Global Health: the tick that binds us all

Review of the biology and ecology of Haemaphysalis longicornis Neumann, 1901 

By Dina M. Fonseca, Andrea Egizi, James Occi, Center for Vector Biology, Rutgers, the State University of New Jersey

[Nov 20, 2017 – version updated with input from James Mertins, USDA-NIFA]

longicornis1550Rev

Figure 1 – Three life-stages of H. longicornis. Adult female (left), partially engorged nymph (center) and larvae (right). Scale is millimeters.

Haemaphysalis longicornis are three-host hard ticks (Ixodidae) originally from northeast Asia, where they survive harsh winters. They thrive in tall grasses (meadows, paddocks) in areas where average precipitation is higher than 50 mm/month (1). In the late 1800’s they expanded into Australia (possibly with cattle brought in from Japan) and later into New Zealand. Of note, most of the ecological/ behavioral literature refers to these invasive populations, although there has been a recent increase in studies from its native range, where it has been declared a vector of the bunyavirus that causes severe fever with thrombocytopenia syndrome (SFTS), a human hemorrhagic fever (2, 3).

This species is the only tick known to parasitize cattle in New Zealand, earning it the name of “NZ cattle tick”. In the US, “cattle tick” is reserved for Rhipicephalus (Boophilus) annulatus. Instead the common name “longhorned tick”, a direct translation of its scientific name has been used. Another common name that may be apt is “bush tick”, but the best common name to use if it becomes established in the US has not yet been decided. Also of note, there has been some confusion in the literature between H. longicornis and H. bispinosa primarily because early authors called the parthenogenetic forms H. bispinosa and the bisexual ones H. longicornis. This confusion has persisted in China until recently (4). See section on “H. longicornis vs. H. bispinosa” below on ways to differentiate them.

H. longicornis feeds readily on cattle, sheep, horses, domesticated deer and other livestock and can reach such large numbers they weaken the animals (especially the young) and in some cases kill them (5). They can also transmit pathogens of veterinary importance as well human pathogens (see Vector Potential section) as they often bite humans, especially those tending livestock.

Overall, the primary limiting factors to the establishment of the species seem to be temperature and humidity but there appears to be considerable difference in cold hardiness among populations. For example, in Hokkaido, the northermost Japanese island, as well as in SE Russia and in Northern China, diapausing nymphs survive harsh winters (Tmin < – 2 °C, or ~28 °F), indicating these populations are well adapted to the cold (5, 6). By contrast, invasive populations occur in areas with milder climates, and no evidence of diapause has been found in parthenogenetic New Zealand nymphs (1). In fact the low temperature extremes that eggs are capable of surviving differ markedly between Hokkaido and Australian strains (7, 8)

Life cycle and Phenology

Like all hard ticks, H. longicornis larvae emerge from eggs laid in the soil and have three active developmental stages (Figure 1, Figure 2), 6-legged larvae, 8-legged nymphs, and 8-legged adults, all feeding exclusively on vertebrate blood. H. longicornis ticks move on and off hosts three times, as the blood meal is a necessary preamble to molting to the next stage and eventually for egg development. The invasive form of H. longicornis is parthenogenic (females lay viable eggs without mating), and so males are extremely rare (see section on Genetics).

Slide1

Figure 2 – Schematic diagram of annual temporal patterns of occurrence of the different developmental stages of H. longicornis. In bold is the standard sequence.

Adult females lay up to ~2,500 eggs, with higher egg counts in bisexual vs. parthenogenetic females (10). The eggs hatch into larvae in late summer-early fall. The larvae crawl onto the grass to quest and attach to passing hosts, feeding on blood for 3-5 days. Afterwards, they drop off the host onto the pasture, where they molt to become a nymph and then become inactive during the winter.

In the spring, the nymphs become active again, aquire a new host, attach and feed for 5-7 days, drop off and molt to adults, which are still relatively small (~2 mm, Figure 1).  Adults attach to a host, feed for 7-14 days by which time they are the size of a pea (10 mm), then drop off and digest the blood as they develop eggs.  The females lay the eggs (completing the life cycle) and die.

The distinct periods of abundance of the different forms (nymphs in spring, adults in summer and larvae in fall) occur in areas with a mild-temperate climate. However, the entire life cycle can be highly clustered with overlapping stages at higher latitudes where the active season is short (11). Furthermore Neilson (1) reports that Tenquist (12) found that in Lismore (a city in northeastern Australia with a humid, subtropical climate), the periods of activity and abundance of each development stage are considerably lengthened, such that nymphs can be found throughout the entire year overlapping with adults as well as larvae in mid-summer into fall, likely because all forms survive the “winter”. Case in point, while in New Zealand the unfed nymph is the primary overwintering stage (5), unfed larvae have been observed to overwinter, and so have unfed adults (13) as well as adults on hosts (7) (Figure 2).

