Central America contains an approximate area of 522,000 km
2 integrating a wide biological diversity, which includes a rich fauna of ticks, with about 80 species reported to date (
Supplementary Dataset S3). Of this diversity of ticks,
Amblyomma mixtum,
Amblyomma ovale,
Dermacentor nitens,
R. microplus,
Rhipicephalus sanguineus s.l.,
Alectorobius puertoricensis, and
Alectorobius talaje have been reported as relevant to human and animal health due to their role as vectors of pathogens causing rickettsiosis, ehrlichiosis, anaplasmosis, relapsing fever, and babesiosis, as well as causing paralysis and severe allergies.
Central America has a long-standing history in relation to cases of human and animal parasitism, with the first records of effects on humans being recorded in the 19th century in Guatemala (Ornithodoros talaje and Amblyomma sabanerae). At the beginning of the 20th century, the first reports of clinical cases of tick-borne pathogens in humans were reported in Panama (Rickettsia rickettsii relapsing fever and spotted fever) and Costa Rica (R. rickettsii spotted fever). In fact, rickettsiosis is the most important group of diseases reported in Central America, since there are confirmed fatal cases in these two countries, in addition to reports of severe rickettsiosis in acute patients from Guatemala, Honduras, and Nicaragua.
Other microorganisms detected in ticks from Central America include the genera Ehrlichia (E. canis, E. cf. chaffeensis), Anaplasma (A. marginale, A. phagocitophylum, A. platys), Borrelia (B. puertoricensis, Borrelia burgdorferi group), and hemoparasites like Babesia (B. odocoilei, B. vogeli) and Hepatozoon (H. canis, Hepatozoon spp). There is also serologic evidence of ehrlichiosis, anaplasmosis, and babesiosis in domestic animals; a probable case of canine ehrlichiosis in a boy from Panama and serology compatible with ehrlichiosis in human blood from Costa Rica.
2.4. Brazil
Brazil is a vast and ecologically diverse country with several distinct biomes that include tropical forests (Amazon and Atlantic rainforest), savannah (Cerrado), grasslands (Pampa), semi-arid (Caatinga), and the world’s largest tropical wetland (Pantanal). These biomes are characterized by their unique climate, vegetation, and wildlife. However, huge areas within each biome were transformed into anthropogenic landscapes to become part of the Global Human Ecosystem. This ecological mosaic has shaped the current Brazilian tick fauna and associated microbiota, but general knowledge about most tick species is lacking, and epidemiological data about transmitted pathogens are also scarce. Indeed, knowledge of tick-borne diseases is primarily related to those agents with a major impact on human welfare.
The tick fauna of the country is by now composed of 78 species, 53 Ixodidae and 25 Argasidae.
Amblyomma remains as the richest, with 34 valid species
[51]. The original tick fauna was modified by the introduction of exotic species, outstandingly
R. microplus and two species of the
Rhipicephalus sanguineus complex
[52][53][54].
Undoubtedly, the cattle tick
R. microplus is a species that raises an important level of apprehension. It is the species most associated with economic losses throughout a country that had a commercial herd estimated at 224.6 million heads in 2022
[55]. In the last broad assessment of the negative impact of the cattle tick, an annual loss of USD 3.24 billion was estimated
[56]. This loss includes the negative impact of infections caused by the major cattle tick-borne pathogens
Babesia spp. and
Anaplasma marginale and the disease commonly known as “Bovine parasitic sadness”
[57].
The main horse ticks in the country are
Amblyomma sculptum and
Dermacentor nitens (named previously
Amblyomma cajennense and
Anocentor nitens)
