Tick-borne disease

Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa.
The economic impact of tick-borne diseases is considered to be substantial in humans, and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. Most of these pathogens require passage through vertebrate hosts as part of their life cycle. Tick-borne infections in humans, farm animals, and companion animals are primarily associated with wildlife animal reservoirs. many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. The survival and transmission of these tick-borne viruses are closely linked to their interactions with tick vectors and host cells. These viruses are classified into different families, including Asfarviridae, Reoviridae, Rhabdoviridae, Orthomyxoviridae, Bunyaviridae, and Flaviviridae.
The occurrence of ticks and tick-borne illnesses in humans is increasing. Tick populations are spreading into new areas, in part due to climate change. Tick populations are also affected by changes in the populations of their hosts (e.g. deer, cattle, mice, lizards) and those hosts' predators (e.g. foxes). Diversity and availability of hosts and predators can be affected by deforestation and habitat fragmentation.
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. As the incidence of tick-borne illnesses increases and the geographic areas in which they are found expand, health workers increasingly must be able to distinguish the diverse, and often overlapping, clinical presentations of these diseases.
18 tick-borne pathogens have been identified in the United States according to the Centers for Disease Control and at least 27 are known globally. New tick-borne diseases have been discovered in the 21st century, due in part to the use of molecular assays and next-generation sequencing.
Prevention
Exposure
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% N,N-Diethyl-3-methylbenzamide (DEET), tucking their pants legs into their socks, checking for ticks frequently, and washing and drying their clothing in a hot dryer.
According to the World Health Organization, tick-to-animal transmission is difficult to prevent because animals do not show visible symptoms; the only effective prevention relies on killing ticks on the livestock production facility.
Symptoms
Ticks also have the potential to induce a motor illness characterized by acute, ascending flaccid paralysis. This condition can be fatal if not treated promptly, affecting both humans and animals. It is mainly associated with certain species of ticks. Symptoms typically ranges from fatigue, numbness in the legs, muscle aches, and, to in some cases, paralysis and other severe neurological manifestations
Tick removal
Ticks should be removed as soon as safely possible once discovered. They can be removed either by grasping tweezers as close to the mouth as possible and pulling without rotation; some companies market grooved tools that rotate the hypostome to facilitate removal. Chemical methods to make the tick self-detach, or trying to pull the tick out with one’s fingers, are not efficient methods. In Australia and New Zealand, where tick-borne infections are less common than tick reactions, the Australasian Society of Clinical Immunology and Allergy recommends seeking medical assistance or killing ticks in-situ by freezing and then leaving them to fall out to prevent allergic/anaphylactic reactions.
Diagnosis
Diagnosing tick-borne diseases involves a dual approach. Some diagnoses rely on clinical observations and symptom analysis, while others are confirmed through laboratory tests. ticks can transmit a wide range of viruses, many of which are arboviruses. In general, specific laboratory tests are not available for rapid diagnosis of tick-borne diseases. Due to their seriousness, antibiotic treatment is often justified based on clinical presentation alone.
Tick-borne encephalitis (TBE) presents non-specific clinical features, making laboratory diagnosis crucial. The diagnostic process typically involves identifying specific IgM- and IgG-serum antibodies through enzyme-linked immunosorbent assay (ELISA) since these antibodies are detectable in most cases upon hospitalization.
Assessing risk
For a person or pet to acquire a tick-borne disease requires that the individual gets bitten by a tick and that the 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 bacterium that causes Lyme disease is well understood to require a substantial feeding period. In general, soft ticks (Argasidae) transmit pathogens within minutes of attachment because they feed more frequently, whereas hard ticks (Ixodidae) take hours or days, but the latter are more common and harder to remove.
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), a nonprofit lab at the University of Massachusetts, 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 diseases in their town or state can search the LMZ surveillance database.
