Life After Lyme Disease

Tiny adult tick

Domestic animals are prone to a number of insect-borne diseases including Lyme disease, and recent figures show that nearly as many as 30% of all canines in high risk areas will have been exposed to the bacteria which causes Lyme disease, Borellia burgdorferi.  Lyme disease can be a difficult condition to diagnose and treat as many people are not aware of this condition and how it can affect their pets, and after infection the majority of canine patients are never fully cured of the bacteria, despite receiving treatment.  The severity of Lyme disease can vary from mild but persistent symptoms of fatigue and joint pains through to more serious forms of the disease which can cause fatal health breakdowns such as kidney failure.

Prevention

When it comes to Lyme disease in domestic animals prevention is the key, and this means that pet owners will need to understand about the life cycle of ticks, so that they can put effective tick control methods in place.  Ticks follow an annual lifecycle and are not harmful to pets and in all of their development stages.  During the summer ticks are generally in the immature stage and by late summer they actually stop feeding and enter the pupation stage so at this point there is a lower risk of infection, but many pet owners mistakenly believe the summer months are key times to protect against ticks.  In reality the most important stage of the tick’s development occurs in around February to March time, when the adult stage peaks and the ticks begin to feed voraciously in preparation for breeding in early spring.  This is the key time of year when ticks present a high risk of carrying the Lyme bacteria over to pets, and owners should begin using tick control methods when the adults emerge in late fall, and continue right through to early summer.

It is also important that pet owners use the right tick control methods, and for those living in high risk areas it is best to stick to veterinary-quality products as these offer a much higher level of effectiveness against ticks (90% or above) than the equivalent over-the-counter versions, so although this will cost more and will have to be sourced from your vet you will be able to provide more protection for your pet against Lyme disease. 

Adult tick feeding on a dog

Diagnosis

One of the problems with diagnosing Lyme disease is that ticks are very tiny, even in the adult stages, and so it can be difficult to tell whether your pet has been bitten or not.  If you live in a high risk area for ticks and your pet is regularly exposed to thick vegetation, wild areas and woodland edges then the likelihood of them being bitten is very high, so if your pet displays any unusual symptoms it is worth asking your vet about the possibility of Lyme disease.

Lyme Vaccinations for Pets

Bacterial vaccinations have evolved in recent years but there is still of lot of hesitancy from both vets and pet owners in using these methods to prevent against insect-borne conditions such as Lyme disease.  This is because there is a lot of misinformation about how effective these vaccinations can be, but recent studies have shown the new vaccine technologies can provide safe, effective ways to reduce the risks of pets contracting Lyme disease.

Insects that feed on animals are primary carriers of a number of unpleasant diseases, and many of these can be transmitted from animals to humans such as Lyme disease, which is caused by the bacteria Borrelia burgdorferi.

Humans have a significant impact on fragile ecosystems all around the world, and research suggests that increasing urbanization and modern forest management techniques can all have a significant impact on the spread of tick-borne disease.  We often think of dramatic environmental disruptions happening in far away places such as the rainforests or Arctic glaciers, but similar problems are occurring with ecosystems right in our own backyards, and this can result in a number of problems such as an increased risk of exposure to infected ticks carrying the bacteria which causes Lyme disease.

Urbanization spreading into wild areas

Urbanization

Ticks mostly feed on woodland mammals such as mice, rabbits and deer, and because their chosen prey is more abundant at woodland and forest edges this is also where the population densities of ticks are the most concentrated.  Spreading urbanization has put woodland and forests under threat and pushed the boundaries between residential and wild areas even closer, and this means that there are more and more people living and working in high risk areas for Lyme disease.

Forest Management

Both ticks and their prey need certain habitats in order to survive, and researchers at the Washington University’s Tyson Research Center discovered that in the Missouri Ozarks (predominantly oak and other hardwood forests) those areas which were managed by the Missouri Department of Conservation and the Nature Conservancy were actually more at risk from tick-borne diseases crossing to humans and domestic animals, as selective logging and managed burns of the woodland created much more sustainable habitats for the prey ticks fed from, in particular deer and small mammals such as rabbits which both prefer the tender fresh green growth that is abundant in newly cleared woodland areas.

Woodland management can create ideal habitats for ticks

Researchers were keen to determine exactly which species were the main feeders of infected ticks in a typical woodland enviroment, and so collected ticks from a variety of sites in the managed woodland and wilder areas, and analyzed the DNA in the blood the ticks had fed on to identify which animal the blood came from, and whether or not any pathogenic bacteria were present.  This research provided some interesting results and it was found that stable deer populations did not significantly effect the spread of tick-borne diseases, but that concentrated populations brought about by plentiful food and protected habitats caused a dramatic increase in the impact and spread of tick-borne diseases such as Lyme disease.