Hosts

Vertebrate hosts used by H. longicornis reflect local availability (14). In New Zealand, they prefer domestic ruminants, such as cattle, goats and sheep, as well as multiple species of domestic deer. Non-ruminant hosts include dogs, horses, hedgehogs, cats, hares, rabbits, pigs and humans. They have also been found on skylarks, ducks, chickens, turkeys, sparrows, pheasants and thrushes, and in New Zealand ground birds, such as the Kiwis and banded rails (15). Larvae and nymphs are more often detected on smaller hosts such as hares or goats, whereas adults are more often found on cattle and sheep (16). Interestingly, H. longicornis were seldom found on rabbits as opposed to hares, possibly because the former are more common in dry shorter grass soils where low humidity is unfavorable to H. longicornis (16). Though broadly generalist when it comes to host selection, as a result of this preference for taller grass and high humidity soils, this species appears more likely to parasitize hosts occurring in these types of environments (such as unkempt fields and paddocks). Like most 3-host ticks H. longicornis spend over 90% of the time away from the livestock, usually in the soil or at the base of plants. This limits the effect of topical livestock insecticides (acaricides) on the local populations of ticks, although they can protect individual animals.

Vector Potential

It is important to distinguish between a vector’s ability to transmit a pathogen in the lab and whether it may actually do so in a field setting (e.g. it may not bite the right hosts, have the right seasonality, etc). It is also important to follow up findings of field infected specimens of H. longicornis (not necessarily infectious) with laboratory assessments of vector competence, however authors have often declared H. longicornis a vector solely based on finding it infected with pathogenic agents in the field in areas experiencing disease outbreaks. Pathogens of human and veterinary medical importance that H. longicornis has clearly been shown capable to transmit or repeatedly found infected with, and the associated parts of the world, are listed in Table 1.

 Table 1 – Pathogens for which H. longicornis is a known vector (both capable of transmitting in the lab and/or frequently found infected with in the field), their known distributions, and name of the disease they cause in the specified hosts.

Pathogen Name of disease Geographical distribution Host species affected Reference1
Transmission experiments + field infected:
Theileria luwenshuni Sheep theileriosis Asia sheep  (17, 18)
Babesia gibsoni Canine babesiosis Asia Dogs  (19)
Babesia ovata Babesiosis Japan cattle (20)
Babesia sp. BQ1 (Lintan strain) Babesiosis China Sheep, goats (21, 22)
SFTSV Severe fever with thrombocytopenia syndrome China/Japan Human, livestock (2, 3)
Field infected only, found frequently:
Theileria orientalis  (T. sergenti) Cattle Theileriosis Asia and Australasia Cattle, Asian buffalo (23)
Anaplasma phagocytophilum2 Anaplasmosis China, Korea Goats, water deer (24, 25)
Anaplasma bovis Anaplasmosis China, Korea cattle (26)
Ehrlichia chaffeensis2 Ehrlichiosis China, Korea cattle (27)
Borrelia burgdorferi sl. China, Korea Goats, cattle (25)
Rickettsia japonica Japanese spotted fever Japan Human (28)
POWV Powassan Russia Humans (29)
HYSV (Huaiyangshan virus hemorrhagic fever) China Humans (30)
1The references listed are either reviews or the latest peer-reviewed publications on the subject
2It is unclear if these pathogens are the same as those occurring in the US, or simply in the same species complex

There are also a few pathogens that have been recovered from H. longicornis, but only rarely, such as Anaplasma ovis, Anaplasma marginale, Anaplasma platys, Ehrlichia ewingii, Ehrlichia canis, Bartonella sp., Rickettsia sibirica, Orientia tsutsugamushi, TBEV and Hepatozoon canis. Critically, H. longicornis is a demonstrated laboratory vector of Theileria uilenbergi, Theileria equi and Babesia bigemina. Finally, a Coxiella-like bacterium thought to be a symbiont is prevalent in H. longicornis (31).

