A REVIEW ON TICKS (ACARI: IXODOIDEA: IXODIDAE, ARGASIDAE), ASSOCIATED PATHOGENS AND DISEASES OF TRINIDAD AND TOBAGO

In this review article, the authors present an overview on ticks which are found on humans and animals in Trinidad and Tobago. Hitherto, 896 valid species of ticks are reported from throughout the world, but so far only 23 tick species belonging to seven genera have been recorded in Trinidad and Tobago. The growing significance of ticks in medical and veterinary fields emphasizes the need for further studies on the ecology of ticks and the epidemiology of tick-borne diseases.


INTRODUCTION
Ticks are interesting largely because of their considerable medical and veterinary importance (Jongejan and Uilenberg 2004) and have attracted a great deal of scientific attention due to their role as vectors of numerous pathogens (Kaufman 2010). They belong to the phylum Arthropoda, class Arachnida, order Acari. A total of 896 valid tick species (702 Ixodid,193 Argasid and 1 Nuttalliella tick (sub-) species) have been recorded from all climatic zones throughout the world (Guglielmone et al. 2010).
Ticks are blood-sucking obligatory ectoparasites of mammals, birds, reptiles and amphibians. They cause anaemia, restlessness, loss of condition, decrease in milk production and tick paralysis in animals, along with irritation by injury due to bites (Jonsson 2006). Gross lesions consist of focal erosions, erythema, crusted ulcers with alopecia and nodules in some individuals.
In addition, ticks are currently considered to be second only to mosquitoes as vectors of human infectious diseases in the world (Parola and Raoult 2001) and are known to transmit numerous arboviruses (e.g., tick-borne encephalitis virus and other Flaviviridae, several Reoviridae, Bunyaviridae, and Iridoviridae), bacteria (Rickettsia, Ehrlichia, Borrelia), and protists (Babesia and Theileria) (Sonenshine 1993). Nijhof et al. (2005) recorded the vector competence of ticks, including 808 tick-pathogen relationships: 322 relationships with 84 bacteria, 302 with 124 viruses, 143 with 59 apicomplexan parasites, 4 with 3 nematodes and 3 with Trypanosoma theileri and a further 34 species of ticks are found associated with toxicosis. These authors also recorded 233 reported cases of acaricide resistance for 20 tick species of veterinary and medical importance. The annual global cost associated with ticks and tickborne diseases in cattle alone is considered to be in the billions of US dollars (De Castro 1997).
To date, there has been no assembled list of tick species present in Trinidad and Tobago and their role in the transmission of tick-borne diseases in the country, despite evidence of their local importance to veterinary and human health. In this review, we compile such a list, evaluate the reliability of the recorded observations, and suggest focal areas for future research. REGION Cruz (2001) recorded 45 tick species from 11 genera and two families from the West Indies (the Caribbean countries). This comprised 14 species of Ornithodoros, 10 species of Antricola, nine species of Amblyomma, three species of Argas, two species each of Boophilus and Ixodes, and one species each of Parantricola, Dermacentor (Anocentor), Haemaphysalis, Aponomma, and Rhipicephalus. On the basis of a study on the vector situation of tick-borne diseases, Camus and Barré (1995) mentioned that the most important ticks transmitting diseases to ruminants in the Caribbean islands are: Amblyomma variegatum, vector of cowdriosis and associated with acute dermatophilosis; A. cajennense, potential vector of cowdriosis; Boophilus microplus, vector of babesiosis and anaplasmosis. The annual financial loss from livestock industry due to tick infestation has been estimated to be in the millions of dollars per year in Commonwealth Caribbean only (Rawlins and Mansingh 1987). It is believed that the most important tick in the Caribbean in terms of disease transmission, the tropical bont tick A. variegatum, was first imported into the area by livestock coming from West Africa to the island of Guadeloupe around the 19 th century (Uilenberg et al. 1984). It was speculated that the tick later spread to other Caribbean islands (Barré et al. 1995). A programme with the primary objective to eradicate A. variegatum from nine islands (Anguilla, Antigua and Barbuda, Barbados, Dominica, Montserrat, Nevis, St. Kitts, St. Lucia and St. Maarteen) was launched in 1994 (Pegram et al. 1998) and ended in 2008(Ahoussou et al. 2010).

TICKS IN TRINIDAD AND TOBAGO
An attempt has been made to list all tick species recorded from Trinidad and Tobago, including information on their hosts and the references (Table 1). A review of the literature revealed 23 tick species, belonging to seven genera, recorded from Trinidad and Tobago. These include nine species of the genus Amblyomma, six of Ornithodoros, two of each of the genera, Rhipicephalus, Ixodes and Argas, and one from each of the genera Dermacentor (Anocentor) and Haemaphysalis. The life cycle and control of most of these tick species, with the exception of A. cajennense and Rhipicephalus (Boophilus) microplus (Aitken et al. 1958;Thomas 1963;Smith 1973;Dindial 1977;Polar 2007), are not considered in this review. However, other available information such as the distribution, associated pathogens and effects on hosts of the 23 species are stated below, with an emphasis on the particularly problematic species.

