Pathogenesis, Prevention and Control of Lyme Disease in Public Health

Introduction

Lyme disease is a zoonotic disease and was first recognised in 1975 in Connecticut, U.S., by Dr. Burgdofer (Discovery of the disease agent causing Lyme disease, 2018). The disease is transmitted from bacteria to vertebrae animals, including dogs, horses, birds, livestock and humans, through the bite of an infected tick.

What is Lyme disease?

Lyme disease, also known as Lyme Borreliosis, is caused by a gram-negative spirochete Borrelia burgdorferi, and is transmitted by black-legged ticks, belonging to the genus Ixodes (2014, pp.487-497). In canines, it causes fever, lethargy, lameness, swelling of the lymph nodes and red lesions around the bite for the first few weeks of infection. Lameness is more of a long-term symptom as it can occur for between 2 to 6 months post infection, (Straubinger, R.K., et al. 1997). Dogs that become infected with Lyme disease have a risk of developing Lyme nephritis, which could result in acute or chronic renal failure with vomiting, dehydration, anorexia, polyuria and polydipsia (Littman, M., et al. 2006).

Transmission of the disease

Ticks have three life cycles over two years, including larvae, nymphs and adult ticks (O’Connell, S. 1995). The ticks feed once during each life stage. Larvae tend to feed on field mice and voles, whereas adult ticks feed on larger mammals and birds, including sheep, deer and horses (O’Connell, S. 1995). Birds and mammals, particularly deer, rodents and birds, act as reservoirs of Ixodes spp. and maintain the tick population (Barbour, A.G., 1998). Infected birds and mammals have the ability to pass on the disease to adult ticks when they feed, contributing to the increase in infected ticks. It’s questioned that the growth of deer populations and the reforestation of farmland has contributed to the emergence of Lyme Disease (Barbour, A.G., 1998). In areas where Lyme Disease is less common, migratory birds could potentially introduce infected ticks and transmit the disease there.

Risk Factors

The area of inhabitation and travel is a major risk factor for contracting the disease. Lyme disease is highest in southern parts of the UK, including Bristol, and also is seasonal, occurring at higher rates during spring, summer and early autumn. For pet owners, exposed skin is a risk factor when their animal has been infected, as, although there is no direct transmission from dogs to humans, dogs can bring unfed, infected ticks into the house (2014, pp.487-497). Outdoor recreational activities in areas of woodland, pasture, heath and areas of dense vegetation increase the risk of infection, as well as areas with infected deer and mice populations (O’Connell, S., 1995).

People most at risk from the disease are forestry workers, deer managers, gamekeepers, farmers, soldiers, outdoor educators, conservationists ramblers and campers.

Advice on dealing with the disease

Dogs bringing in uninfected ticks into the house is a risk for owners. To prevent infection, owners must ensure any exposed skin is covered or that lighter clothing is worn to identify any ticks present. An insect repellent can be used to deter the ticks from attaching, DEET is applied to the skin and permethrin is used for clothes (Duncan, C., et al. 2012). When humans are infected, skin lesions known as erythema chronicum migrans develop (Burgdorfer, W., et al. 1982). The symptoms may progress to neurologic or cardiac abnormalities and different forms of arthritis, including polyarthritis, oligoarticular arthritis and chronic arthritis.

Dogs are treated for Lyme disease with antibiotics, commonly doxycycline. (2014, pp.487-497). Four weeks of treatment using this antibiotic is recommended (Littman, M., et al. 2006). Dogs suffering from polyarthritis usually respond to the antibiotics within 24 to 48 hours. Doxycycline is also recommended to dogs with Lyme nephritis but will require other treatments alongside the antibiotic (2014, pp.487-497). An alternative antibiotic to doxycycline to treat this disease is amoxicillin, as some dogs may be intolerant to doxycycline. The pain from arthritis can be treated with nonsteroidal, anti-inflammatory drugs or opiate analgesics, such as tramadol (2014, pp.487-497).

Prevention of the disease

Regularly checking for ticks on the skin of both the dog and the owner could avoid infection. Transmission of the disease can be prevented by removing the tick within 24 hours (2014, pp.487-497). Ticks must be removed in a certain way to avoid transmission by rupturing the tick; tweezers or tick removal devices should be used to gently pull them out, grabbing it as close to the skin as possible, without twisting it (Duncan, C., et al. 2012).

