Ticks are obligate blood-feeding ectoparasites belonging to the class Arachnida. They exhibit morphological and biological differences from insects. Except for the egg stage, ticks must feed on the blood of their hosts during all other developmental stages. Their ability to feed on blood at different life stages forms the basis for their role in transmitting diseases to hosts.

BIOLOGY OF TICKS

Ticks require blood meals during their larval, nymph, and adult stages to fulfill essential physiological functions, including feeding, molting, sperm production, and egg-laying.

The biology of ticks from the families Ixodidae and Argasidae differs significantly. In Ixodidae ticks, the life cycle consists of four stages: egg, larva, nymph, and adult. Both male and female ticks feed on the host’s blood while mating. The female tick engorges on blood within 24-48 hours. Once fully engorged, she detaches from the host and seeks shelter under grass, leaves, or stones to lay her eggs, typically beginning the process within 1-2 days.

The number of eggs laid and the duration of egg-laying depend on factors such as the amount of blood ingested, the tick species, and environmental conditions. In Ixodidae ticks, both females die after laying eggs, and males die after mating. Since Ixodidae ticks are predominantly found in pastures, they are commonly referred to as “pasture ticks.”

Ticks from the Argasidae family are known as soft ticks. Because they are commonly found in human and animal dwellings, they are also referred to as “domiciliary ticks.” This habitat reduces the difficulty of finding a host. Unlike other stages, only the larvae remain on the host until they develop into nymphs. Once they reach the nymph stage, they leave the host and return at night to feed.

Their feeding and engorgement periods are relatively short. During the day, they hide in cracks and crevices within their habitat, emerging at night to feed on their host’s blood. After each mating, the female tick lays between 12 and 70 eggs in cracks and crevices. Unlike Ixodidae ticks, both the mated male and the egg-laying female survive.

Some Diseases Transmitted by Ticks

Tick-borne diseases are also observed in our country, affecting both animals and humans and sometimes leading to fatal outcomes.

Babesiosis

Babesiosis is a protozoal disease transmitted by ticks of the Ixodidae family, with hosts including carnivores, pigs, ruminants, equines, rodents, and humans. Due to its impact on livestock productivity and mortality, the disease holds significant importance in animal husbandry.

The infection is transmitted when an infected tick bites its host, introducing the pathogen through its salivary glands. Clinical signs include high fever, anorexia, anemia, jaundice, and hemoglobinuria. Diagnosis is suggested by clinical signs, particularly in endemic regions.

Hepatozoonosis

Hepatozoonosis is a protozoal disease caused by Hepatozoon canis in our country. Its definitive hosts are dogs and wild carnivores. The brown dog tick, Rhipicephalus sanguineus, serves as the primary vector, though other Ixodidae ticks are also believed to play a role in disease transmission.

Transmission occurs when dogs ingest infected ticks. The pathogen enters the dog’s system when tick eggs are consumed, continuing its development within the host. If another tick feeds on an infected dog, H. canis is transferred to the tick, allowing further transmission. Since the pathogen is not present in the tick’s saliva, the disease is not spread through tick bites.

Clinical signs do not always appear in infected dogs. When present, symptoms may include fever, cachexia, depression, anemia, and ocular and nasal discharge. Affected dogs may also show painful, reluctant movement, enlarged lymph nodes, stiffness in the neck and body, and an overall rigid posture.

Lyme Disease (Borreliosis)

Lyme disease is a spirochetal infection caused by Borrelia burgdorferi and transmitted primarily by ticks of the Ixodes genus. The disease affects humans, dogs, horses, cattle, sheep, and, to a lesser extent, cats. While other ticks, mosquitoes, and deer flies may also carry the pathogen, Ixodes ricinus is considered the most significant vector for human infection.

Migratory birds are known to contribute to the global spread of Lyme disease. One of the earliest clinical signs following a tick bite is a skin lesion called Erythema Chronicum Migrans (ECM).

Other clinical manifestations vary among individuals, with the nervous system, joints, and heart being commonly affected. Diagnosis is based on clinical and epidemiological findings, supported by laboratory tests.

