Ashley Sutton Term Paper - Lymes_Disease

Ashley SuttonVBSC 303HTerm PaperFall 2014

Lyme disease was first diagnosed in the early 1970’s after a group of children in Lyme,

Connecticut developed rheumatoid arthritis. It was determined early on that the condition came

from a tick bite; however it was not until 1981 that the actual cause was discovered. The

causative organism was found to be a spiral shaped bacteria or spirochete, that was named

Borrelia burgdorferi in honor of the scientist, Wilhelm “Willy” Burgdorfer, who helped to

discover it. The genospecies found in the United States is Borrelia burgdorferi sensu stricto,

which infects humans at a rate of thirty-thousand people per year. B. burgdorferi is spread by the

deer tick (black-legged tick) or Ixodes scapularis which acts as a mechanical vector. The Borrelia

organism lives in the tick’s GI tract and is transferred to animals during blood meals. Research

supported by the NIH and DCD suggest that a tick must be attached for a minimum of thirty-six

hours to transmit Lyme disease.

Stage one symptoms of Lyme disease often start with a distinctive rash known as

erythema migrans. This red circular rash typically develops a characteristic “bull’s eye”

appearance, since many people do not remember ever being bitten by a tick this is often the first

sign of infection. In state two one may develop more general symptoms that would be common

with many bacterial or viral infections such as fever, chills, fatigue, swollen lymph nodes, joint

pain (chronic Lyme arthritis), and a generalized rash. Stage three may involve intermittent

episodes of joint pain, meningitis, Bell’s palsy, or cardiac involvement.

The prevalence of Lyme disease is highest in the North-central and Northeast United

States. Pennsylvania consistently reports a higher number of Lyme disease cases to the CDC

than the national average and has a high concentration of cases in the Southeastern corner of the

state. Lyme disease infects humans, as well as dogs, horses and sometimes cattle. Mice,


chipmunks, gray squirrels, opossums, cottontail rabbits, and raccoons can also be infected and

are common wild animal reservoirs.

The pathogenesis of Lyme disease includes the extracellular invasion of blood and

tissues, with a mechanism that is unknown. (Baranton 1990) Normally the immune system

would recognize bacteria as foreign and mount an immune response, but B. burgdorferi has

several mechanisms to avoid detection. The spiral shape of B. burgdorferi, combined with its

movement in a corkscrew fashion, allows it to hide its antigenic flagella inside the spiral. It is

likely a combination of factors that allows B. burgdorferi to infect and cause disease. B.

burgdorferi lives near collagen and fibroblasts, typically not causing any inflammatory response.

Noninfectious strains of B. burgdorferi have mutations in, show reduced expression, or lack

(outer surface protein) OspB, OspD, OspC, or vls genes in particular. They also have lost several

plasmids, including linear plasmid 25, 28.4 and circular plasmid 9. It is likely that the diversity

of the host immune response also has an effect on the outcome of exposure to B. burgdorferi.

(Thomas 2001)

In humans the most obvious clinical sign of Lyme disease is erythema migrans, which is

caused by a severe inflammatory response. The inflammatory response is initiated by the

lipoproteins on the surface of B. burgdorferi which activate pro-inflammatory products in many

cells including macrophages, endothelial cells, neutrophils, and β lymphocytes. The activation of

these cells causes the release of pro-inflammatory cytokines and chemokines.

In a mouse model of innate immunity, those deficient in toll-like receptors showed an

increased inflammation which was ineffective at clearing the organisms, having bacterial loads

in the joints one to two times higher than in wild-type mice. The adaptive immune response also


has a significant role in B. burgdorferi infection. B cells are important in the control of pathogen

burden and resolution of arthritis while T cells are required for inflammation but not controlling

the pathogen burden. In mouse models where SCID (severe combined immunodeficiency

syndrome) mice, which lack B and T cells, were infected, the mice had higher pathogen levels,

but a similar severity of arthritis.T cells, macrophages, dendritic cells, and neutrophils have been

found in biopsies of erythema migrans lesions. T cells are directly involved in the development

of arthritis and carditis, but do not play an important role in the resolution of the disease. The

ratio of Th1 cells to Th2 cells in synovial fluids correlates with the severity of arthritis, with

higher Th1 cells indicative of more severe arthritis. Natural killer cells can recognize B.

