Transmission of Lyme Disease
Ticks become infected with the bacterium while feeding on an infected reservoir host. The most common hosts for larvae and nymphs are the white-footed mouse and birds. White tailed deer are the principal host for the adult ticks, but they do not become infected with Lyme disease. Rather, they are responsible for transporting ticks and maintaining tick populations in the wild. The white-footed mouse is the reservoir for the infection, and the tick is the vector.
This short video summarizes the key steps in transmission of Lyme disease.
Humans get Lyme disease after being bitten by an infected tick. Since ticks are obligate feeders, they need to attach to a host and take a blood meal in order to survive. Adult ticks climb to the tops of grasses and shrubs, where they wait for a large mammal host by "questing", i.e., perching on the ends of blades or grass or twigs, as illustrated below. When an unsuspecting human brushes against tall grass or leaves, the tick latches on and begins to bite the host. The image below shows a tick questing on the tip of a plant.
Mosquitoes land on a host and quickly bite and feed, but ticks are much slower. Ticks grasp the skin surface and cut into it over a period of 10-60 minutes. Once the skin is penetrated, the tick flues itself in place by secreting a sticky substance to hold its mouth in place. This allows the tick to feed gradually over a period of days. The smaller mouthparts on larval and nymphal ticks penetrate less deeply and evoke a smaller host reaction. Adults, however, can penetrate into the subdermal layer of skin making tick removal more difficult. The image below iis a diagram showing insertion of a tick during feeding.
It usually takes about 48 hours for the pathogen to be transmitted, so it is important to remove the tick properly as soon as it is found.
Ticks can attach themselves to any part of the body. While moist and warm areas (such as the armpits, bellybutton, back of the knees, ears, neck, groin area, etc.) tend to attract more ticks, a tick can attach itself anywhere on the skin and transmit the disease. A tick bite is not necessarily painful, which is why it is important to check for ticks everyday.
Treatment of Tick Bites
When a tick is found to be attached, it should be removed promptly with thin-tipped tweezers at a 90 degree angle, making sure to grasp the tick as close to the skin as possible and pull upward with steady pressure, as illustrated in the image below.
It is important to remove the entire tick in one piece. The area where the tick was attached should be disinfected with rubbing alcohol or other disinfectant. The individual should retain the tick in a small plastic vial and take it to a health care provider as soon as possible.
The video below shows the correct method for removing a tick.
If an individual is bitten by a tick, a physician should be consulted if the answers to the following questions are "yes."
- Can the tick be identified as a deer tick? TLink to Tick Identification Card
- Was the tick attached for at least one full day?
- Has it been less than three days since you removed the tick?
Many tick bites do not result in infection, and when infection does occur, most patients will manifest the characteristic skin rash. At present there is no evidence to support the use of prophylactic antibiotics after a tick bite in the absence of symptoms (see IDSA Guidelines). However, the treating physician may recommend a single dose of doxycycline to adults or children when all of the following conditions are met:
- The attached tick can be reliably identified as an adult or nymphal I. scapularis tick that is estimated to have been attached for less than 36 hours on the basis of the degree of engorgement of the tick with blood or of certainty about the time of exposure to the tick;
- Prophylaxis can be started within 72 hours of the time that the tick was removed;
- Ecologic information indicates that the local rate of infection of these ticks with B. burgdorferi is greater than20%; and
- Doxycycline treatment is not contraindicated.
|Proper tick removal
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Other Modes of Transmission
According to the CDC, there is no evidence that Lyme disease can be transmitted from person-to-person by touching, kissing or having sex with a person who has Lyme disease.
Transmission During Pregnancy & Breastfeeding
Lyme disease acquired during pregnancy may lead to infection of the placenta and possible stillbirth, however, no negative effects on the fetus have been found when the mother receives appropriate antibiotic treatment. There are no reports of Lyme disease transmission from breast milk.
Borrelia can live in blood stored for donation, and individuals being treated for Lyme disease with antibiotics should not donate blood. However, there are no reported cases of transmission of Lyme disease from blood donors.
Transmission from Pets
Dogs and cats can get Lyme disease, but there is no evidence that they can transmit Lyme disease to humans. Nevertheless, pets can bring infected ticks into your home or yard. Owners should discuss the use of tick control products for their pets with a veterinarian.