Another way of preventing the disease is to avoid tick-infested environments and to keep to the footpath. Sitting on logs or against trees, gathering wood and walking will increase the risk of infection as an owner, and also for their dog by walking in woodlands and pastures. Dogs can receive regular treatment to reduce the risk of infection, including spot-on applications, impregnated collars and sprays (Otranto, D., Wall, R., 2008). These provide protection against feeding ticks.

Vaccines against Lyme Disease

Borrelia burgdorferi expresses different outer-surface lipoproteins during different stages of infection (2014, pp.487-497). This advantageous trait allows the organism to adapt to the different environments in both the vector and the host. The bacteria express OspA, OspC and VlsE outer surface proteins, with each one playing a different role in how the spirochete evades the host (2014, pp.487-497). During the autumn and winter, the spirochete is dormant and expresses OspA, causing it to bind to the midgut of the tick. The bacteria up-regulates the expression of OspC surface protein and down-regulates the expression of OspA in spring and summer. During this time, the pathogen ingests the blood, and the change in gene expression causes itself to move to the tick salivary gland and, with the aid of a protein, can evade the host (2014, pp.487-497). Discovery of the change in surface protein expression has helped to create a vaccine for dogs.

A potential solution to Lyme disease is a vaccine. Vaccines should only be given in endemic areas, where the risk of Lyme disease is high. Through vaccination, borreliacidal antibodies are present in the dogs’ blood, which are specific to the surface proteins on the bacteria (2014, pp.487-497). When the tick ingests the blood, the antibodies bind to the surface proteins and causes complement-mediated lysis of the bacteria within the tick. The spirochete is inactivated before invading and infecting the dog (2014, pp.487-497). A recombinant OspA vaccine provides antibodies against the OspA surface protein only. Another vaccine consists of two inactivated spirochetes, with one containing two strains of B.burgdorferi, and the other containing only one strain. This provides immunity to other surface proteins, including OspC (2014, pp.487-497). The use of vaccines to prevent Lyme disease is controversial and is recommended to be given to dogs in high-risk areas only.

Actions taken by the authorities

Educating the public on ways to prevent the disease, how to identify the disease in their pets and increasing awareness is an important step in controlling Lyme disease. The National Institute for Health and Care Excellence (NICE) provides guidelines and information about the disease, and guidance on removing ticks are found on Public Health England’s (PHE) tick surveillance pages for the public to access (Cruickshank, M., O’Flynn, N., Faust, S., 2018).

There are many non-government organisations both globally and in the UK with the aim to explore the disease and educate the population (Organizations for Lyme Disease – Prohealth 2018). Global Lyme Alliance and International Lyme and Associated Diseases Society (ILADS) are both international organisations that promote educating the disease, including the basics of it and ways to prevent it, with ILADS also educating scientists, doctors, researchers and healthcare professionals. LymeAid is a UK charity providing support for people with Lyme disease (Kellaway, 2018). Lyme Disease Action (LDA), a UK based organisation, aims to increase Lyme awareness, write papers for medical journals, participate in the Tick Activity Project and organise speakers for the LDA September Conference (Lyme Disease Action What We Are Doing | Lyme Disease Action, 2018). Lyme Research UK is another UK organisation that researches into the disease.

To minimise the infection of Lyme disease, tick populations and animal-tick interactions must be reduced (Wilson, E., Smith, K., 2009). A practical way of achieving this is to modify the local habitat, by removing vegetation around buildings and clearing dense vegetation from public areas.

Deer population reduction has been suggested as a potential way to prevent Lyme disease and reduce the number of black-legged ticks (Kugeler, K., et al. 2015). However, there has been no sufficient evidence to prove that the reduction in deer populations will reduce Lyme disease. This prevention method is politically insensitive and brings in ethical dilemmas, adding to the problems of this idea. A more socially acceptable way of targeting deer populations is by providing feeding stations that make deer rub against 4 amitraz-impregnated posts which transfer acaracide onto their heads and necks, preventing tick attachment (Sonenshine D.E., et al. 1996). In the study, it was found that the areas without the feeding stations had more ticks than that observed in the area with the feeding stations.

Conclusion

Lyme disease can potentially have serious effects on the animal or human, yet can easily be prevented by taking small measures such as covering yourself, checking daily for ticks in your pets and avoiding woodland areas with dense vegetation. Lyme disease in dogs can easily be treated by antibiotics and the effect from this has been seen. Vaccines for the prevention of the disease in dogs is still quite a new advancement and there are controversial views on the use of them. The best method in reducing Lyme disease infection is to increase awareness of ways to prevent the disease and recognising the signs, which is promoted by organisations such as Lyme Disease Action and Global Lyme Alliance.

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