NS05-Lyme Disease

Thomson

what is the causative agent of lyme disease?

Borrelia burgdorferi in the US

what are the physical traits of the bacterium?

morphology: spirochete - spiral-shaped bacteria

gram stain: gram negative

how is lyme disease transmitted?

transmitted via a vector

Transmission of Lyme Disease

tick-borne (vector-borne) disease → transmitted from animal reservoirs to humans by ticks

vector: transmission in US is black-legged tick, Ixodes scapularis. 

Infectious forms: larval and nymph stages of tick are capable of transmission. Nymph stage causes >90% of human cases because nymphs are smaller and harder to detect

Mechanism of Transmission

Borrelia burgdorfei grows in midgut of unfed tick

feeding induces migration of bacteria to salivary glands in tick

usually takes about 24 hours of feeding for transmission of Borrelia to occur

Zoonosis

humans are an accidental host

Most common animal host (primary reservoir)

small mammals, particularly white-footed mice, and also white-tailed deer

• mouse host is more relevant to human disease

• larval and nymph forms of the tick, which are most likely to infect humans, feed on and infect mice

• larvae laid by female ticks in the spring become infected by feeding on mice

• adult ticks usually feed on deer

Stage 1: Early Localized Stage

occurs 3-30 days after tick bite (avg incubation period of 7 days)

Symptoms of Stage 1

Erythema Migrans (EM) Rash: characteristic bulls-eye rash that develops at site of tick bite

• seen in 70-80% of patients

• rash starts at tick bite site and expands over several days, reaching up to 12 inchs or more

• rash is often erythematous with central clearing

• generally not itchy or painful (denies pain or pruritis)

• rash develops from immune response to the bacteria’s LPS

Flu-like symptoms:

• headache

• fever

• muscle pains (myalgias)

• malaise and severe fatigue

• enlarged lymph nodes near tick bite

Stage II: Early Disseminated Stage

occurs 2-10 weeks after the first signs and symptoms and can last days to months

bacteria spread through the blood to the brain, nerves, joints, and heart

Symptoms of Stage II

fatigue, headache, fever, malaise, and additional rashes

Neurological symptoms: occurring in 10-20% of untreated patients. These can include:

• facial nerve paralysis/palsy (Bell Palsy): which is caused by swelling pinching facial nerve, making it hard to smile or close eyes

• severe headache, peripheral nerve neuropathy, difficulty concentrating, meningitis

Cardiac symptoms: affecting 1-5% of pts, these symptoms arise as bacteria enter heart tissues and interfere with electrical conduction:

• cardiac dysfunction, atriventricular conduction block, myopericarditis, congestive heart failure

• may require pace-maker and can be fatal

Stage III: Late Persistent Stage

chronic stage begins approximately 6 mo or years after initial skin rash/symptoms

symptoms of Stage III

chronic arthritis: stage is characterized by arthritis, including joint pain and swelling

• involve one or many joints

• large joints are generally involved, particularly the knees

• caused by immune response to bacterial antigens, potentially resulting from autoimmune response against tissues

chronic nervous system impairment: include localized pain, paralysis, and depression

chronic skin condition: acrodermatitis chronica atrophicans may occur

Post-Treatment Lyme Disease Syndrome (PTLDS)

condition affecting some patients after antibiotic treatment

symptoms: pts many experience pain, fatigue, or difficulty thinking that lasts for more than 6 mo after they finish treatment

also known as Chronic Lyme Disease

what are some preventative measures to prevent infection

avoidance of ticks and their natural habitats. Key measures include:

• avoidance and awareness

  • know where to expect ticks (grassy, bushy, wooded areas)

  • walk in center of trails

  • ticks are most active during warmer months, though they can occur year-round

• protective clothing: wear long pants tucked into socks

• repellents: use of insect repellents

• post-exposure checks:

  • check for ticks when returning home

  • examine gear and pets

  • shower soon after being outdoors

  • check your clothing and body

Vaccines for Lyme Disease

recombinant vaccine was available: withdrawn from market in 2002

VLA15: currently undergoing Phase 3 study

Treatments for Lyme Disease

Generally, antibiotics given early can prevent late-stage manifestations

typical 2-4 week oral antibiotic course cures in most cases

Stage I → EM rash: oral antibiotics → usually doxycycline or amoxicillin for 2 weeks, lessens late manifestations but arthritis may occur

Stage II → facial palsy: oral antibiotics

Stage II → neurologic or cardiac involvement: intravenous

Stage III → lyme arthritis: initial episode → 4 wk course of oral antibiotics → joint swelling and pain can happen after 2 courses of antibiotics due to immunologic factors

what is the infectious form of the tick

larval and nymph stages

nymph causes >90% of human cases, harder to detect

both larval and nymph infect mice

• larvae becomes infected by feeding on mice and molt to nymph stage, transmitting to humans

• adult tick feeds on deers but can bite humans

how should tick be removed?

must remove within 24 hours of attachment to reduce risk of tick-borne illness

1. grasp tick with fine tweezers

2. pull straight and smoothly away from skin

3. do NOT jerk or twist

4. do NOT coat tick with anything or use heat to coax tick out

in which parts of US are people most commonly diagnosed with lyme disease?

Northeast, Mid-Atlantic, North-Central US, Midwest