Lyme Disease: Cause, Transmission, and Geography of Concern
Lyme disease is caused by bacteria of the genus Borrelia transmitted by the bite of a tick of the genus Ixodes. the is transmitted by ticks infected with various diseases in both Europe and North America. Both places are affected by a similar species of genus of bacteria. It is a spirochete belonging to B. burgdorferi sensu stricto are primarily found in America while in Europe it is Ixodes ricinus. the time needed to transmit the disease is usually within 12 hours of attachment. This is why it is so important to remove ticks as soon as found and to treat our pets with flea and tick preventative (Sertour, 2018).
Lyme disease is one of the most commonly reported vector-borne diseases in the US. The disease was first identified in 1975 in the town of Old Lyme, CT and was therefore named Lyme disease. It is caused by the bacterium Borrelia burgdorferi sensu stricto. Through Ixodid species tick bites pass this bacterium to humans. Early symptoms of Lyme disease include skin rash, fever, headache, and fatigue. If the patients are not treated during this stage severe and chronic symptoms can occur.
Chronic symptoms include arthritis in major joints, shooting pains, numbness in hands and/or feet, and memory issues. Although New England and other northeastern states are the initial endemic area for the disease, it has since expanded over the last several decades to include Virginia as its southward front line. Because transmission of Lyme involves tick bites, which are related to both environmental and human factors, this study looks at demographic factors that can contribute to the emergence of the disease.
In past studies of white-footed mice and deer are shown to be a very important host of ticks. Forested and herbaceous/scrub areas are ideal habitats for the mice and deer. Scrub can be tall enough to provide concealment for the dear and still have enough shade and humidity to allow black-legged ticks to survive the hot dry months of the summer. The percentage of the herbaceous cover has positive relationships with Lyme disease counts which are consistent with the findings of other studies. They also made use of a five-year study in order to study the overall environmental and economic variables on the Lyme disease occurrence (Xie, 2018).
Lyme disease (LD) is a bacterial infection transmitted by the black-legged tick (Ixodes scapularis) in eastern North America. It is an emerging disease in Canada due to the expanding range of its tick vector. This study found that passive surveillance helped local-scale environmental risk for the tick vector LD at sites of interest in public health. The actual organism that causes LD is a spirochete B.burgdorferi and transmitted by black-legged tick risk maps using this studies results should be interpreted cautiously because actual tick presence may differ from predicted values for a variety of reasons.
They also found there is a low baseline risk of tick encounter anywhere that ticks can be dispersed by their hosts like birds and deer. The study also raised concern about the future risk of LD. Since warming temperatures have rendered the area broadly suitable from a climatic perspective and suitable habitat exists surrounding populated areas (Soucy, 2018).
The emergence of vector-borne diseases in a new region creates a pressing need to understanding underlying their rapidly changing distribution. Vector distribution is crucial information for vector-borne disease management, often providing the main source of data used to assess the epidemiological situation and the risk of transmission to humans. There is a gap found in this study between the potential distribution based on suitable environmental conditions and the realized distribution.
About 30,000 cases of Lyme disease were reported in 2016 in the US. Human risk of exposure to B. burgdorferi distribution is of I. scapularis. This distribution is closely linked to the I. scapularis population. Under appropriate climate conditions, I. scapularis prefers to live in deciduous woodlands such as mature oak and maple forests. In the area covered by this study, 86% of I. scapularis was found in 2014. Of this 13 %, nymphs and adults were infected by B. burgdorferi. This study provided evidence that tick distribution is not uniform at multiple scales within a newly invaded region.
This study could help the public to better understand the local risk to which they are exposed and to adopt proper behavior to limit their exposure. Hunters and hikers are cautioned to be vigilant in taking measures to reduce tick exposure. This can be done by using insect repellents, tight leggings to reduce the opportunity of tick hitching a ride and once home again careful inspection of all surfaces of the body to catch them before they have a chance to bite. This includes flea & tick repellent on pets to reduce the chance of them being brought into the home via one of the animals (Ripoche, 2018).
Over the past decade, since the first American College of Veterinary Internal Medicine (ACVIM), small animal Lyme consensus statement was written a broader understanding of strains of B. burgdorferi sensu strict (Bb) and the diversity of other pathogens carried by Ixodes and other ticks has been gained. Geographic distribution of infected ticks has expanded because of bird migration and suburban sprawl. And diagnostic tests are now available to help rule out co-infections and other causes of clinical signs that point to a possible Lyme borreliosis (LB). This study has found most cats and dogs show no clinical signs of illness even though they have tested positive. The Ixodes vector feeds on a variety of hosts.
Within endemic geographical areas, the prevalence of Bb in adult ticks can reach 50%. In addition, most Bb infections occur in the warmer months impacting the recreational habits of humans and their canine friends. Adult Ixodes ticks can be active in fall, winter, and early spring. Deer are important to these ticks as adult ticks mate on them. It has been noted that decreases in vegetation and reservoir hosts, including deer, will result in a gradual decrease in disease.
There is a strong consensus that tick control must be used not only to help prevent LB but also other TBD in Bb-endemic areas for which there was no vaccine available. Because adult ticks are active even in winter, year-round preventative is suggested for pets. There are many products available both topical and oral that have on their label they are effective against I. scapularis. And while this study doesn’t endorse any specific product, they do recommend the use of a product that quickly kills or prevents attachment and feeding by the tick (Littman, 2018).
Littman, M. P. et al. (2018). ACVIM consensus update on Lyme borreliosis in dogs and cats. Journal of Veterinary Internal Medicine. American College of Veterinary Internal Medicine. Doi:10.1111/jvim.15085
Ripoche, M. et al. (2018). Multi-scale clustering of Lyme disease risk at the expanding leading edge of range of Ixodes scapularis in Canada. International Journal of Environmental Research and Public Health,15(4). https://doi.org/ijerph15040603
Sertour, N. et al. (2018). Lyme disease: A study on the speed of transmission by infected ticks. Institut Pasteur Research Journal. https://www.pasteur.fr
Soucy, J-P. R. et al. (2018). High-resolution ecological niche modeling of Ixodes Scapularis ticks based on passive surveillance data at the Northern frontier of Lyme disease emergence in North America. Vector-Borne and Zoonotic Diseases,18 (5). Doi:10.1089/vbz.2017.2234
Xie, Y. et al. (2018). Spatial variable selection and an application to Virginia Lyme disease emergence. Cornell University Library. https://arxiv.org/abs/1809.06418