Oz Virus (Amblyomma Testudinarium): Zoonotic Tick Infection

Oz virus is a novel tick-borne virus that was first isolated in Japan in 2018. It belongs to the genus Thogotovirus in the family Orthomyxoviridae. Oz virus was first detected in Amblyomma testudinarium ticks collected in Ehime prefecture, western Japan. Oz virus can cause lethal infection in suckling mice, indicating its pathogenic potential.

The first human infection with the Oz virus was reported in 2022, in a woman in her 70s from Ibaraki Prefecture, Japan. She was hospitalized with symptoms of fever, fatigue, and pneumonia. An engorged tick was found on her thigh. Unfortunately, she died 26 days after hospitalization due to myocarditis, which is inflammation of the heart muscle. This was the first reported fatality associated with Oz virus infection.

Oz virus appears to be transmitted by tick bites, specifically the tick species A. testudinarium which is found widely in Japan. The natural reservoir of the Oz virus is still unknown. There is currently no vaccine available for the Oz virus. More research is needed to fully understand the symptoms, epidemiology, and risks associated with Oz virus infection in humans.

Oz virus infection is a tick-borne disease, commonly known as the tortoise tick or the Asian tortoise tick, A. testudinarium is a species of hard-bodied tick belonging to the family Ixodidae.

Physical characteristics of A. testudinarium ticks

• Size: A. testudinarium ticks are relatively large compared with the ticks of other species. Adult females can measure about 6 to 8 mm in length, while adult males are slightly smaller, ranging from 4 to 6 mm.
• Coloration: The coloration of A. testudinarium ticks varies between life stages and sexes. The unfed adult females typically have a reddish-brown or dark brown body. As they feed, their color changes to grayish-brown or bluish-gray. Adult males have a dark brown to black body with lighter-colored markings.
• Body shape: These ticks have a distinct body shape. Both males and females have a flat, oval-shaped body when not engorged. As they feed and become engorged with blood, their body expands and becomes more rounded.
• Shield (scutum): Also known as the dorsal shield, the scutum is a prominent characteristic of A. testudinarium ticks. It is located on the dorsal side of the body and covers the anterior part of the tick. The scutum is typically dark brown, and in females, it covers the entire dorsal surface. In males, however, the scutum covers only a portion of the dorsal surface.
• Mouthparts: A. testudinarium ticks have specialized mouthparts for feeding on the blood of their hosts. They possess a hypostome, which is a structure used to anchor themselves into the host's skin while feeding. The hypostome has backward-pointing barbs that help the tick remain securely attached.
• Legs: A. testudinarium ticks have four pairs of legs, making a total of eight legs. Each leg has a joint structure with specialized sensory organs, which help them detect hosts. The legs are typically dark brown or black.
• Gnathosoma: Also known as the capitulum, it is the mouthpart structure located at the front of the tick's body. It contains the mouthparts used for piercing the host's skin and sucking blood. In A. testudinarium ticks, the gnathosoma is relatively large and prominent.
• Spiracles: These are small openings located on the sides of the tick's body that serve as respiratory openings. A. testudinarium ticks have pairs of spiracles on each side, through which they exchange gases with the environment.
• Anal groove: Located on the ventral surface posterior to the spiracular plate, it contains the anus and genital opening. In female A. testudinarium, the anal groove is elongated and extends nearly to the posterior end. In males, the anal groove is more rounded.
• Life stages: Like other ticks, A. testudinarium has immature and adult life stages. The immature stages are larva and nymph, and both require a blood meal before molting to the next stage.

These physical characteristics help distinguish A. testudinarium ticks from other tick species. Identification can be challenging, and it is recommended to consult an expert. 

Geographical distribution of A. testudinarium ticks

A. testudinarium ticks are found in Asia, specifically in Southeast Asia. The countries where these ticks have been reported include:

• Taiwan: A. testudinarium ticks were first detected in Taiwan. They are commonly found in Taiwan, especially in coastal areas.
• South Korea: They have been collected from various parts of South Korea, especially from coastal provinces. They are one of the most common tick species found parasitizing humans in South Korea.
• Japan: They have also been reported across various Japanese islands, such as Honshu, Shikoku, and Kyushu.

Preferred habitats of A. testudinarium ticks

• The preferred habitats of A. testudinarium are coastal areas, beaches, and areas near the sea. They tend to parasitize the reptiles that live in these coastal habitats, especially tortoises.
• They also parasitize other organisms found in coastal areas, including rodents, birds, livestock, and humans. But their main hosts are likely reptiles that live in coastal habitats.
• Coastal vegetation including grasses, shrubs, and bushes on beaches and dunes provide suitable microhabitats for the immature stages of A. testudinarium ticks.

The exact method of virus transmission remains unknown; however, it is suspected that being bitten by virus-carrying hard ticks is a likely cause. Oz virus is a novel thogotovirus that is primarily transmitted through tick bites, especially from Amblyomma testudinarium ticks. It has been found in ticks in Japan and can cause lethal infections in mice.

A recent serosurveillance study conducted on humans and other mammals revealed that the Oz virus may also be naturally infecting humans and other mammals in Japan. The natural host of the Oz virus is still unknown.

