Comments on distribution and ecology
The ticks Reticulinasus salahi were collected in two separate periods. In 1951–1966, the species was described and the first data on its natural history were gathered. Several species of hosts were documented at that time: Rousettus aegyptiacus, Eptesicus serotinus, Taphozous perforatus, Myotis sp. [= Otonycteris hemprichii], and Homo sapiens. The records were made mainly in Egypt and additionally also in Israel, Jordan, and Spain (Hoogstraal 1953; Theodor and Costa 1960; Estrada-Peña et al. 1989; Saliba 1990; Benda et al. 2010). In 2005–2019, the records are available only from two host species, Rousettus aegyptiacus and Otonycteris hemprichii, collected in their roosts. The latter records findings come from specialised trips organised to investigate the bat fauna of the Middle East (Benda et al. 2007, 2010, 2012).
Species of the genus Reticulinasus parasitize predominantly pteropodid bats. The majority of R. salahi records originates from Rousettus aegyptiacus or from the roosts of this bat; this clearly indicates this bat is the primary host of R. salahi. The distribution of this tick follows the distribution of the primary host, as Hoogstraal (1953) already concluded (see Fig. 4). However, R. salahi has been repeatedly collected also from Otonycteris hemprichii in Jordan, from the eastern desert region, far away from the range of Rousettus aegyptiacus (Azraq-Shishan and Shawmari; Saliba et al. 1990; Benda et al. 2010). The combination of the genera Rousettus and Otonycteris as the main (known) hosts is rather unusual, these bats differ in their ecology and although their distribution ranges are generally similar to each other, in the Middle East they overlap only marginally. In the Palaearctic, R. aegyptiacus depends in its occurrence mostly on the human cultivation of desert oases with date palm growing, otherwise it occurs only in warm areas rich in natural fruit production and cave presence (e.g., the Nile valley, Yemeni and Omani mountains). On the other hand, O. hemprichii is a desert bat, roosting mainly in rock fissures. The use/disuse of cave roosts is the main difference in ecology between these hosts – Rousettus uses caves and cave-like spaces, while Otonycteris does not. The parasite transfer most likely took place in anthropogenous conditions, since both host species use parts of buildings as their roosts at a certain level. This suggests that the transfer of the ticks between the hosts is a matter of relatively short history, several thousand years at maximum when the fruit bat started to follow the human cultivation of oases. Moreover, the fruit bat can move effectively over large distances, as the food and roost sources are rare and dispersed unevenly. On the other hand, Otonycteris is known as a rather sedentary species and thus, it can be regarded it rather as a secondary host of Reticulinasus salahi. Thus, the transfer of this parasite between host species seems to have been driven by the human presence in the arid environment.
The records of R. salahi from other bat species and humans can be explained similarly as already Hoogstraal (1953: 261) did in the case of the record from Taphozous perforatus, see as follows: “The single exception was found on a tomb bat, Taphozous perforatus perforatus E. Geoffroy, from Sultan Hassan Mosque. This host was in a group resting near fruit bats. Because other bats very seldom rest near fruit bats in this area, and we have found larvae on none other than fruit bats and the single neighboring tomb-bat, it seems reasonable to assume that fruit bats are the chief hosts and other kinds are attacked only under special local conditions”. We agree with such a view, it conforms with all records of R. salahi made from other host species.
On the other hand, we regard the finding of R. salahi from Eptesicus serotinus in Prat de Llobregat (Barcelona), Spain (Estrada-Peña et al. 1989), as dubious. Regarding the geographic distance to other record sites and the reported host species, we consider the species identification of the tick as erroneous, at least temporarily, until other records supporting such geographically and ecologically extraordinary findings are available. Estrada-Peña et al. (1989) considered this record unusual and accidental. In the western part of the Mediterranean, the bat species of the genus Eptesicus are primary hosts of other tick species, Secretargas transgariepinus (Beaucournu and Clerc 1968; Médard et al. 1997; own unpublished data from Morocco).
Hoogstraal and Kaiser (1958: 54) reported as follows: “People who venture into Egyptian caves and buildings infested by fruit bats are frequently bitten by this parasite [= R. salahi]”. The experience with R. salahi indicates that it is a parasite of bats and humans, while in other vertebrate species, it “fed reluctantly” and “having engorged succumbed within a few days” (Lavoipierre and Riek 1955: 101). The evolution trajectory to the use of the genus Homo as a host has an origin only in the common use of identical shelters with bats, both natural caves and man-made buildings.
