The Ixodes tick is the primary vector for spreading the disease. As the tick attaches to the host the Lymes organism migrates from the intestinal tract of the tick to the mouth parts and then into the host. It is likely that this process takes some time for the attached tick to pass the disease; more than 12 hours. This process may have significant implications regarding prevention and control of the disease. The primary transmission of the diseases to dogs is from the bite of an adult tick. No evidence supports transmission from dog to dog. Once the tick begins to feed on the host it continues until satisfied and then falls off. It is therefore unlikely that any tick brought into the house on a dog will bite again after falling off the host.
Most adult ticks in high disease areas of the country are infected with B. burgdorferi . Although the smaller immature stages of the tick appear to carry the disease they seem to be less involved in transmission. The adult tick is active in the fall and form the spring into early summer. The adult tick is moved through the environment via deer and other large mammals. Birds may be significant in moving the tick over long distances.
The life cycle of the Ixodes(Lymes) tick involves laying eggs by the female in the spring. The immature larvae that emerge feed on the white footed mouse. Many of these mice are infected with B. burgdorferi and pass the organism on to the immature larvae. The larvae fall off the mice and molt over winter to emerge as nymphs in the spring. Many of these nymphs emerge infected. The nymph also feeds on the white footed mouse as well as other mammals including humans and dogs. The following fall the nymph molts again to emerge in the spring as an adult infected with the organism. The male and female adult tick feed on the dog and other large animals. The female tick after engorged falls off the host to lay hundreds of eggs in the environment and begin the life cycle over.
Although Lymes disease presents a serious threat to humans it does not present the same risk to dogs. The majority of Lymes disease is confined to several areas of the country; ie. the north central states and the central to north Atlantic region. The movement of dogs although significant does not present the same risk as it does to humans. It appears that in high incidence Lymes disease areas about 2/3's to 3/4' of the dogs are infected with the disease, that is they have high levels of antibodies against B. burgdorferi. Only a small percentage of these dogs that are infected actually come down with signs of the disease. Therefore in areas where the disease is very prevalent a positive test for Lymes antibodies does not indicate recent infection, only that the dog has had some exposure to the disease. The high incidence of infection with a relatively low rate of signs of the disease suggests that dogs seem to tolerate the organism or possibly defend themselves successfully.
The most common sign of Lymes disease in the dog is arthritis affecting more than one joint. Often these are the small joints that are painful, warm and swollen. Many dogs display only a reluctance to move as their only sign of the disease. Other signs include fever, loss of appetite and swollen lymph nodes. Dogs do not appear to have any of the long term complications that afflict humans such as degenerative long term arthritis, serious neurological complications and cardiac problems. Less than rarely have these problems been reported. Also, the skin rash that Lymes is associated with in humans is of minor incidence in dogs. The immune response by the dog to the organism is not clearly understood. The length of infection may persist for quite some time, one to two years before elimination. However, a complete picture of the disease in the dog is certainly forthcoming as data accumulates. The Lymes test does not test for the Lymes organism. Instead, it looks for the antibodies against Lymes. It is also not clear if the use of antibiotics interferes with the immune response to remove the disease. Current theories suggest that the infected dog will build antibodies to remove the organism over a long period of time possibly as long as 1-2 years. Most dogs showing signs of the disease when treated with antibiotics will improve greatly with in 1-2 days. Some of these dogs will recover and several weeks to months later will appear to relapse. However, they seem to respond equally as fast with another treatment of antibiotics. There have been reports of dogs relapsing a third time but these reports are uncommon. SOME INVESTIGATORS HAVE SUGGESTED THAT THESE RELAPSES ARE NEW INFECTIONS implying that infection does not confer immunity or protection. Other investigators propose that the Lymes organism is removed by antibiotics to very low levels, producing improvement in the patient, but never completely eliminated. This would allow a few organisms to repopulate and cause relapse. Nevertheless the vast majority of dogs recover completely and chronic disease is rare.
Good tick control on the dog is probably very effective at controlling Lymes. There are excellent products containing permethrins, amitraz and organophosphates that provide good tick control. Considering that the deer tick needs to be on the host for some time before transferring the organism, this would seem to be a good method of prevention.Several commercial vaccinations also are available against Lymes in the dog. The efficacy of the vaccine's support is primarily anecdotal. Reports in the field suggest good protection decreasing the incidence significantly , possibly as much as 80%, thus lowering the rate from 5% to 1%. Occasional claims of Lymes disease developing in vaccinated dogs have suggested possible vaccine side affects. Good controlled field trials have not been done. Interestingly the vaccination does stimulate a different antibody response than an infection. The Western blot antibody test can differentiate between these antibodies, whereas most antibody tests do not. These are important findings in detection of the disease in a current vaccinate and suggests a need for further study.