Argas miniatus
Argas (Persicargas) miniatus was detected from chickens in Gasparee Island, Trinidad (Kohls et al. 1970). This is a common parasite of chickens in Neotropical countries which might have sometimes been misidentified as A. persicus. Many reports of A. persicus, a Palearctic species found on poultry in the Neotropics, may actually represent misidentifications of A. miniatus or another related species (Kohls et al. 1970).

Argas persicus
As mentioned above, Argas persicus, a Palearctic species, can be easily confounded with other Argas species during identification, and many reports of A. persicus on poultry in the Neotropics may actually represent misidentifications of A. miniatus or another related species (Kohls et al. 1970).

Ornithodoros (Alectorobius) denmarki
The larvae, nymphs and adults of O. (A.) denmarki, a new species , which was provisionally identified as O. (A.) capensis from Trinidad by Denmark and Clifford (1962), were found in nesting sites of sooty and noddy terns on Soldado Rock, Trinidad. Aitken et al. (1969)

Ornithodoros (Subparmatus) viguerasi
Distribution: ranges from Mexico to Argentina (Jones et al. 1972;Voltzit 2007) Amblyomma cajennense Neumann (1899) is credited for the identification of A. cajennense from Trinidad. Nuttall et al. (1926) mentioned that A. cajennense, a common tick species in the West Indies and Central and South America, was often a troublesome pest at certain seasons of the year, when the larvae swarm in thousands in the grass and herbage and attack both man and domestic animals with avidity. Aitken et al. (1958) recorded 'The 1958 Cayenne tick outbreak' at the Lagoon Doux Estate, south of Mayaro, where only the labourers showed serious effects of tick exposure, such as bout and skin irritations. These authors found A. cajennense on a variety of animals including man. Spraying dichlorodiphenyltrichloroethane (DDT), Gamma Benzene Hexachloride (GBH), chlordane and dieldrin helped to control the tick population. Smith (1973) found very large populations of A. cajennense ticks in infested areas with uncontrolled grass growth and suggested that a reduction in grass length and the removal of tree shade could help reduce the tick populations. He also studied the distribution of A. cajennense in Trinidad and Tobago; this tick was found only in Trinidad on the Cedros peninsula and on east coast at Mayaro. Smith (1974) recorded A. cajennense in ruminants, equines, dogs and man. The ecology and life cycle of this tick was also investigated by Dindial (1977) and Smith (1975), respectively. Dindial (1977) found that A. cajennense was present in the coastal regions of Manzanilla, Mayaro, Guayaguauare and the Cedros Peninsula area of Trinidad and was absent in Tobago. The presence of A. cajennense on cattle was also established by Clarkson (1969) and Rawlins (1977) in Trinidad. Lans (2002) reported a second outbreak of this tick from 1994 to 1996 in Cedros and Mayaro linked to the presence of free-ranging cattle on the coconut estates.
Distribution: ranges from southern USA to northern Argentina and Caribbean Islands (Cruz 2001;Voltzit 2007).

Amblyomma dissimile
Neumann (1899) is credited for the identification of A. dissimile in Trinidad. Nuttall et al. (1926) recorded this tick in Trinidad from snakes (Lachesis mutans) and iguanas. Turk (1948) found Amblyomma trinitatis, a synonym of A. dissimile, on a ground lizard at St. Augustine. Aitken et al. (1968a and1969) recorded A. dissimile, during their survey of arthropods for natural virus infection and found it on various species of snake, large lizards, caimans, large toads and tortoises. Dindial (1977) reported the presence of A. dissimile from iguanas, frogs and snakes both in Trinidad and Tobago. Voltzit (2007) also mentioned the presence of A. dissimile which feeds on reptiles and toads.

Amblyomma nodosum
The presence of A. nodosum, a tick that feeds on birds and anteaters, was recorded in Trinidad by several authors (Jones et al. 1972;Nava et al. 2007b;Voltzit 2007).
This tick is known to transmit rickettsial infections (Ogrzewalska et al. 2009).
Dermacentor nitens is known to transmit Babesia caballi (Equine babesiosis) (Jongejan and Uilenberg 2004). Asgarali et al. (2007) investigated 93 horses in Trinidad for serum antibodies to Theileria equi and Babesia caballi using an immunofluorescent antibody test and found 77 to be seropositive. However, the authors did not study the transmitted agents. Earlier, Floch and Fauman (1958) confirmed the presence of the tick, D. nitens, in Trinidad. Very recently, Georges (2010) diagnosed some tick-transmitted haemopathogens (Anaplasma platys, Babesia canis vogeli, B. caballi, Theileria equi) in companion animals using molecular tools.