burgdorferi and prevent joint inflammation and disease clearance. (Shin 2014)

Persistent infection happens with an unknown mechanism. Some suggested mechanisms

are that B. burgdorferi binds to various compounds of the extracellular matrix to avoid the

immune response. Another documented occurrence is the changing of surface antigens which is

thought to help the pathogen evade detection. Lastly B. burgdorferi might induce an autoimmune

response which produces a chronic infection. (Shin 2014)

Infection of horses with B. burgdorferi is common; however the extent of clinical disease

is questionable because most horses show few clinical signs. (Bartol 2013) In horses the clinical

disease is termed Lyme borreliosis, it includes symptoms of arthritis, uveitis, lameness, and

sometimes encephalitis. Uncommonly an infection with B. burgdorferi may manifest itself as

Lyme neuroborreliosis, which may be mistaken for equine protozoal myeloencephalitis (EPM).

Nervous signs including pain, muscle atrophy, and hyperesthesia; eventually it can progress to a


disease that requires euthanasia. The most significant findings are found in the central nervous

system from the rostral cerebrum to the thoracolumbar spinal cord. (Imai 2011)

In order to be transmitted, the B. burgdorferi organism must change the expression of its

outer surface proteins to evade the immune system of its host. Outer surface protein A must be

downregulated, while Osp C and Osp F must be upregulated. (Bartol 2013)

In dogs, most exposed remain clinically normal. If symptoms develop the dog will

become ill, have arthritis, fever, anorexia, and lymphadenopathy. Since dogs are more likely to

be exposed to humans, the number of infected dogs is a good indicator of risk to the human

population in a given area. The most serious form of Lyme disease in dogs is called Lyme

nephritis. Lyme nephritis is caused by immune-mediated glomerulonephritis with Lyme-specific

antigen-antibody complex deposition. (Littman 2013)

When it comes to animals in the wild, most show no signs of disease if infected with B.

burgdorferi. At least fifty-three species of wild mammals and birds have shown to be naturally

infected with B. burgdorferi. Infection of ticks from wild animals can happen in any of its three

life stages. The tick vectors typically feed once as a larvae once as a nymph and lastly once as an

adult female. Transmission of B. burgdorferi to ticks occurs while feeding on one of the infected

hosts. It does not occur transovarially (transmission from the female to her offspring) and the

infection persists through the molt into the next life stage of the tick. (Brown 2008)

Lyme borreliosis is the most prevalent vector-borne human disease in both Europe and

the United States. The disease is most common in children aged five to fourteen and adults aged

thirty to fifty-five. The epidemiology is related to the interactions of B. burgdorferi, its vectors,

and hosts, as well as the habitats they inhabit. Since each life stage only feeds once, adult ticks


do not contribute significantly to the reservoir of B. burgdorferi, and immature ticks are the key

to the transmission cycle. In certain habitats, some lizards and deer are important hosts for vector

ticks, but they do not serve as significant reservoirs of B. burgdorferi. (Brown 2008)

The prevalence of equine Lyme disease is similar to that of dogs. Areas in the

northeastern and mid-Atlantic region, as well as a part of the Midwest, are affected. One New

England survey reported forty-five percent of horses had antibodies against B. burgdorferi, and

in Wisconsin one-hundred eighteen of one-hundred ninety horses tested positive. (Divers 2013)

There are several detection methods used in different species. In all species, culture of the

spirochete remains the gold standard for detecting infection. It is not commonly used however

due to being labor and time intensive and relatively expensive. PCR is another method that may

be used, however it has a high probability of contamination so it is only available at select

research institutions and diagnostic labs. Serology is currently the best method for detection of

