TABLE OF CONTENTS
Tick Infestation in Animals: Pathogenesis, Clinical Signs, Treatment & Prevention
Tick infestation is an important ectoparasitic condition in animals that can cause direct skin damage, blood loss, toxicosis, paralysis, and transmission of several infectious diseases. Heavy infestations may lead to significant morbidity and, in severe cases, death. This article covers the pathogenesis, major effects, clinical signs, treatment, and prevention of tick infestation in animals.
Pathogenesis of Tick Infestation
1. Direct Noxious Effect
The attachment of ticks to the host causes skin irritation with subsequent ulceration and secondary infection. Heavy infestations are associated with anaemia, since adult female ticks may imbibe up to 10 mL of blood.
The presence of a large number of ticks may cause annoyance, and animals become anxious and restless, which may result in weight loss and, in severe cases, death. Such a condition is called “tick worry.”
The wounds may attract screw-worm flies and other flies, and myiasis may develop.
2. Transmission of Diseases
Ticks can transmit bacterial, viral, rickettsial, and protozoal diseases, as well as spirochetes. One of the most damaging effects of ticks is their ability to transmit diseases to their hosts.
Some of these diseases are serious and may have fatal consequences. Transovarial transmission from one tick generation to another via the eggs is possible and contributes to the spread of disease. For example, Babesia spp. in cattle are transmitted by Rhipicephalus (Boophilus) ticks.
3. Tick Toxicosis
Tick toxicosis is a general aggravation of the toxic effects of the parasite’s saliva. Tick bite wounds may allow bacteria, especially staphylococci, to enter the circulation, leading to the development of bacteraemia and septicaemia.
The organisms may spread to other organ systems, including the joints and meninges of the brain and spinal cord, producing arthritis and meningitis. Certain toxins have a suppressive effect on animals, and occasionally this may reactivate chronic infections.
Ornithodoros savignyi causes toxicosis in young calves and lambs. Animals show cutaneous oedema, haemorrhage, rapidly progressing weakness, and prostration. Death can occur within 6 hours. Toxicosis may occur in recumbent animals during rest.
4. Tick Paralysis
Many tick species are known to induce tick paralysis in humans, lambs, calves, and a variety of mammals. These ticks are capable of releasing a neurotoxin (e.g., holocyclotoxin secreted by Ixodes holocyclus by specific cells in the salivary glands) into the host, causing a condition associated with progressive, ascending, afebrile, symmetrical paralysis, with the hind legs being affected first, followed by the forelegs.
In severe cases, the paralysis progresses from the hind legs to the forelegs and may eventually involve the muscles of the head and respiratory system. It is associated with the feeding of a female tick, and the first symptoms occur 5–7 days after attachment. The toxin interferes with neuromuscular transmission by inhibiting the release of acetylcholine at the neuromuscular junction. Animals may die.
Paralysis generally improves after prompt removal of the attached tick, although clinical signs may persist or temporarily worsen in some cases, particularly with Ixodes holocyclus.
Ticks such as Ixodes rubicundus, Rhipicephalus evertsi, Dermacentor spp., and Argas persicus can cause paralysis in animals and birds.
Gotch Ear
Infestations with the Gulf Coast tick Amblyomma maculatum, found in states along the Gulf Coast, can damage the cartilage and pinnae of the ears of cattle, resulting in a condition known as Gotch ear. These lesions may become attractive sites for oviposition by the screw-worm fly, Cochliomyia hominivorax.
5. Sweating Sickness
Sweating sickness is an acute, febrile, tick-borne toxicosis characterized by profuse, moist eczema and hyperaemia of the skin and visible mucous membranes. Epiphora, nasal discharge, salivation, and extremely sensitive skin with a sour odour are other typical signs.
Eventually, the skin becomes cracked and predisposed to secondary infections. The course is often acute, and death may occur within a few days. In less acute cases, recovery may occur. Strains of Hyalomma truncatum that produce an epitheliotropic toxin cause sweating sickness in calves.
Clinical Signs
Clinical signs of tick infestation vary depending on the tick species, intensity of infestation, duration of attachment, and effects of tick-borne toxins or pathogens. Infested animals may show irritation, restlessness, skin lesions, anaemia, weakness, and other signs associated with heavy infestation or tick-borne disease.
In sweating sickness caused by toxin-producing strains of Hyalomma truncatum, clinical signs appear after an incubation period of approximately 4–11 days. Generalized hyperaemia with subsequent desquamation of the superficial layers of the mucous membranes of the upper respiratory, gastrointestinal, and external genital tracts may occur, along with profuse moist dermatitis.
Treatment
Ticks must be removed promptly. Antibiotics and anti-inflammatory agents are useful for combating secondary infections. Immune serum may be used.
Modern tick control in small animal practice commonly involves systemic ectoparasiticides such as the isoxazolines, including fluralaner, sarolaner, and afoxolaner, which provide effective control of ticks and are available in various oral and topical formulations.
Other commonly used acaricides include ivermectin, particularly in large-animal practice and for selected parasitic conditions, although its use and efficacy against ticks vary among animal species and tick species.
Topical acaricides such as fipronil, amitraz, permethrin, and pyrethroids may also be used depending on the species.
Prevention & Control
Effective prophylaxis and control of tick infestations require an integrated approach combining regular use of effective acaricides with environmental and management measures.
In small animals, modern acaricides such as fluralaner, sarolaner, and afoxolaner can provide sustained protection against ticks when administered according to the product label. In large animals, acaricides such as amitraz, pyrethroids, ivermectin, and other approved tick-control products may be used.
