into new areas, seasonality of ticks found on dogs and cats can change. Nymphs are found from March through September, larvae are frequently encountered in the late summer into the fall and adults are often encountered from late February through early June.5 Because all life stages can parasitize dogs and cats, this means that A. americanum could potentially be encountered on our pets 8 to 9 months out of the year. A. americanum is considered a major vector of veterinary and human pathogens, including feline cytauxzoonosis (Cytauxzoon felis), Ehrlichia chaffeensis (human monocytic ehrlichiosis), Ehrlichia ewingii, Heartland virus, southern tick- associated rash illness (STARI, a Lyme disease–like infection), Rocky Mountain spotted fever (Rickettsia rickettsii), tularemia (Francisella tularensis), red meat allergy in humans and Bourbon virus. Ixodes scapularis I. scapularis (black-legged or deer tick) is widely distributed in eastern and central North America. 5-7 Its distribution is from Florida to Nova Scotia, west into far eastern Manitoba and then south through eastern Kansas into central Texas. Reasons for its expansion are very similar to those for A. americanum, including increased populations of its primary reproductive host (the white-tailed deer), reforestation, and climatic fluctuations. Seasonal activity of I. scapularis varies by geographic region, but larval activity is generally highest in August and September. Larvae attach to and feed on a wide variety of small mammals, including chipmunks, mice and shrews. Larvae also feed on birds and lizards. The white-footed mouse (Peromyscus leucopus) is of particular importance in the tick life cycle and disease transmission because it serves as a good host for larval I. scapularis and is a major reservoir of Borrelia burgdorferi. Immature ticks typically engorge for 2 to 4 days before dropping off to molt in moist, protected areas such as under leaf litter in forested habitats. Larvae overwinter and then molt to nymphs in the spring. Nymphs will feed for 3 to 4 days on a variety of hosts, including birds, cats, chipmunks, mice, opossums, raccoons, shrews, skunks, squirrels and humans. Nymphs are found primarily from May through July in the northern US and in Canada. Adults appear most commonly from October through December. Adults that do not find a host will quest again, typically from March to May. Adults feed for 5 to 7 days, primarily on white-tailed deer, but also on bobcats, cattle, coyotes, dogs, foxes, horses, opossums, raccoons, humans and other mammals.5 I. scapularis is a vector for B. burgdorferi, Anaplasma phagocytophilum (human granulocytic ehrlichiosis [HGE] agent; formerly Ehrlichia equi) and Babesia microti (humans). CONCERNS WITH CURRENT TICK CONTROL MEASURES Although recent pharmaceutical advances have been made in flea reproduction control, such advances in the area of tick control are lacking. With the exception of the brown dog tick, R. sanguineus, our ability to manage tick reproduction is limited, if not almost nonexistent. In most flea infestations, we have the opportunity to control flea reproduction by either killing fleas before they can reproduce or killing flea eggs. However, it is not just because we have effective residual insecticides, insect growth regulators or insect development inhibitors that we are successful. This success is also due in large part to the fact that we can

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