The Oz virus infection is a zoonotic disease, meaning it can be transmitted from animals to humans. Zoonotic diseases are caused by harmful germs such as viruses, bacteria, parasites, and fungi. These germs can cause many different types of illnesses in people and are very common, with the majority of infectious diseases in people coming from animals. Therefore, it is important to take precautions when handling or coming into contact with animals, particularly wild animals, to prevent the spread of zoonotic diseases.

As the Oz virus is a novel virus, experts emphasize the need for further research to fully comprehend the symptoms.

Known signs and symptoms of the Oz virus may include:

• Hard tick bites on the body
• Fever
• Fatigue/exhaustion/weakness
• Vomiting
• Loss of appetite
• Joint pain
• Pneumonia
• Myocarditis or inflammation of the heart muscle

The recent fatal case involving the Oz virus indicates that the virus can cause severe symptoms and even death. However, the past detection of the virus in people with antibodies also suggests that some people may develop no or only light symptoms.

Oz virus infection can be diagnosed through serosurveillance, which involves testing for the presence of antibodies against the virus in a person's blood. Additionally, symptoms such as fever, headache, and muscle pain may suggest Oz virus infection. In the case of the deceased woman (the first reported case of Oz virus infection), she was hospitalized and underwent a blood test, which revealed a decrease in platelet levels, liver damage, and acute inflammation. The presence of tick bites was also noted by doctors.

Oz virus is a novel thogotovirus isolated from ticks that causes a lethal infection in mice. To test for the presence of Oz virus antibodies in serum samples, an 80 percent plaque-reduction neutralizing test using the Oz virus can be performed. Additionally, the ELISA protocol can be used to detect Oz virus antibodies in serum samples from wild animals.

Diagnosis of Oz virus infection can be challenging as symptoms such as fever, vomiting, and fatigue are seen with other conditions as well. No specific tests are used to diagnose Oz virus in humans yet. Given that it has only one fatal case, it seems diagnosis may still be an area that needs improvement. More research is likely needed to determine the best ways to diagnose Oz virus infections accurately and quickly.

There is currently no specific treatment for the Oz virus. Current guidelines to treat the Oz virus include the following:

• People who test positive for the Oz virus and have symptoms should rest and take over-the-counter medications to relieve symptoms. Getting plenty of fluids and rest is recommended.
• For most people, the Oz virus will only cause mild illness. But some people are at higher risk of serious complications, including older adults and those with underlying medical conditions. They may need to be monitored more closely.
• Severe cases of the Oz virus may require hospitalization. Patients may need supportive care, such as supplemental oxygen or mechanical ventilation. Experimental treatments are also being studied.
• People who may have been exposed to the Oz virus should monitor for symptoms such as fever, cough, and shortness of breath for at least 14 days. They should call their healthcare provider right away if symptoms develop.
• There are currently no vaccines available to protect against the Oz virus. Clinical trials for potential vaccines are underway.

There is no specific antiviral treatment for the Oz virus at this time. Current management focuses on relieving symptoms, monitoring for complications, and providing supportive care.

Prevention through good hygiene practices and social distancing is key to stopping Oz virus transmission. Steps that can be taken to prevent the Oz virus:

• Proper clothing: People should actively avoid exposing their skin to areas where they may encounter hard ticks. When near bushes, individuals should wear long-sleeved shirts and pants to prevent tick bites, especially during the active seasons from spring to fall. Additionally, the use of bug repellents can provide added protection. If someone is bitten by a tick, they should seek medical attention instead of attempting to remove the tick themselves.
• Practice good hygiene, such as washing hands, frequently: Oz virus spreads through respiratory droplets when an infected person coughs or sneezes. Washing hands with soap and water for at least 20 seconds, especially after going to the bathroom or blowing your nose, coughing or sneezing can help prevent infection.
• Avoid close contact with people who are sick: Oz virus spreads mainly from person to person through respiratory droplets. So, avoiding close contact with people who are sick can help reduce your chances of infection.
• Cover your coughs and sneezes: Cover your mouth and nose with a tissue when you cough or sneeze or use the inside of your elbow. Throw used tissues in the trash and immediately wash your hands with soap and water for at least 20 seconds.
• Clean and disinfect frequently touched surfaces: Oz virus may live on surfaces for several hours. Clean and disinfect frequently touched surfaces such as keyboards, doorknobs, light switches, phones, toilets, and sinks in your home, workplace, school, etc.
• Consider wearing a face mask: Wear a face mask when in close contact with other people, especially those who are sick. A face mask can help prevent respiratory droplets from spreading when someone coughs or sneezes.
• Stay home if you are sick: Avoid public activities and public transportation if you are sick. Stay home unless you need to get medical care. Staying home will prevent the virus from spreading to others.
• Consider getting vaccinated: Getting vaccinated for the Oz virus (when a vaccine becomes available) can help prevent infection. Vaccines help develop immunity without causing illness. There are currently no vaccines available to protect against the Oz virus. Clinical trials for potential vaccines are underway.

Good personal hygiene habits, up-to-date vaccination, and practicing good food safety (clean, separate, cook, and chill) are all important methods for preventing the spread of viruses and infectious diseases including Oz virus.