Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. Tick-borne illnesses are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. Because individual ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. Currently (2016), there are 16 known tick-borne diseases of humans (four discovered since 2013).
As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, it becomes increasingly important that health workers be able to distinguish the diverse, and often overlapping, clinical presentations of these diseases.
Diagnosis and treatment
In general, specific laboratory tests are not available to rapidly diagnose tick-borne diseases. Due to their seriousness, antibiotic treatment is often justified based on clinical presentation alone.
Ticks tend to be more active during warmer months, though this varies by geographic region and climate. Areas with woods, bushes, high grass, or leaf litter are likely to have more ticks. Those bitten commonly experience symptoms such as body aches, fever, fatigue, joint pain, or rashes. People can limit their exposure to tick bites by wearing light-colored clothing (including pants and long sleeves), using insect repellent with 20%–30% DEET, tucking their pant legs into their socks, checking for ticks frequently, and washing and drying their clothing (in a hot dryer).
For a person or companion animal to acquire a tick-borne disease requires that that individual gets bitten by a tick and that that tick feeds for a sufficient period of time. The feeding time required to transmit pathogens differs for different ticks and different pathogens. Transmission of the bacteria that causes Lyme disease is well understood to require a substantial feeding period.
For an individual to acquire infection, the feeding tick must also be infected. Not all ticks are infected. In most places in the US, 30-50% of deer ticks will be infected with Borrelia burgdorferi (the agent of Lyme disease). Other pathogens are much more rare. Ticks can be tested for infection using a highly specific and sensitive qPCR procedure. Several commercial labs provide this service to individuals for a fee. The Laboratory of Medical Zoology (LMZ) is a non-profit lab at the University of Massachusetts that provides a comprehensive TickReport for a variety of human pathogens and makes the data available to the public. Those wishing to know the incidence of tick-borne disease in their town or state can search the LMZ surveillance database.
Major tick-borne diseases include:
Lyme disease or Borreliosis
Organism: Borrelia burgdorferi sensu lato (bacterium)
Vector: deer tick (Ixodes scapularis (=I. dammini), I. pacificus, I. ricinus (Europe), I. persulcatus (Asia))
Endemic to: North America and Eurasia
Symptoms: Fever, arthritis, neuroborreliosis, erythema migrans, cranial nerve palsy, carditis, fatigue, and influenza-like illness.
Treatment: Antibiotics (Doxycycline in non pregnant adults, Amoxicillin in pregnant adults and children)
Relapsing fever (Tick-borne relapsing fever, different from Lyme disease due to different Borrelia species and ticks)
Organisms: Borrelia species Such as Borrelia hermsii, Borrelia parkeri, Borrelia duttoni, Borrelia miyamotoi
Vector: Ornithodoros species
Regions : Primarily in Africa, Spain, Saudi Arabia, Asia in and certain areas of Canada and the western United States
Symptoms: Relapsing fever typically presents as recurring high fevers, flu like symptoms, headaches, and muscular pain, with less common symptoms including rigors, joint pain, altered mentation, cough, sore throat, painful urination, and rash.
Treatment: antibiotics are the treatment for relapsing fever, with doxycycline, tetracycline, or erythromycin being the treatment of choice.
Typhus Several diseases caused by Rickettsia bacteria (below).
Rocky Mountain Spotted Fever
Organism: Rickettsia rickettsii
Vector: wood tick (Dermacentor variabilis), D. andersoni
Region (US): East, South West
Vector: Amblyomma cajennense
Region (Brazil): São Paulo, Rio de Janeiro, Minas Gerais.
Symptoms:Fever, headache, altered mental status, myalgia, and rash.
Treatment: Antibiotic therapy, typically consisting of doxycycline or tetracycline.
Helvetica Spotted fever
Organism: Rickettsia helvetica
Region(R Helvetica): Confirmed common in ticks in Sweden, Switzerland, France and in Laos
Vector/Region(s)#1 : Ixodes ricinus is the main European vector
Vector/Region(s)#2: Please add if more vectors are found.
Symptoms:Most often small red spots, other symptoms are fever, muscle pain, headache and respiratory problems
Treatment: Broad band Antibiotic therapy are needed, it is likely that phenoxymethylpenicillin is sufficient.
Ehrlichiosis anaplasmosis (formerly human granulocytic ehrlichiosis or HGE)
Organism: Ehrlichia chaffeensis, E. equi (renamed to Anaplasma phagocytophilum, see Human granulocytic anaplasmosis for another example)
Vector: lone star tick (Amblyomma americanum), I. scapularis
Region (US): South-Atlantic South-Central
Bartonella: Bartonella transmission rates to humans via tick bite are not well established but Bartonella is common in ticks. For example: 4.76% of 2100 ticks tested in a study in Germany
Tularemia
Organism: Francisella tularensis, A. americanum
Vector: D. andersoni, D. variabilis
Region (US): Southeast, South-Central, West, Widespread
Tick-borne meningoencephalitis
Organism: TBEV aka FSME virus, a flavivirus from family Flaviviridae
Vector: deer tick (Ixodes scapularis), Ixodes ricinus (Europe), Ixodes persulcatus (Russia + Asia))
Endemic to: Europe and Northern Asia
Colorado tick fever
Organism: Colorado Tick Fever virus (CTF), a coltivirus from Reoviridae
Vector: Dermacentor andersoni
Region: US (West)
Crimean-Congo hemorrhagic fever
Organism: CCHF virus, a nairovirus, from Bunyaviridae
Vector: Hyalomma marginatum, Rhipicephalus bursa
Region: Southern part of Asia, Northern Africa, Southern Europe
Severe Febrile IllnessOrganism: Heartland virus, a phlebovirus, from Bunyaviridae
Vector: Lone Star Tick (Amblyomma americanum)
Region: Missouri and Tennessee, United States
Babesiosis
Organism: Babesia microti, B. equi
Vector: I. scapularis, I. pacificus
Region (US): Northeast West Coast
Cytauxzoonosis
Organism: C. felis
Vector: D. variabilis (American Dog Tick)
Region (US): South, Southeast
Tick paralysis
Cause: Toxin
Vector (US): D. andersoni, D. variabilis West
Region (US): East
Vector (Australia): Ixodes holocyclus
Region (Australia): East
