Tick Borne Diseases

Spring with its garden of delights also brings a host of unwanted creatures bent on bringing dogs and people to their knees. We are particularly reminded of this since one of our family is already on antibiotic therapy, being treated for Lyme Disease, and at this writing it is only April. This comes as a warning against complacency, no matter how cold the weather seems to be.

The most common carrier of the spirochete which causes Lyme Disease is the black legged or deer tick, a creature so small as to be almost invisible in its early stages of development. This tick may survive freezing conditions and contrary to its name, the principal reservoir of the disease is the white-footed mouse where it develops in its larval stage. This tick needs three hosts for its life cycle, which extends over a two year period. The adult stage of the tick is most abundant in the United States in early spring and fall and its natural host is the white tailed deer. It is generally thought that an infected tick must feed on the host for 12 to 24 hours before the spirochete is transmitted. However, more recent studies have shown that at 12 hours a person or animal has a 25% chance of being infected. By 24 hours that rises to 50% and by 48 hours the recipient has a 100% chance of being infected by a tick carrying the disease.

In humans a rash may appear as early as a few days to four weeks following a tick bite. However, not all people develop a rash and some develop secondary skin irritations in addition to symptoms resembling the flu. Dogs do not generally develop a rash but they may develop malaise, joint pain, fever and lethargy. The organism may spread throughout the body and affect multiple organs and tissues, including the brain, heart, nervous system and synovial tissue in the joints. Signs may appear almost immediately or not until months to years after the initial infection.

Diagnosis is difficult because the level of the serum antibody titer does not appear to correlate with the degree of clinical illness.

Dogs left untreated following experimental infection experienced one to two episodes of lameness with or without joint swelling over several months. Antibiotic treatment with doxycycline or amoxicillin for 30 days alleviated or prevented development of clinical signs. However, the infection was not completely resolved in all dogs as some of the infectious organisms rebounded and additional antibiotic treatment was needed.

Labrador and Golden Retrievers appear to be predisposed to a type of Lyme Disease infection which causes a unique form of glomerulonephritis referred to as Lyme nephritis. It is immune-mediated and causes a rapidly progressive protein-losing nephropathy and renal failure and is fatal. Dogs with Lyme nephritis have more acute onset of signs and much more rapid progression of disease than dogs with other types of renal problems. It sometimes mimics acute pancreatitis with vomiting, lethargy, bleeding into the skin of the abdomen, lameness and tenderness of the abdomen.

There is controversy about the effectiveness of annual Lyme Disease vaccination. It is really a matter of choice whether or not to vaccinate. Lyme vaccines have not proved to be 100% effective and it is perhaps as useful to administer one of the topical preventatives, but that is a decision to be made between client and veterinarian. Until recently it was impossible to determine whether a vaccinated dog had been subsequently infected, but a new test can differentiate between the two.

Lyme Disease is not the only tick borne illness. Ehrlichiosis is the other major disease. It is carried by the brown dog tick and while it used to be confined to the southwest it is now seen in many parts of the country, including the northeast, far west, with scattered pockets in the upper midwest. There is no vaccine against ehrlichiosis but the treatment with doxycycline is the same as for Lyme Disease.

Another tick borne disease is Rocky Mountain Spotted Fever. As one might suspect, this pest used to be confined to the region bearing its name, but that is no longer the case. Symptoms are the same for this disease, causing lameness, fever, lack of appetite and general malaise as for the other diseases. Blood tests can sometimes find the pathogen, but often antibody reactions have to be the determining factors in which type of tick disease the dog is carrying.

In treating all tick borne diseases it is essential to continue the antibiotic therapy for a sufficient period of time (at least 3 weeks) to be sure that the disease carrying pathogens have been killed. (Veterinary Technician, April 2001, DVM Newsmagazine, April, 2001)

Zoonotic Risks of Parasites

Internal parasites pose a risk not only to dogs which carry them but also to their owners. The most common internal parasites in dogs are roundworms (toxocara cants) and hookworms (ancylostoma caninum). Both may be transmitted from dam to puppies through the placenta or through the milk. They may cause serious disease in young animals and also contaminate the environment when the eggs are shed. Eggs are not shed by puppies until they are 2 to 3 weeks of age so treatment for them is not usually started until the parasite burden has grown and the eggs enter the environment. Most owners do not worm their puppies until they are 6 or 8 weeks of age which is late according to recommendations from the American Association of Veterinary Parasitologists and the Centers for Disease Control and Prevention. They prescribe a fairly rigid and extensive protocol. It is: Puppies should be wormed every two weeks until they are 3 months of age, then monthly from 3 to 6 months and 4 times a year after six months. Adults should be treated regularly depending upon the exposure of the animal. Bitches should be wormed once before mating, once at parturition and once at 2 months and then 4 weeks after giving birth.

Humans become infected with roundworms through exposure to the feces either by handling puppies which are infected or through the environment where eggs may be dormant. Parasites usually migrate through body tissues. Unlike parasites in dogs which tend to remain in the intestines to mature, they may lodge in other organs causing allergic responses, neurologic damage or blindness. Common symptoms in humans include abdominal pain, weakness, lethargy and wheezing.

Humans can acquire hookworm infection through ingestion or laval penetration of the skin. The most common sign of this parasite is the itchy skin pattern created by migrating larvae. Larvae may also enter the small intestines producing enteritis.

Tapeworm is another internal parasite which may be transmitted to humans through the ingestion of a flea or by eating infected animals such as rabbits.

People most susceptible to zoonotic parasitic infections are young children, people in the household with puppies, those who are careless about sanitation, those who work in close contact with animals, including wildlife, people with compromised immune systems and veterinary professionals.

Careful attention to hygiene, keeping clean, picked-up kennel, yard and house environments and only allowing children to run barefoot in areas which are known to be free of contaminants are simple rules to lessen the possibility of zoonoses. (Veterinary Technician, April 2001).

By Connie Vanacore