The Murine gammaherpesvirus 68 (MHV-68) presence
We selected the MHV-68 virus for testing in Reticulinasus salahi because it was recently confirmed to be positively present in various European and American bat species (Briestenská et al. 2018; Janíková et al. 2020). The MHV-68 virus was isolated for the first time in the 1980s from small ground rodents in Slovakia (Blaškovič et al. 1980; Mistríková and Blaskovic 1985). The rodents are considered one of the main reservoirs from which the MHV-68 virus can spread through direct contact (via urine, saliva) or airway to other animal species inhabiting the same habitat (Hricová and Mistríková 2008). The presence of antibodies to this virus was described also in several large wild and domestic species of mammals, including humans (Wágnerová et al. 2015). These findings suggest that the MHV-68 virus is widespread in nature, most probably without geographical boundaries; besides Slovakia, it was found in Ukraine, Slovenia, and Mexico. It could be distributed among various hosts using vectors that are likely various ticks species (Kúdelová et al. 2015, 2017, 2018; Hájnická et al. 2017). This tick-borne pathogen circulates among small rodents and larger mammals through horizontal transmission from an infected tick to an uninfected mammal host and vice versa (Hájnická et al. 2017).
The habitats occupied by bats (e.g. cave systems) are physically rather isolated from those inhabited by other mammalian groups and horizontal and vertical transmission of a virus may seem to be more complicated. However, it may follow a completely different scenario.
The tick species that commonly parasitize rodents and other mammals, like Ixodes ricinus, are rarely found in bats. However, the transmission of these ticks to the bat hosts is possible when the bats forage in low vegetation (Siuda et al. 2009). Many bat species are foliage-gleaners foraging in shrublands and meadows (see e.g., Goiti et al. 2008), where such parasite transfer seems to be well possible. The tick Ixodes ricinus has been also found inside caves in the proximity of bats, having been transported there by bats as described above or having moved from a different mammalian species (a record under a colony of Rhinolophus euryale Blasius, 1853, in the Jasovská jaskyňa Cave, Slovakia; own unpubl. data). The presence of the tick Ixodes ricinus in the Palaearctic was confirmed in both rhinolophid and vespertilionid bats in different areas from western Europe to Transcaucasia (Italy, Canestrini 1890; Greece, Arthur 1963; Austria, Sixl et al. 1972; Spain, Sanchez-Acedo et al. 1975; Azerbaijan, Gadžiev and Dubovčenko 1975; Gadžiev et al. 1990; Germany, Walter 1985; Ukraine, Nikitičenko 1990; Slovakia, Poland, Siuda et al. 2009; Ševčík et al. 2010). These countries delineate the entire extent of the distribution range of the tick.
The design of vertical transmission of the MHV-68 virus isuncertain. On one hand, Hricová and Mistríková (2008) suggested that the virus can spread through direct contact (urine, saliva) or airway to other animal species inhabiting the same habitat and in such a case, it can be completed via bat urine that is excreted to either cave floor or directly onto animals that occur on the cave floor. On the other hand, Aligo et al. (2015: 330) concluded that the MHV-68 virus is not horizontally transmitted among laboratory mice by cage contact. In natural conditions, Francois et al. (2013) expected the transmission between mouse individuals to happen only by sexual contact.
Ixodes ricinus occurs in the arid parts of the Middle East only in a smaller extent and very locally (Mazyad et al. 2010; Alkishe et al. 2017). The more widely distributed Reticulinasus salahi apparently takes over the role of the vector of the MHV-68 virus in these subtropical parts of the Palaearctic, at least to a small extent.
Our results conform with the hypothesis that the MHV-68 virus is a globally widespread herpesvirus capable of frequent inter-species transmission, thanks to suitable vectors. Reticulinasus salahi is another species of ticks which can serve as a reservoir of the virus and can play an important role in its ecology and epidemiology.
Bacteria and piroplasms
The reason for our search of bacteria and piroplasmid pathogens in Reticulinasus salahi is clear; there is no information on its vectorial capacity, although several cases of human infestation by this tick species are known. More than twenty species of bacteria and piroplasmida were reported to be present in two argasid tick species parasitizing bats, Secretargas transgariepinus and Carios vespertilionis, namely of the genera Rickettsia Da Rocha-Lima, 1916, Coxiella Philip, 1948, Ehrlichia Moshkovski, 1945 /Anaplasma Theiler, 1910, Bartonella Strong, Tyzzer, Brues et Sellards, 1915, Borrelia Swellengrebel, 1907, and Babesia Starcovici, 1893 (see Colas-Belcour 1933; Sándor et al. 2021).