Examples
Major tick-borne diseases include:
Bacterial
Lyme disease or borreliosis
Organism: Borrelia burgdorferi sensu lato (bacterium)
Vector: at least 15 species of ticks in the genus Ixodes, including deer tick (Ixodes scapularis (=I. dammini), I. pacificus, I. ricinus (Europe), I. persulcatus (Asia))
Endemic to: The Americas and Eurasia
Symptoms: Fever, arthritis, neuroborreliosis, erythema migrans, cranial nerve palsy, carditis, fatigue, and influenza-like illness
Treatment: Antibiotics – amoxicillin in pregnant adults and children, doxycycline in other adults
Relapsing fever (tick-borne relapsing fever, different from Lyme disease due to different Borrelia species and ticks)
Organisms: Borrelia species such as B. hermsii, B. parkeri, B. duttoni, B. 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, Southwest
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 Laos
Vector/region(s)#1: Ixodes ricinus is the main European vector.
Symptoms: Most often small red spots, other symptoms are fever, muscle pain, headache and respiratory problems
Treatment: Broad-spectrum antibiotic therapy is needed, phenoxymethylpenicillin likely is sufficient.
Human granulocytic anaplasmosis (formerly human granulocytic ehrlichiosis or HGE)
Organism: Anaplasma phagocytophilum (formerly Ehrlichia phagocytophilum or Ehrlichia equi)
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. variabilis, D. andersoni
Region (US): Southeast, South-central, West, widespread
Viral
Tick-borne meningoencephalitis
Organism: TBEV (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
Powassan virus/deer tick virus
Organism: Powassan virus (POWV), a flavivirus from family Flaviviridae. Lineage 2 POWV is also known as deer tick virus (DTV)
Vector: Ixodes cookei, Ix. scapularis, Ix. marxi, Ix. spinipalpusm, Dermacentor andersoni, and D. variabilis
Endemic to: North America and eastern Russia
Colorado tick fever
Organism: Colorado tick fever virus (CTF), a coltivirus from the Reoviridae
Vector: Dermacentor andersoni
Region: US (West)
Crimean-Congo hemorrhagic fever
Organism: CCHF virus, a nairovirus, from the Bunyaviridae
Vector: Hyalomma marginatum, Rhipicephalus bursa
Region: Southern part of Asia, Northern Africa, Southern Europe
Severe febrile illness
Organism: Heartland virus, a phlebovirus, from the Bunyaviridae
Vector: Lone star tick (Amblyomma americanum)
Region: Missouri and Tennessee, United States
Severe febrile illness, headaches, coma in 1/3 patients
Organism: tentatively Alongshan virus, jingmenvirus group in the flavivirus family
Vector: tick (likely Ixodes persulcatus, Ixodes ricinus), mosquitoes
Region: Inner Mongolia but potentially more widespread
Protozoan
Babesiosis
Organism: Babesia microti, Theileria equi
Vector: Ixodes scapularis (deer tick), I. pacificus (western black-legged tick)
Region (US): Northeast, West Coast
Cytauxzoonosis
Organism: Cytauxzoon felis
Vector: Amblyomma americanum (Lone star tick)
Region (US): South, Southeast
Toxin
Tick paralysis
Cause: Toxin
Vector (US): Dermacentor andersoni (Rocky Mountain wood tick), D. variabilis (American dog tick or wood tick)
Region (US): D. andersoni: East, D. variabilis: East, West coast
Vector (Australia): Ixodes holocyclus (Australian paralysis tick)
Region (Australia): East
Allergies
Alpha-gal allergy - Alpha-gal syndrome is likely caused by a hypersensitivity reaction to the Alpha-gal (Galactose-alpha-1,3-galactose) sugar molecule introduced by ticks while feeding on a human host. The immune reaction can leave people with an allergy to red meat and other mammalian derived products.
See also
Arbovirus
Climate change and infectious diseases
List of diseases spread by invertebrates
List of insect-borne diseases
Mosquito-borne disease
Robovirus
Tibovirus
Ticks of domestic animals
References
External links
Tick-Borne Diseases: Recommendations for Workers and Employers—National Institute for Occupational Safety and Health
Tickborne Diseases—National Center for Infectious Diseases (CDC)
Tickborne Disease Website—Massachusetts Department of Public Health
Ixodes Scapularis—3D animation of Deer or Blacklegged Tick from US Army site
Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance Wikibooks