Lyme Disease

We have a local resident, the deer tick, Ixodes pacificus, who generally hides out in the summer and then about the time the rains return, little hatchlings crawl out of previously deposited eggs to look for their first blood meal around the time of Halloween. These are called larvae, are about the size of the head of a pin, and have only six legs. They preferentially seek out small rodents and lizards. After obtaining a blood meal, the larvae will molt into an eight-legged nymph whose food preference is more generalized to include small to medium or even large mammals including people. Again after a blood meal the nymph will molt into an adult that will feed on larger mammals, especially deer and frequently dogs, cats and humans. In this tick species only adult females will feed and engorge (the tick abdomen fills with blood). The Adult male’s only role is mating. This tick has a two year cycle and so nymphs and adults are also appearing in the fall and tend to stick around until mid-spring.

Ticks can be vectors of a variety of bacterial and viral diseases depending on the species of tick and the geographical location. In our area, Lyme disease is a concern. We are more fortunate than the New England or Great Lakes regions in terms of the prevalence of Lyme disease (named for Lyme, Connecticut). There are about 300,000 cases a year in humans, most of them from these two areas, but we are third. There is some evidence that ticks feeding on western lizards may imbibe a substance that is toxic to the Lyme Disease organism. This may be a factor that substantially lowers the infection rate in California compared to the northeastern United States. We should be grateful to the lizards.

The causative agent of Lyme Disease is Borrelia burgdorferi, a spirochete (spiral) bacterium. When an uninfected larvae feds on an infected small rodent, they acquire this agent and then may pass it on to the next host fed on as a nymph. If a nymph is uninfected, it may pick up this disease when feeding on an infected mammal, and then molt into an infected adult, possibly passing it on to the next victim. While there are a large number of mammalian reservoir hosts, it appears that dogs and humans are almost exclusively the species afflicted by Lyme disease. There are many cases of seropositive individuals who nonetheless do not develop actual disease. Apparently even if bitten by an infected tick, most dogs and people do not develop disease because their immune system defeats it. So a positive antibody titer for Borrelia does not require treatment unless there are clinical signs. The primary clinical sign in dogs is lameness and possible joint swelling. In humans a bulls-eye rash may appear as the first sign 3-30 days after the tick bite. Days to weeks after the onset of localized infection, the disease may go on to resemble flu-like symptoms and can involve the brain, nerves, eyes, joints and heart.

There is a successful treatment for genuine cases with an antibiotic called doxycycline. Preventing tick attachment is the best defense. Removing attached ticks within 24-36 hours would likely prevent transfer of the bacteria. Tick removal would entail grasping the tick as close to the skin as possible with a tweezers or gloved hand and pulling slowly straight out. Twisting would break off mouth parts, burning with a match causes the tick to expel saliva into the host. Avoid crushing the tick as it will release possibly infectious material.

Very effective new products (inhibitors of the arthropod nervous system) are available to quickly dispatch feeding ticks. These products are also very effective against fleas. These are oral products for dogs, either once a month, Nexgard (Afoxolaner), or once every three months, Bravecto (Fluralaner). In cats the product is topical Bravecto which is effective for three months for fleas and 2-3 months depending on the species of tick. There are no products which reliably repels ticks before they attach.

One other tick is commonly found in our area. This is the wood tick, Dermacentor occidentalis, not a vector of Lyme Disease, but can cause Tick Paralysis in dogs and humans. This tick is much larger than the Deer Tick, appears in late winter to early spring and persists until the beginning of summer. Both males and females of this species feed, although the males cannot engorge. The previously mentioned products are also effective against this tick. Both Nexgard and Bravecto offer either a free sample or rebates. Pinecreek Veterinary Clinic has had great success with both products and highly recommends them as being the best product available for ticks, a notoriously difficult arthropod to kill. We have so far not seen adverse reactions in treated animals.

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