However, the genera Bartonella and Babesia were not found in our examined samples of Reticulinasus salahi. On the other hand, a positivity for Borrelia burgdorferii s.l. was confirmed in the larvae samples of R. salahi collected from Otonycteris hemprichii in Jordan and Rousettus aegyptiacus in Oman. This pathogen has been also found as other argasid ticks and in many other arthropod parasites of bats in the western Palaearctic, see Hubbard et al. (1998).
Positivity for bacteriae of the genus Rickettsia, belonging to the Rickettsia slovaca cluster, was confirmed in the samples of R. salahi from Otonycteris hemprichii originating in Jordan. Rickettsia slovaca Řeháček, 1984 is a human pathogen (Cazorla et al. 2003), it was isolated for the first time from the tick Dermacentor marginatus (Sulzer, 1776) from Slovakia in 1968 (Řeháček 1984). Its occurrence was then documented in several species of ticks of the genus Dermacentor Koch, 1844 in western Europe, and central and eastern Asia, viz. D. marginatus, D. reticulates Fabricius, 1794, and D. silvarum Olenev 1931 (Eremeeva et al. 1993; Beati et al. 1993, 1994; Balayeva et al. 1994; Raoult et al. 2002; Tian et al. 2012). This tick genus was found accidentally also in bats; Neumann (1911) and Senevet (1937) reported records of D. reticulatus from two bat host species, Rhinolophus clivosus Cretzschmar, 1828 and Miniopterus schreibersii (Kuhl, 1817), in the western Palaearctic (without site specification). The tick D. marginatus was found to parasitize Pipistrellus pipistrellus (Schreber, 1774) in Iran (Fillipova et al. 1976), Myotis blythii (Tomes, 1857) and Rhinolophus euryale Blasius, 1853 in Azerbaijan (Gadžiev and Dubovčenko 1975; Gadžiev et al. 1990). These tick species thus could be a source of pathogen presence also in R. salahi and in its hosts.
Positivity for Candidatus Ehrlichia shimanensis was confirmed in one larva of R. salahi collected from Rousettus aegyptiacus in Oman. Up to the present, the Candidatus Ehrlichia shimanensis was known from the temperate zone of eastern and central Asia, it was found in wild populations of wild deer and small rodents, but also in the tick Haemaphysalis longicornis Neumann, 1901 (Kawahara et al. 2006; Rar et al. 2008). However, the transmission ways of this pathogen also remain unknown.
Rousettus aegyptiacus, the primary host of R. salahi, has a strategy of roost switching and simultaneously, it shares its roosts with other bat species. This indicates more possible directions of the bacteria and piroplasmid transfers. Within its distribution range, R. aegyptiacus represents an exclusive host of certain arthropod parasites which could participate in the pathogen transfers (e.g., Diptera: Eucampsipoda aegyptia Macquart, 1851; Acarina: Ancystropus zeleborii Kolenati, 1857, Meristaspis lateralis Kolenati, 1857). However, an interaction with other host bat species cannot be excluded in these parasites (see e.g., Theodor 1955,1967, Rudnick 1960). On the other hand, the pathogen transmission could be realised by a polyvalent parasite, accidentally parasitizing R. aegyptiacus. The argasid ticks of the Carios vespertilionis group could be such a parasite type, they were reported to be frequent hosts of the mentioned pathogen genera. Up to now, in R. aegyptiacus two other ticks were found, viz. Carios vespertilionis in Sudan (Hoogstraal 1956) and Jordan (Benda et al. 2010), and Chiropterargas boueti in Egypt and Sudan (Hoogstraal 1952, 1955, 1956). However, also other bat parasite groups occurring within the distribution range of R. aegyptiacus can be included in the group of potential vectors of these pathogens, such as Polyctenidae, Streblidae and/or Macronyssidae in Egypt (Frauenfeld 1856; Kolenati 1856; Maa 1961), and/or Nycteribiidae in Israel and Lebanon (Theodor and Moscona 1954; Benda et al. 2016). On the other hand, up to now, only one pathogen has been isolated from the bat hosts of R. salahi (i.e. from R. aegyptiacus and also from T. perforatus), the bacterial genus Grahamella in Egypt (Mohammed and Saoud 1964, 1965).
In conclusion, Reticulinasus salahi clearly seems to be a potential segment in the transfer route for a variety of pathogens between various host species, at least three species of bats of three families, Rousettus aegyptiacus, Taphozous perforatus, and Otonycteris hemprichii, and the human.