Ticks are Closer Than You Think: The Spread of Ticks and Tick-Borne Diseases

Faculty's Column (Rikka) July 14, 2025

SATO Megumi Associate Professor, Graduate School of Health Sciences & Research Professor, Institute for Research Administration

Those who walk their dogs or engage in farm work may have encountered ticks. Ticks are external parasites (ectoparasites) that we may encounter in our everyday surroundings.

In 2013, the first human case of Severe Fever with Thrombocytopenia Syndrome (SFTS) was reported in Japan. After this, ticks were widely called “killer ticks” in the media. However, this term is misleading. It is not the tick itself that causes death, but a virus carried by the tick.

SFTS occurs when the virus enters the body through a tick bite and multiplies inside the body. In this way, ticks act as carriers of infection. Ticks can also transmit other diseases, including Japanese spotted fever, caused by Rickettsia, and Lyme disease, caused by Borrelia.

Ticks hatch from eggs as larvae and take a blood meal at this stage. They then molt into nymphs and take a second blood meal. After molting again, they become adults and feed on blood again (Figure 1). Because a single tick feeds on different hosts during its life, it can pick up and pass on infections between animals and humans (zoonotic infection). For this reason, ticks play an important role in spreading infectious diseases.

(Figure 1) The Life Cycle of a Tick

Ticks do not move over long distances on their own. Instead, they are carried by the animals they feed on, which allows them to spread to new areas. As a result, how far ticks travel depends on the types of animals they attach to.

For ticks that carry diseases, important hosts include wild animals such as bears, wild boars, and deer. Different types of ticks prefer different animals, and this can also change as they grow from larvae to adults. In addition, not all ticks can carry the same disease-causing germs—some pathogens can only survive and multiply in specific types of ticks. This is called host (species) specificity.

When the distribution of wild animals changes in a region, the types of ticks present can also change. As a result, the kinds of tick-borne diseases that people need to be aware of may also change.

Furthermore, due to global warming and changes in land use, the distribution of wildlife, including ticks, is changing rapidly, even over just a few years.

Some people try to remove ticks themselves after being bitten. However, this can cause the tick’s mouthparts to remain in the skin, which may lead to prolonged inflammation and increase the risk of infection. While not all ticks carry disease-causing germs, if you are bitten by a tick, it is recommended that you do not remove it yourself but instead visit a dermatologist.

When visiting grassy areas or mountains where ticks are likely to be present, you can reduce the risk of bites by covering exposed skin and by using insect repellent.

Profile

SATO Megumi

Associate Professor, Graduate School of Health Sciences & Research Professor, Institute for Research Administration

Conducts research primarily in Southeast Asian countries, focusing on parasitology (specifically helminths aka multicellular parasites aka parasites that wriggle). Also conducts research on ticks in Niigata to address local issues in the area where my university is located.

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*Article content and profile information are current as of June 2025.