Haemaphysalis juxtakochi
Distribution: ranges from USA to northern Argentina (Guglielmone et al. 2003) Ixodes downsi Kohls (1957) Aitken et al. (1969) recorded I. luciae during their survey of arthropods for natural viral infections. Everard and Tikasingh (1973) found I. luciae on rodents (Oryzomys capito and Proechimys guyannensis) from Turure Forest. In 1974, Smith recorded I. luciae from small wild animals from Trinidad. Distribution: Argentina, Brazil, Bolivia, Colombia, Guyana, Guatemala, Peru, Mexico, Nicaragua, Surinam, Venezuela. Belize, Costa Rica, Ecuador, French Guiana and Panama (Guglielmone et al. 2011) Rhipicephalus (Boophilus) microplus Aitken et al. (1958) recorded a few specimens of the southern cattle tick R. (B.) microplus from cattle and sheep in Trinidad. Williams and Gonzalez (1968) observed that Holstein heifers imported into Trinidad from Canada with the intent to develop a dairy industry were exposed to tick-infested pastures and that these exotic cattle suffered from a febrile disease associated with marked anaemia, occasional haemoglobinuria and sometimes death within two to six weeks after importation and introduction to tick-infested pastures. They also confirmed the detection of Babesia spp. and Anaplasma marginale from the blood of the infected cattle. This established the presence of R. (B.) microplus ticks in Trinidad, as these ticks are vectors of both the pathogens. The presence of R. (B.) microplus on cattle in Trinidad was confirmed by Aitken et al. (1969), Clarkson (1969) and Rawlins (1977). Smith (1973) studied the distribution of R. (B.) microplus in Trinidad and Tobago. Rhipicephalus (B.) microplus was found throughout both islands, except on land newly cleared from forest. Furthermore, Smith (1974) recorded this tick exploiting ruminants and equines. The prevalence and biology of R. (B.) microplus was investigated by Dindial (1977) and he also found the presence of R. (B.) microplus ticks all over the country. Spraying dichlorodiphenyltrichloroethane (DDT), Gamma Benzene Hexachloride (GBH), chlordane and dieldrin was reported to have helped to control this tick population in Trinidad. Polar and co-investigators (2005) reported the use of entomopathogenic fungi Metarhizium anisopliae to control R. (B.) microplus at Aripo livestock station in Trinidad. Polar (2007) found that Metarhizium anisopliae was effective against all development stages of R. (B.) microplus and Rhipicephalus sanguineus, except larvae of the latter.
Distribution: Cosmopolitan CONCLUSION Trinidad and Tobago harbour a high diversity of tick species, some of which are known to play a significant role in animal and human health. The reported detection of a total of 23 different tick species may be considered to be very high considering the relatively small size of the twin Island country (Trinidad -4828 km 2 ; Tobago -300 km 2 ). Tobago, being the smaller of the two islands, has fewer animal populations and recorded lower tick species richness. Amblyomma cajennense, the main species of concern to humans and animals, is found only in some pockets of Trinidad and has not been reported from Tobago. The main factor limiting the distribution of this tick appears to be its intolerance of wet soil and high rainfall. The relatively small areas infested with this species have common features such deep sandy well-drained soil with a well-marked dry season and low rainfall (Smith 1973).
All reported surveys of ticks in the Caribbean suggest the absence of Antricola mexicanus and Amblyomma variegatum in Trinidad and Tobago, except an unpublished report (Rawlins et al. 1992) and an unconfirmed record by Rawlins et al. (1993) which was published in a newsletter. Alderink and McCauley (1988) mentioned Trinidad and Tobago as one of the 12 non-infested A. variegatum island groups in the Lesser Antilles. The absence of A. variegatum in Trinidad and Tobago may be due to strict vigilance during animal importation. In addition, according to the annual report on Animal Health 2009, cowdriosis, a ricksettial pathogen transmitted by Ambylomma spp, is considered absent in Trinidad and Tobago (Anon. 2010). Though A. cajennense is an experimental and potential vector of cowdriosis, it is thought to be a poor vector as successful transmission by this tick species seems to be low (Uilenberg 1983;Jongejan 1992). Moreover, A. cajennense has not been incriminated so far in the natural transmission of this disease (http://www.oie.int). All the facts lead us to conclude that A. variegatum may be absent in this country. Hunter (1945) reported the presence of R. (B.) annulatus in Trinidad. However, Smith (1974) concluded that the presence of this species was probably an incorrect identification of R. (B.) microplus, a species found in abundance throughout Trinidad and Tobago. Subsequently, there has been no record of the presence of R. (B.) annulatus from Trinidad.
Since 1977, there has been no comprehensive study on ticks in Trinidad and Tobago and only sporadic information is available on disease transmission. Future studies on the ecology of ticks and epidemiology of tick-borne diseases in Trinidad and Tobago will therefore be rewarding, and veterinarians and researchers should be encouraged to update the list of prevalent ticks as this will lead to a better understanding of the epidemiology of tickborne human and animal diseases in the country.