LYME DISEASE
Lyme disease is a bacterial infection that affects many systems in the body. It is transmitted by tick bites and has become the most common arthropod-borne, human disease in the United States.
ETIOLOGY: BACTERIAL
Borrelia burgdorferi is the bacterium responsible for Lyme disease. It is a spirochete, which means it is a spiral-shaped bacterium that is longer than it is wide. B. burgdorferi has very specific growth requirements in the laboratory, so it is not routinely cultured.
HOSTS
The two primary reservoir hosts for B. burgdorferi are white-footed mice and whitetail deer. Even though the ticks bite the deer, the deer do not become infected, but they serve as means of survival and transportation for the ticks. Humans and other animals, such as dogs, cats, horses, and cattle, can also become infected with B. burgdorferi.
TRANSMISSION
Ticks transmit B. burgdorferi through their bites, from one host to another. The organism lives in the intestinal tract of the tick and can be passed from host to host when the tick feeds. It takes 24 to 36 hours after a tick becomes attached to its host before it starts releasing B. burgdorferi.
The tick life cycle has three active stages after the egg hatches: larva, nymph, and adult (see Appendix 1). The larva must have a blood meal before it can molt to the nymph stage, and the nymph must have a blood meal before it can molt to the adult stage. A tick at each active stage can become infected when it takes a blood meal. The bacteria stay with the tick when it molts to the next stage. As it feeds before molting, a tick at each stage can infect another animal by depositing B. burgdorferi at the site of its bite. Typically the larva will feed on small rodents, like the white-footed mouse. If the mouse was infected, the larva becomes infected. Nymphs prefer feeding on many animals, such as small rodents, dogs, cats, horses, cattle, and humans. Similarly, if any of these animals were infected, the nymph would become infected. Adult ticks prefer to feed on whitetail deer. The life cycle takes 2 years to complete. Ticks can feed on people at any of the three stages (Figure 26).
Two ticks that can transmit Lyme disease to humans have been identified: the black-legged deer tick, Ixodes scapularis, in the northeastern and north central United States, and the western black-legged tick, Ixodes pacificus, on the Pacific coast of the United States. The larvae of both black-legged ticks are the size of a pin head and are tan colored. The nymphs are the size of a poppy seed and are beige or semitransparent. The adults are about the size of an apple seed and are black or reddish (Figure 27). For Lyme disease to occur, there must be B. burgdorferi, white-footed mice, and whitetail deer in an area.
Dogs and cats can get Lyme disease but cannot transfer it directly to people. They can, however, transport ticks into a home, yard, kennel, or veterinary facility.
Not all black-legged ticks are infected with B. burgdorferi. In some areas less than 1% of the ticks are infected, but in other areas over 50% are. B. burgdorferi can infect other species of ticks, but none of them have been shown to transmit Lyme disease to humans.
LYME DISEASE IN ANIMALS
Many animals infected with B. burgdorferi do not develop clinical signs. If they do develop an illness, it may be a long time after the initial infection.
CATS
Cats that develop Lyme disease usually display fever, anorexia, lethargy, lameness, and irregular breathing. There is nothing about these symptoms that is specific to Lyme disease, so many cases will go undiagnosed.

Stay updated, free articles. Join our Telegram channel

Full access? Get Clinical Tree