Lyme Disease. ELISA tests are the most sensitive tests in humans, with immunoblotting used as

a secondary confirmatory test. (Brown 2008)

In dogs, SNAP tests from IDEXX tests for heartworm antigen as well as antibodies

against Lyme C6 peptide, Anaplasmosis, Ehrlichia and other common illnesses. C6 is a

recombinant protein that mimics the sixth conserved invariable region of the VlsE family, and

antibodies against it are sensitive and specific to a natural exposure as opposed to a vaccine

exposure. The Multiplex test from Cornell University includes a Western blot, and quantitative

tests for antibodies against OspA, OspC, and OspE. This is relevant because OspA antibody is

seen in a vaccine reaction, OspC is related to a recent infection and OspE is related to a

persistent infection. (Bartol 2013) The last type of test commonly used is the AccuPlex4 test by


Antech Diagnostics, which tests for heartworm, Lyme, Anaplasmosis, and Ehrlichiosis. It is said

to show infection one to two weeks earlier than other tests, even before signs of infection occur.

It uses an algorithm comparing five markers that differentiate vaccine and natural exposure

antibodies, and may also differentiate early and late infection. (Littman 2013)

In horses, the canine SNAP test is often used even though it has not been validated in

horses, although in one test it has shown to be sixty-three percent sensitivity and one-hundred

percent specificity in horses. The current recommendation is to use the snap test and follow up

any positive results with a Multiplex test. The equine multiplex test is a fluorescent bead

antibody test that detects and quantifies OspA, OspC, and OspF to give similar information to

the Multiplex test for dogs. (Bartol 2013)

One prevention method is vaccination. A vaccine has been developed for use in humans,

based on the immunogenic outer surface protein A. This is a good choice because it is

upregulated once B. burgdorferi enters the tick, and there is minimal heterogeneity in this protein

in the United States. The antibodies generated against OspA eliminate B. burgdorferi from the

tick during feeding which prevent them from entering the host. A vaccine is useful because

asymptomatic early infections are common, and prevent the effects of late term infections.

A product called LYMErixTM was licensed in 1998 by the FDA for use in fifteen to

seventy-year-olds. Antibody titers were proven to be comparable when vaccinated at zero, one,

two and zero, one, twelve months. Vaccination should occur several weeks before tick season to

offer protection. Suggested boosters would be twelve months after the third vaccine and every

two years after the fourth. The vaccine was shown to have great safety with about one million

vaccinations given and no patterns of adverse effects. A previous history of Lyme disease did not


affect the tolerability. (Poland 2001) Despite the positives of this vaccine, the costs of

vaccination are more than the cost of the averted disease, so the vaccine was taken off the market

in February 2002.

One of the main faults of the vaccine is it leaves those most at risk, children, vulnerable.

Children are especially vulnerable because not only are they in a high-risk age group, but only

fifty percent of children infected develop erythema migrans which would allow for early

diagnosis. Also, the main drug prescribed, tetracycline, is contraindicated in children, limiting

treatment options. The vaccination was being investigated for safety and efficacy in children,

which never manifested before the vaccine was pulled from the market.

Vaccination of dogs is common in endemic areas. Vaccines are available that contain a

recombinant OspA. Vaccines are given yearly with a booster dose one month after the first dose

is given. This vaccine is also used in horses although adverse effects, efficacy and duration of

protection are unknown. In one study the canine vaccine delivered to horses showed a significant

decline after 5 months post vaccination. The most common group of horses vaccinated is high-

level sport horses since these are the most common affected.