[58]. Among tick-borne diseases, equine piroplasmosis caused by
Babesia caballi and
Theileria equi infection is enzootic in Brazil
[59][60]. Several tick species are supposed to transmit these pathogens but
D. nitens is considered the sole vector of
B. caballi, while
T. equi is transmitted by
R. microplus and possibly by
A. sculptum [60][61].
In relation to dogs, the anthropogenic landscapes throughout Brazil are widely colonized by ticks of the
R. sanguineus complex with a wide distribution in anthropized areas of the country
[53]. These species, particularly the tropical lineage (recently considered
Rhipicephalus linnaei [62]), are vectors of
Ehrliquia canis and
Babesia vogeli, the agents, respectively, of canine monocytic ehrlichiosis and canine piroplasmosis, collectively known by pet owners as the “tick disease” (in Brazilian Portuguese, “doença do carrapato”). Both
E. canis and
B. vogeli have been widely reported in dogs from Brazil
[63][64]. These tick species have been found infected with
R. rickettsii [65], nonetheless human rickettsiosis caused by infected tick bite remains elusive. On the other hand,
Amblyomma aureolatum, a species restricted to the Atlantic rainforest and the Pampa biome in the south of the country
[66][67], is the natural vector of
Rangelia vitalii, the etiologic agent of canine rangeliosis, the most severe canine piroplasmosis of the western hemisphere
[68].
Dogs are also involved in the epidemiology of human tick-borne rickettsiosis and should be considered a target species for tick control. Only two tick-borne
Rickettsia species have been proven to cause human disease in Brazil,
R. rickettsii, causing a frequently lethal disease, and
Rickettsia parkeri strain Atlantic rainforest, responsible for milder non-lethal rickettsiosis
[69]. Circumstantial evidence indicates that there is in the country a third and mild rickettsiosis caused by
Rickettsia parkeri stricto sensu
[70]. Wild carnivores are hosts for the adult ticks of
Amblyomma aureolatum,
Amblyomma ovale, and
Amblyomma tigrinum and domestic dogs are common alternative hosts
[71]. These tick species have been shown to be infected with, respectively,
R. rickettsii,
Rickettsia parkeri Atlantic rainforest strain, and
Rickettsia parkeri sensu stricto and emerging knowledge indicates that dogs may bridge the infected ticks to human households
[70][72][73]. Whereas
Rickettsia-infected
A. ovale ticks have a wide distribution within the country, infected
A. tigrinum were detected only in the southern region
[70].
Rickettsia rickettsii infection is the major human tick-borne disease in Brazil, the “febre maculosa Brasileira” (Brazilian spotted fever). Although the disease has a low prevalence and is overwhelmingly restricted to specific areas, it has gained significant attention and apprehension in society due to its high lethality. In fact, timely and correct antibiotic treatment is curative. Unfortunately, early diagnosis is not easy and relies on epidemiological data (febrile individuals bitten by ticks in endemic areas) since laboratory diagnosis is typically confirmatory after the recovery or death of those who are ill
[74].
A controversial tick-borne disease in Brazil is Lyme borreliosis. Lyme-like disease has been diagnosed since 1992
[75][76]. The disease is routinely diagnosed based on clinical and serological data and records of suspected cases included in the Brazilian Ministry of Health database
[76]. There are also occasional molecular identification reports of bacteria from the
Borrelia burgdorferi sensu lato complex
[77]. However,
Borrelia burgdorferi has not yet been isolated either from humans or ticks
[78][79] and the ecological background to sustain its epidemiology within the country is weak.
Viruses are also significant tick-borne agents, and tick-associated viruses have already been documented in Brazil
[80][81]. However, their role as pathogens remains uncertain. Indeed, there are numerous molecular studies reporting other potential tick-borne pathogens in ticks collected from domestic animals, wild animals, and the environment in Brazil.
2.5. Europe
Ticks are an important part of the parasitic burden affecting livestock in Europe, as well as a growing issue regarding human health because of the transmission of pathogens. In Europe, prominent species of ticks affecting domestic animals (with even 6–7 generations per year, like
R. microplus in many parts of the world) are absent, but reported species also represent an important burden in animal husbandry. The panorama is a wide repertoire of species, most of them affecting livestock, that colonize areas with very different environmental conditions therefore resulting in a “mosaic” of distribution
[82][83][84][85][86], with different seasonal activity periods, ability to transmit different types of pathogens, and capacity to spread throughout the wild fauna of a region.
Most of these ticks have generalist feeding habits, affecting notably domestic ruminants and horses under extensive management. They constitute a large burden affecting the production of meat or milk, debilitating the animals and/or increasing abortions, favoring poor health conditions, and promoting the development of secondary diseases caused by opportunistic bacteria
[85]. An additional issue is the use of acaricides against ticks, which contribute to contamination by these toxic products and the increase in the costs of management of the animals. It is important to note that most (if not all) species of ticks affecting livestock are shared with wild ungulates. Therefore, due to the co-existence of wildlife and livestock in large European regions, efforts to control or eradicate ticks are challenging. As in other regions, ticks prevail in nature through cycles of infestation affecting either domestic or wild ungulates as adults, with the immatures feeding commonly on many species of birds and rodents
[86].
