Tick-borne disease | |
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Specialty | Infectious disease |
Tick-borne diseases, which afflict humans and other animals, are caused by infectious agents transmitted by tick bites. [1] They are caused by infection with a variety of pathogens, including rickettsia and other types of bacteria, viruses, and protozoa. [2] The economic impact of tick-borne diseases is considered to be substantial in humans, [3] and tick-borne diseases are estimated to affect ~80 % of cattle worldwide. [4] 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. [5] Many tick-borne infections in humans involve a complex cycle between wildlife animal reservoirs and tick vectors. [5] 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. [6]
The occurrence of ticks and tick-borne illnesses in humans is increasing. [7] Tick populations are spreading into new areas, in part due to climate change. [8] [9] 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. [8]
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. [2] 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. [10]
As of 2020 [update] 18 tick-borne pathogens have been identified in the United States according to the Centers for Disease Control [10] and at least 27 are known globally. [8] [11] [12] New tick-borne diseases have been discovered in the 21st century, due in part to the use of molecular assays and next-generation sequencing. [13]
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. [14] [15]
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. [16]
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. [17]
Tick-borne diseases (TBD) are a major health threat in the US. The number of pathogens and the burden of disease have been increasing over the last couple decades. With improved diagnostics and surveillance, new pathogens are regularly identified, bettering our understanding of TBDs. Unfortunately, diagnosis of these illnesses remains a challenge, with many TBDs presenting with similar nonspecific symptoms and diagnosis requiring a battery of assays to assess patients adequately. New advanced molecular diagnostic methods, including next-generation sequencing and metagenomics analysis, promise improved detection of novel and emerging pathogens with the ability to detect a litany of potential pathogens with a single assay. [18]
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. [19] 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. [20] [21]
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.
Diagnosing Lyme borreliosis relies on clinical criteria, with a history of a tick bite and associated symptoms being crucial. Laboratory diagnosis follows a 'two-tiered diagnostic protocol,' involving detecting specific antibodies using methods such as immunoenzymatic assays and Western blot tests, preferably with recombinant antigens. While ELISA and Western blot have similar sensitivity, Western blot is more specific due to the identification of specific immunoreactive bands. Seroconversion typically occurs around two weeks after symptom onset, but false positive ELISA results can be linked to poorly reactive antibodies against specific antigens, especially in patients with other infectious and non-infectious diseases. [22]
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. [23]
Patients with Lyme disease who are treated with appropriate antibiotics usually recover rapidly and completely. Antibiotics commonly used include doxycycline, amoxicillin, or cefuroxime axetil. For Anaplasmosis, ehrlichiosis and Rocky Mountain spotted fever, Doxycycline is the first line treatment for adults and children of all ages. For babesiosis, a combination therapy with atovaquone and azithromycin is most commonly recommended for treatment of mild to moderate babesiosis. Treatment is usually continued for 7 to 10 days. A combination regimen of oral clindamycin and quinine has also been proven effective, but the rate of adverse reactions is significantly higher with this combination. For Powassan virus, there are no medications for treating Powassan virus infections. Medications, however, can help to relieve symptoms and prevent complications. People with severe disease are typically treated in a hospital where they may be given intravenous fluids, fever-reducing medications, breathing support, and other therapies as needed. [24]
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. [25] 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. [19]
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 [26] for a variety of human pathogens and makes the data available to the public. [27] Those wishing to know the incidence of tick-borne diseases in their town or state can search the LMZ surveillance database. [27]
Major tick-borne diseases include:
Ticks are parasitic arachnids of the order Ixodida. They are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. The timing of the origin of ticks is uncertain, though the oldest known tick fossils are from the Cretaceous period, around 100 million years old. Ticks are widely distributed around the world, especially in warm, humid climates.
Lyme disease, also known as Lyme borreliosis, is a tick-borne disease caused by species of Borrelia bacteria, transmitted by blood-feeding ticks in the genus Ixodes. The most common sign of infection is an expanding red rash, known as erythema migrans (EM), which appears at the site of the tick bite about a week afterwards. The rash is typically neither itchy nor painful. Approximately 70–80% of infected people develop a rash. Early diagnosis can be difficult. Other early symptoms may include fever, headaches and tiredness. If untreated, symptoms may include loss of the ability to move one or both sides of the face, joint pains, severe headaches with neck stiffness or heart palpitations. Months to years later, repeated episodes of joint pain and swelling may occur. Occasionally, shooting pains or tingling in the arms and legs may develop.
Tick-borne encephalitis (TBE) is a viral infectious disease involving the central nervous system. The disease most often manifests as meningitis, encephalitis or meningoencephalitis. Myelitis and spinal paralysis also occurs. In about one third of cases sequelae, predominantly cognitive dysfunction, persist for a year or more.
Borrelia burgdorferi is a gram-negative bacterial species of the spirochete class in the genus Borrelia, and is one of the causative agents of Lyme disease in humans. Along with a few similar genospecies, some of which also cause Lyme disease, it makes up the species complex of Borrelia burgdorferi sensu lato. The complex currently comprises 20 accepted and 3 proposed genospecies. B. burgdorferi sensu stricto exists in North America and Eurasia and until 2016 was the only known cause of Lyme disease in North America.
Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia. It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.
Relapsing fever is a vector-borne disease caused by infection with certain bacteria in the genus Borrelia, which is transmitted through the bites of lice, soft-bodied ticks, or hard-bodied ticks.
Babesia, also called Nuttallia, is an apicomplexan parasite that infects red blood cells and is transmitted by ticks. Originally discovered by the Romanian bacteriologist Victor Babeș in 1888, over 100 species of Babesia have since been identified.
Powassan virus (POWV) is a Flavivirus transmitted by ticks, found in North America and in the Russian Far East. It is named after the town of Powassan, Ontario, where it was identified in a young boy who eventually died from it. It can cause encephalitis, inflammation of the brain. No approved vaccine or antiviral drug exists. Prevention of tick bites is the best precaution.
Anaplasmosis is a tick-borne disease affecting ruminants, dogs, and horses, and is caused by Anaplasma bacteria. Anaplasmosis is an infectious but not contagious disease. Anaplasmosis can be transmitted through mechanical and biological vector processes. Anaplasmosis can also be referred to as "yellow bag" or "yellow fever" because the infected animal can develop a jaundiced look. Other signs of infection include weight loss, diarrhea, paleness of the skin, aggressive behavior, and high fever.
Lyme disease, or borreliosis, is caused by spirochetal bacteria from the genus Borrelia, which has 52 known species. Three species are the main causative agents of the disease in humans, while a number of others have been implicated as possibly pathogenic. Borrelia species in the species complex known to cause Lyme disease are collectively called Borrelia burgdorferisensu lato (s.l.), not to be confused with the single species Borrelia burgdorferi sensu stricto, a member of the complex, which is responsible for nearly all cases of Lyme disease in North America.
Ixodes scapularis is commonly known as the deer tick or black-legged tick, and in some parts of the US as the bear tick. It was also named Ixodes dammini until it was shown to be the same species in 1993. It is a hard-bodied tick found in the eastern and northern Midwest of the United States as well as in southeastern Canada. It is a vector for several diseases of animals, including humans and is known as the deer tick owing to its habit of parasitizing the white-tailed deer. It is also known to parasitize mice, lizards, migratory birds, etc. especially while the tick is in the larval or nymphal stage.
Powassan encephalitis, caused by the Powassan virus (POWV), a flavivirus also known as the deer tick virus, is a form of arbovirus infection that results from tick bites. It can occur as a co-infection with Lyme disease, as both are transmitted to humans by the same species of tick. Over the last decade, there has been a surge in the number of cases and an expansion of its geographic range. In the United States, cases have been documented primarily in the northeast. The disease was first isolated from the brain of a boy who died of encephalitis in Powassan, Ontario, in 1958. This disease is classified as a zoonosis, originating in animals, often found in rodents and ticks, with subsequent transmission to humans. The virus shares antigenic similarities with the Far Eastern tick-borne encephalitis viruses.
Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by ticks of the Ixodes ricinus species complex, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.
Ticks are insects known for attaching to and sucking blood from land-dwelling animals. Ticks fall under the category of 'arthropod', and while they are often thought of in the context of disease transmission, they are also known to cause direct harm to hosts through bites, toxin release, and infestation. Infestation can cause symptoms ranging from mild to severe and may even cause death. Hosts can include any number of vertebrates, though humans and livestock are more likely to be the interest of researchers.
Deer tick virus (DTV) is a virus in the genus Flavivirus spread via ticks that causes encephalitis.
Rickettsia australis is a bacterium that causes a medical condition called Queensland tick typhus. The probable vectors are the tick species, Ixodes holocyclus and Ixodes tasmani. Small marsupials are suspected reservoirs of this bacterium.
Borrelia miyamotoi is a bacterium of the spirochete phylum in the genus Borrelia. A zoonotic organism, B. miyamotoi can infect humans through the bite of several species of hard-shell Ixodes ticks, the same kind of ticks that spread B. burgdorferi, the causative bacterium of Lyme disease. Ixodes ticks are also the primary vector in the spread of babesiosis and anaplasmosis.
Tibovirus is a term often used to describe viruses that are transmitted by tick vectors. The word tibovirus is an acronym. This falls within the superorder arthropod thus tibovirus is classified under Arthropod Borne virus (Arborvirus). For a person to acquire infection the tick must bite and feed for a sufficient period of time. The tiboviruses that affect humans are limited to within 3 families: Flaviviridae, Reoviridae, and Bunyaviridae.
Borrelia mayonii is a Gram-negative, host-associated spirochete that is capable of causing Lyme disease. This organism can infect various vertebrate hosts such as humans via the bite of a black legged tick.
Global climate change has increased the occurrence of some infectious diseases. Infectious diseases whose transmission is impacted by climate change include, for example, vector-borne diseases like dengue fever, malaria, tick-borne diseases, leishmaniasis, zika fever, chikungunya and Ebola. One mechanism contributing to increased disease transmission is that climate change is altering the geographic range and seasonality of the insects that can carry the diseases. Scientists stated a clear observation in 2022: "The occurrence of climate-related food-borne and waterborne diseases has increased ."