Genetics

H. longicornis has populations that are bisexual (diploid), parthenogenetic (triploid), and sometimes both (aneuploid). Parthenogenetic forms are recorded from Australia, New Zealand, New Caledonia, New Hebrides, Fiji, northern Japan (Hokkaido and northern Honshû) and eastern Russia. Bisexual races are sympatric with parthenogenetic races on southern Honshû and Kyûshû Islands and also occur in Korea and southeastern Russia and China. Diploid and triploid forms are reproductively isolated (32).

H. bispinosa is a bisexual tropical species (Pakistan, India, Nepal, Sri Lanka, Bangladesh) that was introduced into Malaysia. However, the tick occurs only in the peninsular part of the country, not in the insular part. Moreover, Hoogstraal and colleagues (33) claim that H. bispinosa “occurs throughout the peninsula,” meaning the Malay Peninsula, which would include: Peninsular Malaysia, Thailand, and (perhaps) southern Myanmar (formerly Burma).

To our knowledge, populations of H. bispinosa do not currently overlap with the temperate H. longicornis.

Confusion with Haemaphysalis bispinosa Neumann 1897

In 1968, Hoogstraal (10) performed an extensive review resurrecting H. longicornis as a species with a complex reproductive portfolio (bisexual, parthenogenetic, both) and establishing H. bispinosa as a tropical bisexual species. The two species are different morphologically (Table 2) and biologically (10) as well as genetically (34). In the same study Hoogstraal declared that H. neumanni Dönitz was a synonym of H. longicornis  (16).

Table 2. Morphological comparison of the closely related Haemaphysalis longicornis and H. bispinosa, modified from (1).

Haemaphysalis longicornis H. bispinosa
Approximate size (mm)
     Unengorged male
     Unengorged female
.
2.5-3.0
2.6-3.3
.
2.0
2.2
Dental formula
     Female
     Male
.
5/5
3/3
.
4/4
2/2
Coxal spurs Short and triangular Long and pointed
Palpal segment (nymph) No bulge on postero-dorsal margin Bulge on postero-dorsal margin
Spiracular plates (nymph) Dorsal projection No dorsal projection

 Records in the US

A multigenerational infestation was detected in August 2017 in a field and a single sheep in Hunterdon county, NJ, opening the possibility that the species may be established in the US. At the time of this writing in November 2017, we still do not have confirmation of establishment. Actions are being taken to both access the size of the infestation (which may require waiting until the spring) and contain it if the species survives the winter. The species has been intercepted on several occasions on animals entering the US, but has no known established populations in North America. Although several literature sources list it in Hawaii, that seems to stem from the erroneous interpretation of a statement by Hogstraal that a female H. longicornis was intercepted in a quarantine station in Honolulu in 1967 on a “sheep dog” hailing from Australia in transit to Texas (10). Likewise, a specimen of H. longicornis was intercepted on a horse in a quarantine station in Clifton, New Jersey, in 1969 (35).

Literature Cited

  1. F. J. A. Neilson, Massey University, (1980).
  2. Z. Li et al., Ecology of the Tick-Borne Phlebovirus Causing Severe Fever with Thrombocytopenia Syndrome in an Endemic Area of China. PLoS Negl Trop Dis 10, e0004574 (2016).
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  24. J. G. Kang et al., Prevalence of Anaplasma and Bartonella spp. in Ticks Collected from Korean Water Deer (Hydropotes inermis argyropus). Korean J Parasitol 54, 87-91 (2016).
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  28. K. Tabara et al., High incidence of rickettsiosis correlated to prevalence of Rickettsia japonica among Haemaphysalis longicornis tick. J Vet Med Sci 73, 507-510 (2011).
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  32. J. H. Oliver, Jr., K. Tanaka, M. Sawada, Cytogenetics of ticks (Acari: Ixodoidea). 12. Chromosome and hybridization studies of bisexual and parthenogenetic Haemaphysalis longicornis races from Japan and Korea. Chromosoma 42, 269-288 (1973).
  33. H. Hoogstraal, B. L. Lim, G. Anastos, Haemaphysalis (Kaiseriana) bispinosa Neumann (Ixodoidea: Ixodidae): evidence for consideration as an introduced species in the Malay peninsula and Borneo. J Parasitol 55, 1075-1077 (1969).
  34. R. K. Brahma, V. Dixit, A. K. Sangwan, R. Doley, Identification and characterization of Rhipicephalus (Boophilus) microplus and Haemaphysalis bispinosa ticks (Acari: Ixodidae) of northeast India by ITS2 and 16S rDNA sequences and morphological analysis. Exp Appl Acarol 62, 253-265 (2014).
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