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Acta Tropica

Volume 223, November 2021, 106085
Acta Tropica

Soft ticks (Acari: Argasidae) in the island nations of Southeast Asia: A review on their distribution, associated hosts and potential pathogens

https://doi.org/10.1016/j.actatropica.2021.106085Get rights and content

Highlights

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    This article reviews the species of soft ticks (Acari: Argasidae) and their associated hosts and pathogens in the island nations of Southeast Asia, which consist of Malaysia (both Peninsula and Borneo), Singapore, Brunei, Indonesia, Timor-Leste, and the Philippines.

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    The most prevalent soft tick genus in the island nations of Southeast Asia is the Carios genus, and the host species most associated with findings of soft ticks in this region are bats, particularly of the genera Eonycteris, Pipistrellus, Scotophilus, and Rousettus.

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    The only known pathogens originating from soft ticks in the island nations of Southeast Asia was the Keterah virus, which was isolated from the Argas pusillus tick in Malaysia.

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    We provide a list of soft tick species and a pictorial summary of the geographical distribution of soft ticks in the island nations of Southeast Asia.

Abstract

Soft ticks (Acari: Argasidae) are the second major family of the blood feeding metastriates and vectors of a number of viral and bacterial pathogens for both humans and animals. Despite the growing effort on tick surveillance and studies worldwide, there is still limited information on the soft tick distribution in the island nations of Southeast Asia, especially species that are medically and veterinarily important. With the aim to provide an overview of the current status of knowledge on soft tick distribution in the island nations of Southeast Asia (Malaysia, Singapore, Brunei, Indonesia, the Philippines and Timor-Leste), this article reviews the species of soft ticks (Acari: Argasidae) and their associated hosts and pathogens, with the addition of a pictorial summary and list of tick species discovered in this region. The most prevalent soft tick genus is Carios, and the host species most associated with findings of soft ticks in this region are bats, particularly of the Pteropodidae and Vespertilionidae families. Furthermore, the only known pathogen originating from soft ticks in the island nations of Southeast Asia was the Keterah virus, which was isolated from Argas pusillus tick in Malaysia.

Introduction

Ticks of the Argasidae family are notably distinguished by their leathery integument, lacking a dorsal shield (scutum) in contrast to hard ticks (Ixodidae) (Service, 2012). Compared to their ixodid sister group, argasid ticks are mainly nidicolous or endophilic and preferably inhabit sheltered areas such as caves, nests and burrows of animal hosts, as well as human housings (Vial, 2009). Soft ticks usually spend 15-30 minutes of time per feeding event (Estrada-Peña, 2015) and feed multiple times between life stages. Soft ticks can transmit pathogens from their midgut into the host via saliva secretions (Chmelar et al., 2016), but in some cases pathogens are also able to be transmitted by coxal fluid into the feeding lesion (Kaufman, 2010).

The distribution of argasid ticks can be considered cosmopolitan as there are both reports on soft tick sightings and case reports of soft tick bites on humans throughout the world (Guglielmone et al., 2010; Manzano-Román et al., 2012; Fois et al., 2016; Hosseini-Chegini et al., 2019; Petney et al., 2019). However, the distribution of species in the Argasidae family can be quite scarce, especially in Southeast Asia. A recent review by Petney et al. (2019) covers argasid species found in continental Southeast Asia but information on the soft tick distribution in the island nations, which encompass Malaysian Borneo, Indonesia, the Philippines, Singapore, Brunei and Timor-Leste, is still scarce (Table 1, Fig. 1).

Since knowledge on soft tick species and their distribution across the island nations is beneficial in terms of human an animal health, this review aims to provide an overview of the current studies on soft tick distribution in the mentioned island nations of Southeast Asia.

This review is constructed using available information acquired from the Google Scholar database. The literature search was performed using the database search engine with general keywords such as ‘argasid+southeast+asia’, followed by specific ones such as ‘argasid+malaysia’

Section snippets

Argas ticks

The soft ticks of the Argas genus (Fig. 2) are identified by their flattened body margins, lateral sutural lines, and leathery, folded cuticle which result in their button-like appearance (Nicholson et al., 2019). The genus has 57 species in total and Argas ticks are known to parasitize bats and birds, with a few species infesting wild terrestrial mammals and Galapagos giant tortoises (Levin, 2020a). Argas ticks have a worldwide distribution, with most species dwelling in arid environments or

Peninsular Malaysia

The first report on soft ticks in the peninsula was presumably documented by Stanley Hirst in 1929, who discovered the bat tick Ornithodoros batuensis (later redescribed as Carios batuensis) in Batu Caves, Selangor (Hirst, 1929). In 1955, J. L. Harrison found found the cave nectar bat Eonectyris spelaea (Dumbleton, 1958) hosting C. batunensis, which was confirmed by subsequent collections and fauna surveys (McClure et al., 1967). According to the authors, all stages of both engorged and

Conclusions

Although there are quite some studies conducted on soft ticks in Southeast Asia, the information on tick distribution is still limited today and mostly outdated. Moreover, the knowledge on vector competence for various pathogens in the island nations of Southeast Asia remains scarce, and more research and surveillance are needed. Information or reports of soft tick bites on humans are likely severely underreported, even though there are species that are known to attack humans (A. boueti, A.

Declaration of Competing Interest

The authors declare that they have no competing interest.

Acknowledgements

All authors would like to thank the Faculty of Medicine of Universiti Teknologi MARA (UiTM) Sungai Buloh campus and the Institute of Medical Molecular Biotechnology (IMMB) from Malaysia and the Bernhard Nocht Institute for Tropical Medicine from Hamburg, Germany for their constant support.

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