Ticks have the potential to pose public health and biosecurity risks because they can carry and transmit human and animal diseases. However, the Ministry is not aware of any cases of people catching a disease from a tick bite in New Zealand. The main diseases of concern in some other countries are not currently present in New Zealand.
Ticks are parasites that require blood for subsistence and reproduction. They feed off a range of hosts including mammals, reptiles, birds and amphibians.
Types of ticks
There are 2 types of ticks – hard ticks (Ixodids) and soft ticks (Argasids). Hard ticks are more readily identifiable than soft ticks and also spend more time attached to their hosts than soft ticks, who feed for a short period of time.
New Zealand has endemic ticks (i.e., they occur here and nowhere else in the world). These species are host-specific and infest mainly birds. Endemic New Zealand ticks generally do not transmit diseases to humans.
There is also an introduced species of tick in New Zealand – the brown cattle tick (Haemaphysalis longicornis), which can infest warm-blooded mammals (such as cattle or humans). In some parts of the world the cattle tick is known as vector of animal and human diseases, such as tick borne fever, Japanese (Oriental) spotted fever, Russian spring-summer encephalitis. However, these diseases are not present in New Zealand.
The ticks present in New Zealand have shown the ability to transmit pathogens, such as bacteria and viruses. Fortunately, the pathogens are rare in New Zealand and damage is mainly isolated to economic loss caused by heavy infestations. However, since travellers could introduce tick-borne diseases to New Zealand, there is a risk (albeit a very low one) that the ticks currently present in New Zealand could spread introduced diseases.
Where are ticks found?
Hard ticks favour habitats with areas of vegetation, such as forests and fields, where females lay eggs on the ground. They may also be found in urban areas if there are unoccupied patches of grass.
Soft ticks generally favour sheltered habitats and will hide in the nests of hosts.
How ticks feed
Ticks are known for latching onto their hosts and feeding off them, resulting in a wound.
Both sexes feed on blood, but only the female becomes greatly distended during engorgement.
Often the larval stage, the nymph stage, and adults seek new hosts after they molted on the ground.
Health risks from ticks
Diseases from ticks
During the feeding process ticks extract the blood of their host and regurgitate excess water from the blood back into the wound. This process enables diseases to be transmitted between a tick and its host.
In some countries ticks have transmitted diseases such as:
- Theileriosis, caused by a protozoan pathogen (Theileria sp.)
- Lyme disease, caused by Borrelia bacteria, and
- Spotted fever, caused by Ricketsia bacteria.
Transmission of disease does not occur immediately, usually the infected tick does not begin to transfer diseases until it has been attached and fed for 24 hours or more.
The Ministry reiterates that these diseases are NOT actually present in New Zealand at the current time.
Additionally, the one strain of Theliria (T. orientalis) found in New Zealand has not been shown to be pathogenic in humans.
The risk of getting a disease from a tick bite in New Zealand is therefore very low, but there is the potential for this to change – for example, if disease carrying ticks arrive on travelers to New Zealand who have been in countries where they are present.
The bite wound from the tick is not generally painful, however some people may experience itching and redness around the area.
Treatments for tick bites vary. If the tick is still attached to a person’s skin, it should be removed immediately. The area where the tick has bitten should then be cleaned and disinfected. If symptoms persist, a health professional should be consulted.
It is important to be aware that ticks carry a range of diseases and may transmit these when biting. Consult a health professional if a person develops flu-like symptoms or the area becomes infected.
It is helpful to keep removed ticks for identification purposes as different species transmit different diseases.
The following precautions may be taken to prevent being bitten.
- Cover up when stationary, particularly ankles and feet.
- Apply an insect repellent regularly when in outdoor areas (those containing diethyl toulamide or dimethyl phthalate as the active ingredients are the most effective).
- Avoid walking in dense vegetation – keep to tracks and cleared areas.