Haemaphysalis is a diverse genus of hard-bodied ticks with numerous species found across various continents. These external parasites have distinctive physical characteristics and feed on a wide array of animal hosts. Haemaphysalis ticks are significant due to their widespread presence and their potential role in transmitting various pathogens.
Identifying Haemaphysalis Ticks
Identifying Haemaphysalis ticks relies on specific morphological features. A distinguishing characteristic of this genus is the shape of their mouthparts, specifically the second segment of the palps. These segments flare outwards laterally, extending beyond the basis capituli, creating a bell-like appearance. This feature helps differentiate them from other common tick genera.
The size of Haemaphysalis ticks varies depending on their life stage and whether they have fed. Unfed adult females of Haemaphysalis longicornis typically measure between 2.0 to 2.6 millimeters in length and 1.5 to 1.8 millimeters in width. After a blood meal, an engorged female can expand significantly, reaching up to 9.8 millimeters long and 8.2 millimeters wide. While their coloration can range from light to dark brown, it is not a reliable feature for species identification, as color can vary even within the same species.
H. longicornis has a notable capacity for parthenogenesis, a form of asexual reproduction where females can lay fertile eggs without needing a male. This allows a single engorged female to rapidly expand a new population. Parthenogenetic populations of H. longicornis are prevalent in the Asia-Pacific region and have successfully established themselves in new territories, including the United States.
Global Distribution and Habitat
The Haemaphysalis genus is broadly distributed, with native populations spanning across Asia, Europe, Africa, and Australia. For instance, Haemaphysalis concinna is widespread throughout Eurasia, including Russia and China. Haemaphysalis punctata, also known as the red sheep tick, is found from southwestern Asia into much of Europe. This wide native range highlights the genus’s adaptability to diverse climates and ecological conditions.
A significant aspect of their global presence involves the invasive spread of Haemaphysalis longicornis, often referred to as the Asian longhorned tick. Native to temperate regions of East and Central Asia, including China, Korea, and Japan, it also has established populations on Pacific islands such as Australia, New Zealand, Fiji, and Hawaii. The tick was first confirmed in the mainland United States in Hunterdon County, New Jersey, in November 2017.
Since its initial detection, H. longicornis has rapidly expanded its geographical footprint across North America. It has been reported in at least 20 states, primarily concentrated in the eastern and southeastern regions of the United States. This includes states such as New York, Pennsylvania, Maryland, Virginia, West Virginia, North Carolina, South Carolina, Arkansas, Connecticut, and Ohio. Its ability to establish viable populations in these new areas is a growing concern for public and animal health officials.
Haemaphysalis ticks commonly inhabit wooded areas, grasslands, and regions characterized by dense undergrowth, where host animals frequently roam. H. longicornis, for example, prefers warm, moist conditions and has been observed in various settings, including unmowed grass, forest edges, and within forested areas.
Common Host Animals
Haemaphysalis ticks exhibit a broad host range, feeding on a diverse array of vertebrate animals across their life stages. This adaptability to different hosts contributes to their widespread distribution and ability to thrive in various ecosystems. Hosts are broadly categorized into wildlife, livestock, and domestic animals.
Wildlife hosts include large and medium-sized mammals such as white-tailed deer, opossums, raccoons, and wild pigs. Smaller wild animals like rabbits, hares, ground-nesting birds, rodents (including mice and rats), coyotes, foxes, badgers, and even bears also serve as hosts. Haemaphysalis leporispalustris is commonly known as the rabbit tick due to its strong association with lagomorphs.
Livestock animals are frequently parasitized by Haemaphysalis ticks, making them significant agricultural pests in many regions. Cattle, sheep, goats, horses, donkeys, and pigs are common hosts. Heavy infestations on livestock, particularly by H. longicornis, can result in considerable blood loss, leading to anemia and, in severe cases, even death, impacting agricultural economies.
Domestic animals, including dogs and cats, are also susceptible to Haemaphysalis tick bites. While humans are not considered primary hosts, they can be bitten, especially when spending time in areas with high tick populations such as tall grass or wooded environments. The wide range of available hosts facilitates the tick’s life cycle and its potential spread to new areas.
Associated Pathogens and Diseases
Haemaphysalis ticks are competent vectors for various pathogens, causing diseases of medical and veterinary importance. The specific pathogens transmitted can vary by tick species and geographic location, underscoring the regional risks associated with these parasites. These ticks transmit viruses, bacteria, and protozoa.
Among viruses, Severe Fever with Thrombocytopenia Syndrome Virus (SFTSV) is a significant concern, primarily transmitted by H. longicornis in East Asia. This bandavirus causes a severe febrile illness characterized by fever, fatigue, headaches, and a reduction in blood platelet count (thrombocytopenia). Case fatality rates for SFTSV have been reported between 6.2% and 32.5% in countries like China, Japan, and South Korea.
Heartland virus (HRTV) is another viral pathogen vectored by Haemaphysalis ticks, first identified in Missouri in the United States. While the lone star tick (Amblyomma americanum) is the primary vector, H. longicornis has been confirmed to transmit this virus, which causes flu-like symptoms, leukopenia, and thrombocytopenia. Other viruses, such as Russian spring-summer encephalitis virus, Powassan virus, and Crimean-Congo hemorrhagic fever virus, have also been associated with various Haemaphysalis species.
Bacterial infections transmitted by Haemaphysalis ticks include anaplasmosis, caused by Anaplasma species. These bacteria infect white blood cells, leading to symptoms like fever, lethargy, and muscle aches. Rickettsial diseases, including Japanese spotted fever and other spotted fever group rickettsioses, are also transmitted. For example, H. concinna can transmit Rickettsia heilongjiangensis, and Rickettsia rickettsii has been found in H. leporispalustris.
Haemaphysalis ticks can also transmit Borrelia species, which cause Lyme disease, Ehrlichia chaffeensis, and Francisella tularensis, the causative agent of tularemia. Protozoal diseases are also a concern, particularly theileriosis in cattle, caused by Theileria orientalis (genotype Ikeda). This disease can lead to significant economic losses in livestock due to anemia, decreased milk production, and even mortality. Babesia species, which cause babesiosis in animals like dogs (Babesia gibsoni) and livestock (Babesia major, Babesia motasi), are also transmitted by Haemaphysalis ticks.