Ehrlichiosis

Ehrlichia is an obligate intracellular rickettsial pathogen. The known species include E. bovis, E. ovis, E. chaffeensis, E. ewingii, and E. canis, all of which are transmitted by Ixodidae ticks.

Of particular veterinary importance, Canine Monocytic Ehrlichiosis (CME) is widespread, especially among dogs and other carnivores in tropical and subtropical regions. The disease occurs when E. canis is transmitted to dogs via Rhipicephalus sanguineus ticks.

CME manifests in three clinical forms: acute, subclinical, and chronic.

• In the acute phase, symptoms include depression, lethargy, anorexia, severe weight loss, fever, ocular and nasal discharge, respiratory distress, lymphadenopathy, edema in the limbs and scrotum, occasional epistaxis, and, rarely, neurological signs. Some dogs recover spontaneously, regaining their normal weight and temperature.

• The subclinical phase may persist for years without noticeable symptoms.

• If left undiagnosed, the disease progresses to the chronic form, which can remain asymptomatic for a long period. However, once the immune system is compromised, clinical signs reappear, often more severe than in the acute phase.

Crimean-Congo Hemorrhagic Fever (CCHF)

Crimean-Congo Hemorrhagic Fever (CCHF) is a highly pathogenic and fatal zoonotic disease caused by viruses belonging to the Nairovirus genus of the Bunyaviridae family. The disease is transmitted by ticks.

CCHF has been reported in various regions worldwide. In Turkey, the first clinical cases were observed in 2002 in the provinces of Tokat and Sivas. According to the Turkish Ministry of Health, 150 human cases and six deaths were recorded that year. The mortality rate has increased over time, with 510 cases and 28 deaths reported in 2007.

The virus can infect many domestic and wild animals, usually causing a mild course of disease in them. Although many bird species are resistant to the virus, they play a crucial role in its transmission.

In both animals and humans, the disease begins after a bite from an infected tick. Due to its tick-borne nature, CCHF is a seasonal disease, with cases peaking in warmer months when tick activity is higher.

Ticks of the Hyalomma genus play a significant role in transmission, though approximately 30 tick species have been reported as potential vectors. In Turkey, Hyalomma marginatum marginatum is responsible for the spread of the disease. These ticks are observed on animals between February and December.

The disease initially presents with fever, headache, fatigue, hypersensitivity, severe pain in the extremities and back, and loss of appetite. Some cases also exhibit vomiting, abdominal pain, or diarrhea. In the early days, petechiae on the face and chest, along with conjunctival redness, are noticeable. Ecchymoses may develop on the trunk and limbs. Other common symptoms include nosebleeds, hematemesis, melena, and hematuria, with occasional vaginal bleeding. Hepatitis is also frequently observed.

Following a tick bite, the incubation period typically ranges from 1 to 3 days, whereas direct contact with infected blood, bodily fluids, or tissues results in an incubation period of 5 to 6 days.

Diagnosis and Control

Diagnosis is based on laboratory methods, including RNA isolation of the pathogen and serological detection of viral antigens and antibodies.

Preventive measures play a crucial role in controlling CCHF. Efforts focus on personal protection and reducing tick populations to prevent outbreaks.

Definitions of Some Terms in the Blog Post

• Hemoglobinuria: The presence of hemoglobin in urine, which is normally found in the blood as a crucial protein for oxygen and carbon dioxide transport but is not typically present in urine.

• Cachexia: Severe weight loss due to a complete disruption of normal nutritional functions.

• Lethargy: A state of extreme weakness in vital functions, characterized by deep and prolonged pathological sleep.

• Anorexia: Loss of appetite.

• Scrotum: The pouch-like structure that houses the testicles.

• Hematemesis: Vomiting of blood.

• Melena: Abnormally dark, tarry stools with a foul odor, usually due to gastrointestinal bleeding.

• Hematuria: The presence of blood in the urine.

This blog post has been verified by Veterinarian YUNUS EMRE AŞICI

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