Europe can be roughly divided, according to latitude, into three regions, Mediterranean, Central, and Northern regions. The Mediterranean region is populated by species of ticks with an obvious seasonality because of the seasonal nature of the weather in the region. The most important species belong to the genera Rhipicephalus and Hyalomma. Due to the vegetal characteristics of the region, sheep and goats are the main livestock present in the area (high humidity deficit, high temperature), making these species the main vectors for several species of protozoans, like Babesia spp. and Theileria spp., or bacteria like Anaplasma ovis or Rickettsia spp.
Central Europe, including the British Isles and southern parts of Scandinavia and Finland, is the major area of distribution of the prominent species I. ricinus and H. punctata. These two species tend to concentrate on ruminants and are the main vectors of several species of protozoans of the genus Babesia and the bacterium Anaplasma phagocytophilum. Both pathogens are responsible for a wide array of clinical presentations, from the chronic one, with a course of abortions and serious weight loss, to the acute cases, in which death may be fast, even in 72 h. No efforts to determine the economic losses produced by these protozoans or bacteria have been addressed.
Most, if not all, species affecting livestock and pets in Europe may bite humans with a different pressure according to the climate gradient associated with the territory and with pathogen transmission. The pathogens carried by ticks are supported by populations of wild vertebrates, that have a different prominence according to the composition of the community of vertebrates
[87].
Other than pets, for which harmonized guidelines about tick control exist and owners commonly follow recommendations by veterinarians, there are no agreed protocols for tick control in Europe. Control (or attempt at eradication) of ticks depends on the perception of the owners, the recommendation of field veterinarians, and the availability of adequate acaricides, which may have different regulations depending on the country. The lack of harmonized protocols prevents the necessary joint effort to eradicate ticks.
2.6. Egypt
In Egypt, animal trade, climate, and anthropogenic factors contribute to the spread of tick species and TBD. The spillover of various tick-borne pathogens is likely to occur from sub-Saharan Africa and other Mediterranean basin countries. The development of acaricide resistance further exacerbates the widespread presence of ticks and TBD, posing a significant economic challenge in Egypt
[88][89]. To date, eight tick species from the family Argasidae and forty-four species from the family Ixodidae have been reported, with
Hyalomma sp. and
Rhipicephalus sp. being the most common.
Enhancing the understanding of ticks and their associated diseases among various societal sectors, as well as the general population, is crucial for implementing effective control measures. In Egypt, ticks and TBD have predominantly been viewed through the lens of agricultural production rather than human health. Farmers’ perception is limited due to the widespread use of acaricides to eradicate ticks infesting animals, leading to the development of acaricide resistance
[90][91].
Considering the close interaction between humans, animals, and tick vectors, a multidisciplinary approach linking human, animal, and environmental health within a “One Health” framework is essential. Systematic and comprehensive surveillance studies investigating ticks and TBD in defined areas are needed. Collaborative efforts between Egypt and Europe, combining fieldwork, research capacity, and funding, could lead to a better understanding of the epidemiological landscape of ticks and TBD.
2.7. Uganda
In Uganda, ticks including Rhipicephalus appendiculatus, Rhipicephalus decoloratus, Amblyomma variegatum, and Rhipicephalus evertsi evertsi are the most economically important ticks that parasitize cattle and transmit deadly disease pathogens. The key tick-borne disease pathogens are Theileria parva, Babesia bovis, B. bigemina, A. marginale, and Ehrlichia ruminantium whose infections result in high morbidity and mortality if naïve cattle become infected. These diseases and the tick vectors cause annual losses of USD 1.1 billion, thus affecting cattle-keeping communities in poverty.
However, the current tick control approaches mainly depend on the use of acaricides applied at a frequency of one to three times a week depending on the extent of the tick burden. The increasing frequency of application is critically indicative of acaricide-resistant tick genotypes
[92].
The specific deleterious effects of tick infestations are bites which damage the hides in animals with high tick loads, blood loss and thus anemia, allergy due to toxins in tick saliva, chronic stress, and continuous irritation affecting animal welfare, leading to immuno-depression and loss of energy
[93].
