Lyme disease is most commonly transmitted by the bite of a tick. A tick study conducted by the Texas Department of State Health Services from 1990 to 1992 found ticks infected with Borrelia burgdorferi the causative agent of Lyme disease, in every public health region of Texas with an infection rate of 1 to 4% in each region. No follow-up to this study has ever been made.
Vector Transmission At the time of the study, the Borrelia found in Texas ticks was characterized as a Lyme-like disease. Lyme disease was believed to be transmitted only by deer ticks found in the northeastern United States (Ixodes scapularis). Texans, however, were being infected by bites from other species of ticks that prey on dogs, cattle, horses, birds and rodents, as well as deer ticks. Since that time, a number of different Borrelia strains have been discovered, all of which produce symptoms consistent with Lyme disease. Research published by the Entomological Society of America, based on the Texas Department of Health study, found the etiologic agent of Lyme borreliosis in several species of ticks, including Amblyomma americanum, Amblyomma maculatum, and Ixodes scapularis Say, and one flea species, Ctenocephalides felis. Ticks were collected from state parks or wildlife conservation areas.
Although a variety of ticks were included in the study, the conclusion reached was that in Texas, the most common vector of Lyme borreliosis was the A. Americanum tick, the lone star tick (so-called because of the white, star-like shape on its back), an aggressive species that will feed on a variety of hosts, including dogs, other domestic animals, and humans. This finding was consistent with the experience Texas patients have reported.
Just as the CDC has strict reporting requirement for Lyme cases, it also maintains a strict definition of Lyme. Its website still reports that Lyme is transmitted by two species of Ixodes ticks, black-legged ticks, one on the East Coast and one on the West. It has labeled the borreliosis transmitted by A. americanum, the lone star tick, as STARI, Southern Tick-Associated Rash Illness, which it says is not as severe as Lyme disease. The CDCs website says that the cause of STARI is still unknown. CDC studies have only involved cases in which a rash was present.
Most patient advocate groups contend that various strains of borrelia can produce similar symptoms and that the distinction the CDC makes in its strict definition of Lyme disease does not serve patients with Lyme-like symptoms. It is so difficult to test for Borrelia burgdorferi or to cultivate it in the laboratory that, coupled with a lack of funds for adequate research, it may be decades before research proves all the ways that Lyme can be transmitted. Until then, any tick bite should be treated with caution.
A misconception about Lyme disease is that a tick must be attached to a person for 48 hours before transmission of the disease can occur. Transmission has now been documented in a pediatric case with a tick attachment of only 30 minutes. Probability of transmission, however, does increase over a longer period of attachment.
Although there is no research on other insect vectors, patients have reported being bitten by black flies and mosquitoes before they got Lyme. Since these insects can transmit other dangerous diseases, it is best to play safe and avoid being bitten by them, as well, by using insect repellant containing DEET.
Blood transfusion The CDC reports that the borrelia that causes Lyme disease can live in blood that is stored for transfusion. Patients with Lyme should not donate blood.
Sexual transmission Some patients have long believed that they contracted Lyme sexually. The CDC adamantly denies that Lyme disease can be transmitted sexually. The CDC assumes that these are cases in which family members, exposed to the same environment, have each been bitten by a tick.
Many doctors who treat thousands of Lyme patients have seen evidence that Lyme can be sexually transmitted, based on the histories of their patients.
In 2011, the first documented case of an insect-borne disease being transmitted sexually was reported in the Journal of Emerging Infectious Diseases. Although this was a virus and not the bacteria that causes Lyme disease, it has raised questions in the Lyme community.
It may be many years before this debate is settled.
Congenital Lyme The CDC reports that Lyme disease can infect the placenta and cause stillbirths. Pregnant women with Lyme disease should be treated with antibiotics during their pregnancies to minimize the risk to the fetus.
The CDC denies that Lyme can be transmitted in utero to an unborn baby. As with sexual transmission, many patients who have been sick since birth believe they contracted Lyme in their mothers womb. It is important to realize how difficult it currently is to prove this scientifically. Children are not tested for Lyme unless they have developed symptoms, up until which time, they could have been exposed to a tick.
In 2001, Tessa D. Gardner, MD, of Washington University School of Medicine in St. Louis, published research in Infectious Diseases of the Fetus and Newborn Infant, based on 263 cases of neonatal Lyme gathered from medical literature before 1998. Her findings showed that 25% resulted in adverse outcomes: 8% in fetal death and 2% in neonatal death. Fifteen percent of the babies were born alive but were ill or had an abnormality.
This followed the research of Alan B. McDonald who, in 1989, documented that transplacental transmission of the spirochete from mother to fetus was possible.
In 2003, Dr William Harvey and Dr. Patricia Salvato of Houston published an article in Medical Hypotheses reporting their findings of both sexually-transmitted Lyme and congenital Lyme, backed by animal studies and a preponderance of data that contradicts the CDC model of Lyme. This model specifies the criteria of EM rash, tick attachment history, or endemic region of residence (Northeast or West Coast). It defines Lyme as a zoonotic infection (one transmitted by insects) and therefore, ignores any other possible cause.
Again, this is a subject that is hotly debated between the academic community and clinicians who treat many Lyme cases. Regardless of whether fetuses can be infected with Lyme, since there is universal agreement that the placenta can be infected, pregnant women with Lyme should be treated with antibiotics under the care of a physician expert in Lyme disease.