Oral vaccination of wildlife can be delivered via bait. The best approach to controlling a

vector-borne disease is to control the vector, however current methods using organochloride

pesticides produce unacceptable environmental effects. In the past, oral bait immunization has

been successful in treating the plague and rabies. OspA vaccination was tested via bait

administration and oral gavage in mice, with both being able to produce protective antibody

levels. Administration via bait however required a much higher level of antigen to produce the

same level of resultant antibody. The mice were then exposed to multiple B. burgdorferi strains


with tick challenge. There was zero percent protection in the control group, and 8 out of 9 were

protected in the vaccinated group showing an overall eighty-nine percent efficacy. In this study,

they also tested ticks for B. burgdorferi before and after feeding on the vaccinated mice. Before

feeding on the mice, there was an eighty-five percent prevalence rate, and after feeding the

infection rate was reduced to ten percent. This showed that the oral vaccine cleared a variety of

strains of B. burgdorferi from nymphal ticks. The raised levels of antibody lasted for about two

and a half months, which is longer than the larval host-seeking period of two months. After a few

years of bait delivered vaccination, the mouse-tick transmission cycle could be broken. (Gomes-

Solecki 2006)

Another method of preventing Lyme disease is preventing exposure to ticks. This can be

done by several methods, all of which require public education on the methods. When going into

areas where infected ticks could be found, one should wear long pants and long sleeves to

prevent skin exposure. Walking down the center of the trail and wearing light clothing can

prevent tick exposure as well as make them easier to find. Pants can be tucked into socks and

boots, and DEET can be applied to clothing and skin to prevent tick bites. Since transmission of

the spirochete takes approximately thirty-six hours, personal checks for ticks after being in

infected areas can prevent transmission. (Brown 2008)

Prevention in pets is similar to humans. Pets should be checked regularly for ticks,

especially if their environments bring them into close contact with ticks. Keeping the amount of

leaf litter reduced and making sure lawns and pastures are properly managed will also decrease

the exposure to ticks as well.


In conclusion, Lyme disease is an endemic disease in the United States which makes it a

topic of interest for the general public, as well as scientific minds. Much research has been done;

we have now developed the ability to produce vaccines for our pets and humans. We know how

to use serological tests to determine not only if infection has occurred, but to tell how long it has

been going on and if the antibodies are due to vaccination. We also have a lot of information

about new prevention methods focusing on reducing B. burgdorferi in wildlife populations. With

all these things considered, I believe there will soon be a day when the prevalence of Lyme

disease will be on a decreasing trend, instead of an increasing one.


Works Cited

1. Baranton, G. Lyme Borreliosis. 13 Vol. ENGLAND: Elsevier Ltd, 1990.

2. Thomas, Venetta, et al. "Dissociation of Infectivity and Pathogenicity inBorrelia

Burgdorferi." Infection and immunity 69.5 (2001): 3507.

3. Shin, Ok Sarah "Insight into the Pathogenesis of Lyme Disease". Journal of bacteriology

and virology 44.1 (2014): 1598-2467

4. Bartol, J. "Is Lyme Disease Overdiagnosed in Horses?" Equine veterinary journal 45.5

(2013): 529-30.

5. Imai, D. M., et al. "Lyme Neuroborreliosis in 2 Horses." Veterinary pathology 48.6

(2011): 1151-7.

6. Littman, Meryl P. "Lyme Nephritis." Journal of veterinary emergency and critical care

(San Antonio, Tex.: 2001) 23.2 (2013): 163-73.

7. Brown, Richard N., Williams, Elizabeth S. Infectious Diseases of Wild Mammals.

Ames: Iowa State University Press, 2001: 435-48.

8. Divers, Thomas J. "Equine Lyme Disease." Journal of Equine Veterinary Science 33.7

(2013): 488.

9. Poland, Gregory A., and Robert M. Jacobson. "The Prevention of Lyme Disease with

Vaccine." Vaccine 19.17 (2001): 2303-8.

10. Gomes-Solecki, Maria J. C., Dustin R. Brisson, and Raymond J. Dattwyler. "Oral

Vaccine that Breaks the Transmission Cycle of the Lyme Disease Spirochete can be

Delivered Via Bait." Vaccine 24.20 (2006): 4440-9.

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Ashley Sutton Term Paper - Lymes_Disease