Generally, more than 70% of Uganda’s population depends on agriculture for their livelihood, and the animal industry accounts for 17% of the national gross domestic product. Cattle farmers perceive ticks and tick-borne diseases as a big limitation to commercial livestock farming given the fact that transmitted pathogens limit the breeding of high-yielding cattle. The overdependence on acaricide for tick control is no longer viable, thus demanding the development of novel control strategies.
2.8. Nigeria
The study of ticks and tick-borne diseases in Nigeria has a long history
[94][95][96][97], with a recent resurgence of interest in investigating these pathogens
[98][99][100][101][102][103][104]. Ticks are widely distributed across the country, affecting various animal hosts, including wild game and trans-border cattle. Various studies have reported on the distribution of ticks on different animal hosts across the country, including wild game animals and cattle that enter through trans-border routes
[99][100][101][107][108][109][110][111][112][113]. Southern and Northern Nigeria both report the presence of tick genera. However, factors like unrestricted animal movement, lack of robust quarantine regulations, and favourable climate contribute to tick distribution.
Notable tick-borne diseases in Nigeria include Babesiosis, Anaplasmosis, Theileriosis, and Ehrlichiosis
[105][106], while diseases like Crimean-Congo hemorrhagic fever and African tick-bite fever are underreported. Human impact and prevalence of tick-borne diseases are poorly understood, and tick bites are often inadequately addressed.
Future efforts should encompass a nationwide survey of ticks and tick-borne pathogens in both animal and human populations. Raising awareness, particularly among at-risk groups like farmers, hunters, foresters, and veterinarians, is crucial. Additionally, addressing acaricide resistance is essential, as some pastoralists unknowingly use harmful chemicals on animals, posing risks to public health and the environment.
2.9. India
In India, 109 tick species are reported to infest animals
[116]. The tick index or tick burden in cattle was reported to be 0.922 to 1.0
[117][118] and the species diversity was high in rural parts in comparison to urban areas. As per a recent estimate, the TBD in animals is causing an economic loss of USD 787.63 million/year. Besides animals, several tick species such as
Amblyomma integrum,
Haemaphysalis spinigera,
Dermacentor auratus,
Hyalomma isaaci,
Rhipicephalus haemaphysaloides,
R. sanguineus s.l., and
Otobius megnini are reportedly infesting human beings
[119][120]. The use of acaricides by swabbing, dipping, spraying, pour-on, spot-on, and injection is the sole approach adopted for tick control. Awareness on environmental tick control or off-the-host tick control is lacking. No commercial anti-tick vaccines against the major cattle tick
R. microplus/
H. anatolicum are available which could be attributed to the diversity of targeted antigen sequences across the tick isolates in India
[121].
The TBDs affecting humans are Kyasanur forest disease (KFD), CCHF, Ganjam virus (GANV), Bhanja virus (BHAV), Lyme disease, Q fever, rickettsial infections (
Rickettsia conorii and
R. rickettsii), and babesiosis (
Babesia microti)
[122]. Meanwhile, animals suffer from theileriosis, babesiosis, anaplasmosis, ehrlichiosis, hepatozoonosis, and lumpy skin disease virus. There are only two licensed vaccines available against TBD in India, viz., tropical bovine theileriosis (Rakhsavac-T) and KFD for humans. Chemotherapy is the only option being practiced, controlling major TBD infections.
In rural communities, tick infestation is considered as one of the many problems animals have to suffer perennially and that is managed by washing animals, by rubbing them with dry fodder, or by the application of available acaricides at the local market when infestation is visible. In the organized sector, highly tick-susceptible cross-bred animals are maintained for higher production. The problem of ticks is regularly treated by the use of acaricides but without a strict adherence to the recommendation of the manufacturers. Although farmers are well aware of the high cost involved in the treatment of TBD, due to limited knowledge of the methods for tick control, resource-poor farmers face severe economic distress.
2.10. Nepal
In the Nepalese context, there are inadequate studies on hard ticks and hard tick-borne diseases (HTBDs). In the hills and plains of western and central Nepal, the abundant cattle ticks are
Rhipicephalus (Boophilus) microplus, Haemophysalis spp.,
Ixodes spp., and
Amblyomma spp.