The Importance of Tracking Emerging Diseases

With Lyme disease and other insect-borne diseases it is important we fully understand under what conditions the carriers of these pathogens can multiply and spread, as this will help health authorities and governments to identify and track emerging patterns of these potentially harmful diseases and put measures in place quickly to minimize the impact on humans.  For example the research from the Ozarks showed that managed environments caused explosions in deer populations, which in turn led to the increased risk of Lyme disease passing to humans and other animals, and this could be a significant piece of evidence to drive measures against the spread of ticks in the future, particularly when you consider that some state agencies actually encourage deer populations by planting out food for them.  In Missouri alone it was estimated that there were over 1.4 million deer, and this seems to be a similar pattern in woodland across the US, and researchers have estimated that there could be as many as 30 million deer currently living wild in the the mid and eastern United States.  It is likely that alongside these increasing deer and rabbit populations levels of other small mammals such as squirrels, shrews and mice are also booming, which can also be key prey sources for ticks, and all of this could explain why tick-borne diseases are spreading despite many efforts to hold them in check.

White footed mouse - Peromyscus leucopus

The Borrelia burgdorferi bacterium responsible for Lyme disease can infect humans, birds and mammals, and is transmitted to different hosts by tick bites. There are a number of animals that can carry the Borrelia burgdorferi bacterium and they can pass this on to uninfected ticks, but in many cases of zoonotic diseases (those transmitted from wild animals to domestic animals and humans) there is one natural animal host in particular responsible for incubating the bacterium. In the case of Lyme Disease researchers had historically considered mice (in particular white-footed mice) to be the main animal reservoir for this disease in North America, as past studies have shown that almost 90% of all ticks feeding on infected mice pick up the Borrelia burgdorferi bacterium, which is an infection rate almost double of any other species. Also mice are very common animals that occupy diverse habitats from woodland to residential districts, which would increase the spread of this disease across a larger area and this combined with the high infection rate would support the assumption that mice were the primary reservoir of Lyme disease.  Current vaccination strategies aimed at bringing Lyme disease under control throughout northern America have been based on the assumption that white footed mice are the main source of the Borrelia burgdorferi infection cycle.

New Studies

However new evidence from studies undertaken by biologists from the University of Pennsylvania have revealed that Lyme disease may have a much more complicated host pattern than first thought, and that there are actually a wide number of vertebrate species that contribute to transmitting the Borrelia burgdorferi bacterium. In a recent in-depth study carried out in the high risk tick infection area of the Hudson Valley, researchers discovered that both mice and deer (another species that is commonly linked to Lyme disease), did not actually factor very highly in the cycle of transmitting the Borrelia burgdorferi bacterium infection. The research revealed that just 25% of infected ticks were fed by mice, much less than the 55% of infected ticks discovered to have been fed by shrews in the same area. This evidence indicates that other factors such as animal population density had a huge influence on the spread of the Borrelia burgdorferi bacterium, and that focusing on just one species such as the white-footed mouse was not an effective way to combat the spread of this disease.

Combating Lyme Disease

Zoonotic pathogens (such as the Borrelia burgdorferi bacterium that causes Lyme disease) that can cross easily between human and animal species are a major threat to ecological systems all around the world, and areas where residential and wild land converge such as at forest and woodland boundaries are particular high risk zones. It is very important that researchers understand exactly how the diseases spread to

Woodland edges are high risk areas for Lyme Disease

different species and across to humans, so that they can work with governments and health authorities in finding new strategies to help protect the public and minimize the spread of infection both in wild and domestic animals. Identifying the main animal host or hosts of pathogens such as Lyme disease can be a key weapon in combating the impact of zoonotic emergences, as strategies can be implemented that interrupt the transmission of infection such as between the ticks and the primary animal hosts, thereby breaking the infection cycle and preventing the disease from spreading to new areas.

An Ixodia tick is a very small tick which is much smaller than dog or cat ticks. The juvenile deer tick is about the size of a pinhead, the biggest adult deer tick can grow to about three-sixteenths of an inch.

A Lyme disease infection can happen after a deer tick is attached to a human or other host for twelve to twenty-four hours. An infected deer tick has Borrelia that lives in the tick’s midgut. Ticks are parasites that insert their mouthparts into their hots and drink blood for several days. When an infected tick attaches itself to a host and feeds, the Borrelia enters the salivary gland and proceeds into it”s human hosts blood stream.

The tick larvae and nymphs usually become infected with Borrelia burgdorferi when they feed on infected small animals, in particular the white-footed mouse. The bacteria remain in the tick as it changes from larva to nymph or from nymph to adult. Infected nymphs and adult deer ticks then start feeding on other small rodents, other animals, and humans, and transmit the bacteria to them. Adult ticks preferentially feed on the white-tailed deer, which thereby becomes an significant source of Borrelia burgdorferi in regions of infestation. The tick’s life cycle takes two years to complete (see diagram below).

The deer tick’s life cycle is comprised of three distinguishing stages: larvae, nymphs, and adults and lasts aproxinately two years.

In the spring and summer of the first year, eggs hatch into larvae which feed once and molt into nymphs. Nymphs become dormant for the fall and winter.

In the second year, nymphs emerge to feed from May through July. At this time, the nymph may transmit bacteria to humans or to wild or domestic mammals.

In the fall, nymphs molt into adult ticks. The females feed on deer and various large mammals, mate, lay their eggs, and then die. If females don’t feed in the fall, they will try to find a large mammal host during the following spring. Male deer ticks attach to a host to wait for females, but do not take a blood meal.