RESERVOIRS & CYCLES OF INFECTION IN THE CENTRAL INTERIOR OF BC

by Ron Gerhardi - with special thanks to Susan for all her help.

The authors of this site would like to thank Dr. E. Murakami for writing The Silent Unnoticeable Cry in the Area. His article inspired the BC Lyme site. We are grateful to him for speaking on our local radio station in Prince George; thereby helping northern residents be more aware of Lyme Disease.

Little is known about Lyme Borreliosis in the Central Interior of BC, which has a large rural population. Ultimately, knowledge will come from persons reporting infection in the area. Education and research are the answer to coping with this disease. This speculation is based on the fact that migratory birds, including ground-foraging birds, are carriers of infection as are some of the ticks that migrate on them.

This means that an uninfected tick can attach to an infected robin that is migrating. After feeding and dropping off, the tick may be infected with Lyme Disease. In spring, infected birds, carrying ticks migrate north from the US, and in the fall, possibly carrying a different strain of disease, migrate southward again. Studies have shown that of all near-domestic species of birds, robins carry approximately 75% of the feeding larvae. Birds have an immune system that enables them to recover from the disease (in the case of robins, about three months).

The best-studied cycle of infection is probably the deer, white-footed mouse and the deer tick. In Ontario the tick vector is Ixodes scapularis; in the Lower Mainland of BC the tick vector is Ixodes pacificus. Here in the Central Interior, it is believed to be too dry for I. pacificus and from my limited research I have not found any I. scapularis. I did find two stages (nymph and adults) of Ixodes angustus. However, three stages are needed to prove a resident population: larvae, nymph, and adult. The West coast and Point Peele National Park in Ontario are accepted as the most infected areas at present; which describes the path of the major migratory flyways. However, the disease is being found beyond the flight paths, many birds are deviating from their usual migratory routes, as evidenced by the numbers of rare bird sightings. It also means that exotic species of Ixodes ticks from South America are being found in unlikely locations.

To further compound the problem, we nature lovers inadvertently invite reservoirs of infection close to our homes by providing bird habitat complete with bird-baths and feeders, and supplying food to squirrels and chipmunks. Thus, we increase the potential odds of being infected via a tick that has fallen from birds or animals.

The mechanical transmission of Lyme Disease is considered controversial by some but it does explain how Lyme Disease may be contracted in an area that has a reservoir of infection and biting insects. If a biting insect is disturbed while feeding on an infected animal or bird, it may decide to finish feeding on you. It may have spirochetes (Lyme infection) on its mouth parts or feeding tube (dirty needle). There may be spirochetes in the blood it has ingested, when you smack it, this may cause it to regurgitate disease into the bite site.

With special thanks to Dr. Willy Burgdorfer (now retired) for the time he spent in helping me to understand the concept of the mechanical transmission of Lyme disease. Mr. Burgdorfer made it very clear that this has never been scientifically proven and will be hard to do so. If a large reservoir of infection is found here in the Central Interior this concept could be very important in that a large portion of the population is rural.

The bushy-tailed wood rat has been found to be a competent reservoir of Lyme Disease in California. This is our common pack rat.

When I became ill in l985, I was in an area that did not have a deer population to support ticks. But there were moose and rabbits; and it is the latter I will focus on as I feel this is where my disease originated. Rabbit populations crash, roughly every ten years, and it is during these "crashes" that rabbit ticks may indirectly become a threat to man as ticks need a blood meal to propagate.

Rabbit ticks do not often bite humans, but they do attach to birds and mice, possibly infecting their hosts and hard-shell ticks that may feed later. For example, if a rabbit tick is infected and gets its' next blood meal from a mouse; that mouse may also become infected. If an Ixodes angustus tick also feeds on the mouse, there is a chance of infection to man. Ticks wait patiently near a pathway or trail used by animals or man, attracted by the minute amounts of carbon dioxide given off by them.

Lyme Disease maintains itself in nature through these cycles of infection. But there is a further cycle of infection possible that has not been well studied. Log homes are frequently near rabbit populations, mice often make their way indoors in the summertime. In your house you may have vectors of Lyme Disease that you are not aware of. Lice, soft-bodied ticks, and even bed bugs may play a role in the transmission of Lyme Disease to you. There are many species of soft-bodied ticks, including O. hermsi. It is speculated that O. hermsi is responsible for my illness. O. hermsi can feed and transmit disease in minutes, compared to hours necessary for hard-bodied ticks. O. hermsi can survive long periods of not feeding.

Local trappers tell me that a rabbit die-off is about to occur. When the rabbit tick loses its' natural host it may find the next most abundant host, the mouse or a ground-foraging bird. When I became ill, mouse populations were at their high cycle. It is at this time every effort should be made to keep mice out of homes, and discouraging them wherever possible. After the die-off, the rabbits will rebuild their populations, thus reducing the possibility of infecting man. It is the ticks that attach to birds that require further study; where will they go and what will they infect?

After the die-off hare populations should be monitored to ensure they rebuild normally. If a contagious disease were introduced to a rebuilding population the hares may be decimated, putting humans at risk.