[123][124]. Six species of
Haemophysalis, five species of
Rhipicephalus, and one species each of
Amblyomma and
Ixodes were reported from goats of Chitwan District
[125]. Interestingly, two species of hard ticks (
Amblyomma grevaisi and
Amblyomma varanense) were identified in snakes of Nepal, and
Amblyomma grevaisi was detected almost 100 years ago
[126].
Similar to hard tick studies, scanty research has been carried out in Nepal on characterizing the HTBDs. In a serological study in Banke and Surkhet Districts
[123], a 6.4% infection rate of TBDs was reported in cattle with
Anaplasma marginale (5.8%) followed by
Babesia bovis (0.6%).
Rickettsia honei was reported in one human patient infested with ticks
[127]. Lyme disease (caused by the tick-transmitted spirochaete
Borrelia burgdorferi) was reported for the first time in 2018 in Kaski District
[128] and a subsequent case was reported in a patient from Gulmi District
[129]. Canines transmit vector-borne diseases at the wild–domestic interface. Particularly, infections in stray dogs are alarming in Kathmandu Valley, where 81.43% of the stray dogs are infected by at least one vector-borne pathogen (
Anaplasma platys (31%),
Babeisa vogeli (13%),
Babesia gibsoni (23%)) and 41.43% are co-infected with more than one vector-borne disease
[130].
2.11. Indonesia
Geographically, Indonesia is an archipelagic country on the equator, known as having almost the most biodiversity in the world, second only to the Brazilian Amazon. The islands in eastern Indonesia are part of the Australasian continent and have different germplasm biodiversity than the western islands. The area inside of the Wallacea Webber lines holds various endemic species. In the past, research by Hoogstral, Anastos, and their colleagues contributed significantly to our understanding of tick biodiversity in Indonesia, with more than 55 tick species reported to infest different animals in the region. Some of them have particular endemic hosts, such as
Amblyomma robinsoni of
Varanus komodoensis,
Amblyomma babirussae of
Babirussa babyrussa,
Aponomma komodoense of
Varanus komodoensis, and
Amblyomma soembawensi of
Varanus salvator [131]. The most frequently reported ticks affecting livestock and companion animals include
R. sanguineus s.l., several clades of
R. microplus (that may result in several species after adequate studies),
Rhipicephalus pilans, and
Haemaphysalis bispinosa [132][133][134]. Tick-borne diseases are reported mainly from highly populated areas like Java and Bali. Tick-borne pathogens in companion animals are
Ehrlichia sp.,
Babesia sp., and
Anaplasma sp. whereas livestock are infected by
Babesia bigemina,
B. bovis,
Babesia naoakii,
Theileria orientalis,
Theileria sp.,
A. marginale, and
Coxiella burnetti [134][135][136][137][138][139].
Tick-borne diseases pose a significant growing threat, mainly due to human activity and current climate trends. Recently, there has also been an upsurge in the number of tourists visiting remote islands in the region, leading to increased interest in these areas beyond Bali and Lombok. While the recent development progress in these regions benefits the nation’s growth, it poses a significant risk of exposure to ticks and tick-borne diseases from unknown areas that can be transmitted to new hosts. Although cases of ticks and tick-borne diseases are persistently reported, rural and urban societies pay less attention to them than mosquito-borne illnesses.
2.12. Turkey
Turkey is situated at the intersection of Asia, Europe, and Africa. This unique position allows the inclusion of different climatic regions, habitat types, and animal diversity, all of which provide suitable conditions to harbor different tick species. Moreover, Turkey contains migration routes and breeding and wintering areas of many migratory birds which bring together the risk of introduction and establishment of different tick populations and associated pathogens
[140][141]. More than 40 tick species have been reported in the country to date
[142]. The most-recorded species were
H. marginatum, Hyalomma excavatum, Hyalomma anatolicum, Hyalomma asiaticum, Hyalomma aegyptium, R. sanguineus s.l.,
Rhipicephalus turanicus, Rhipicephalus bursa,
Haemaphysalis parva, and
Dermacentor marginatus [143][144][145][146][147][148][149]. As a result of this tick species richness, a number of pathogens have been detected, including
Ehrlichia canis,
Theileria spp. (
Theileria ovis, T. annulata),
Anaplasma spp. (
A. marginale, A. phagocitophylum, A. platys, A. ovis, A. centrale, A. bovis),
Borrelia spp. (
B. burgdorferi s.l.,
B. turcica),
Babesia spp. (
Babesia ovis,
B. bovis,
B. bigemina,
Babebsia major,
Babebsia crassa, Babebsia canis, and
B. divergens),
Rickettsia spp. (
Rickettsia aeschlimannii, Rickettsia hoogstraali, Rickettsia barbariae), and
Hepatozoon canis [150][151][152][153][154][155][156]. Furthermore, a considerable number of tick-borne viruses have been reported
[157][158][159][160]. Lyme borreliosis and tick-borne encephalitis (TBE) are not prevalent in Turkey, although
I. ricinus, the vector of these diseases, is widely distributed in the northern parts of the country
[161][162][163][164].
