Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
What diseases do ticks transmit (act as vectors) to humans?
Although most tick bites do not transmit pathogens, some bites do. It is not
possible to determine if a tick is carrying pathogens visually. The following is
a list of all of the major tick-borne diseases, the usual tick vector(s), and
the pathogen(s) the tick transmits that may occur in the United States.
Tularemia -- Dermacentor variabilis (American dog tick; several species are also known as a wood tick) (hard tick) and
Amblyomma americanum or lone star tick (hard tick) -- vectors for Francisella
Anaplasmosis (human granulocytic anaplasmosis or HGA) -- Ixodes species
(hard tick) -- vectors for Anaplasma phagocytophilum bacteria
Colorado tick fever -- Dermacentor andersoni (hard tick) -- vectors for
Coltivirus, a RNA virus
Powassan encephalitis -- Ixodes species and Dermacentor andersoni (both
hard ticks) -- vectors for Powassan encephalitis virus, an RNA arbovirus
Babesiosis -- Ixodes species (hard ticks) -- vectors for Babesia, a
Ehrlichiosis -- Amblyomma americanum or lone star ticks;
see photo below with "lone star" mark on the dorsal surface (hard ticks) --
vectors for Ehrlichia chaffeensis and Ehrlichia ewingii bacterial species
Rocky Mountain spotted fever -- Dermacentor variabilis (American dog tick,
see picture below) and
Rocky Mountain wood tick (Dermacentor andersoni) (hard tick) are the primary
vectors and occasionally the brown dog tick (Rhipicephalus sanguineus);
Amblyomma cajennense (hard tick) is the vector in countries south of the U.S. -- vectors for Rickettsia bacteria.
Picture of an American dog tick; SOURCE: CDC
Lyme disease -- Ixodes species including deer ticks or also known as black-legged ticks (hard ticks,
see photo below) -- vectors
for Borrelia species of bacteria
Picture of a deer tick; SOURCE: CDC/Anna Perez
Heartland virus -- a viral disease discovered in 2012 transmitted by Amblyomma americanum or lone star tick
Picture of a lone star tick; SOURCE: CDC/Dr. Amanda Loftis, Dr. William Nicholson, Dr. Will Reeves, Dr. Chris Paddock
Tick-borne relapsing fever -- Ornithodoros moubata or African tick;
see illustration below (soft
tick) -- vectors for Borrelia species of bacteria
Picture of a soft tick; SOURCE: CDC
Q fever -- Rhipicephalus sanguineus, Dermacentor andersoni (see photo below), and
americanum (all three are hard ticks) -- vectors for Coxiella burnetii, a
Picture of a Rocky Mountain wood tick; SOURCE: CDC/Dr. Christopher Paddock
Southern tick-associated rash illness (STARI) -- Amblyomma americanum or
lone star tick (hard tick) -- infectious agent not yet identified according to
U.S. Centers for Disease Control and Prevention (CDC)
This list shows that some ticks (for example, Ixodes) can transmit more than
one type of pathogenic microbe (virus, bacteria, and protozoa). It is possible
to transmit more than one pathogen in a single tick bite, although this rarely
occurs. Outbreaks of tick-related illnesses follow seasonal patterns (about
April to September in the U.S.) as ticks evolve from larvae to adults.