CCHF constitutes a significant public health threat in Turkey since the first case was reported in 2002. Based on official records, 10,562 cases have been recorded from 2002–2017 and 501 of them resulted in death (
https://hsgm.saglik.gov.tr/tr/zoonotikvektorel-kkka, accessed on 6 October 2023). Crimean-Congo hemorrhagic fever cases were mostly documented in rural areas in the central and northern regions of the country where agricultural and animal husbandry activities are common. Following the diagnosis of CCHF in Turkey, studies predominantly concentrated on the detection of CCHFV in ticks collected from these endemic regions
[142][165][166][167][168][169].
2.13. Australia
Girt by sea, Australia has been in complete isolation for 40 million years. This separation has led to the evolution of 70 characterized species of argasid and ixodid ticks that have co-evolved with Australia’s unique mammalian (e.g.,
Ixodes ornithorynchi, platypus tick, and
Amblyomma triguttatum, the ornate kangaroo tick), avian (e.g.,
Argas robertsi, Roberts’ bird tick), and reptilian (e.g.,
Amblyomma albolimbatum, stumpy-tailed lizard tick) fauna
[170]. The most common biting ticks in Australia include
I. holocyclus and
A. triguttatum on the east and west coasts that parasitize people, respectively;
Haemaphysalis longicornis and Rhipicephalus australis for cattle; and
R. linnaei for dogs. It has been hypothesized that hard ticks evolved in the part of Gondwana that later became Australasia (~120 million years ago), evidenced by the basal lineage of Metastriata, Bothriocrotoninae, and Australian lineages of
Ixodes, unique to Australia
[171]. Despite Australia’s isolation, five tick species have been introduced into the Australian continent due to the movement of domestic animals following the arrival of Europeans in 1788
[172]. This introduction has led to the incursion of several tick-borne pathogens that affect companion and livestock animals in Australia, including
A. platys,
B. vogeli,
Borrelia persica,
T. orientalis complex, and more recently,
H. canis and
E. canis. Regarding human TBDs, only three are formally accepted: Queensland spotted fever, Flinders Island spotted fever, and Q fever
[173].
The advancement of molecular techniques in recent years has led to the exponential discovery of several taxa of interest (TOIs; taxa closely related to known global tick-borne pathogens) identified within Australian ticks, wildlife, and domestic animals
[174]. TOIs include
Borrelia tachyglossi harbored within the echidna tick
Bothriocroton concolor and several closely related unnamed
Borrelia spp. in
Bothriocroton undatum and within introduced and native rodents; a whole suite of
Anaplasmatacae,
Francisellaceae,
Midichloriaceae,
Coxiellaeceae,
Bartonellaceae,
Mycoplasmatcceae, and
Rickettsiaceae species, including
Neoehrlichia australis and
Neoehrlichia arcana,
Midichloria mitochondrii, Coxiella massiliensis, hemotropic mycoplasmas and novel species of
Anaplasma,
Ehrlichia,
Rickettsia,
Francisella; rhabdoviruses, chuviruses, coltivurses, flavivurses, and jingmenviruses; lastly, hemoprotozoa have also been recently discovered, including
Thelieria spp.,
Babesia spp.,
Trypanosoma spp., and
Hepatozoon spp.
[174][175][176][177][178][179][180][181][182][183][184][185]. The genetic diversity of these TOIs mirrors the co-evolution of ticks and native wildlife. Furthermore, the uniqueness of these microbes answers why standard genus-specific and even species-specific assays from the northern hemisphere have failed in previous years to characterize tick-borne microbes in Australian ticks.