The Danger of Ticks

The risks of ticks to the health of pets and humans

Ticks are arachnids and as such are related to spiders. Adult ticks have 8 legs unlike adult fleas, which are insects and have 6 legs.  Like fleas, ticks must have blood meals to survive and they feed on many types of animal including humans. Not only is the tick bite annoying but they can also spread diseases which are then carried to animals when they feed. Ticks are important vectors of a number of serious diseases, which in the tropics significantly limits livestock farming.

Ticks have three primary stages of development:  larvae, nymph, and adult. When tick eggs hatch, 6 legged larvae emerge and immediately need to feed to gain strength and to grow and moult to their next stage when they become nymphs. Nymphs have 8 legs and continue to feed and moult to the last stage, which is an adult. Consequently the size of ticks varies depending on the stage of their lifecycle or if they have recently fed. Large nymphs or adult ticks that have fed for several days are full of blood so are large and balloon like.

 

Unfed Fed
Adult female 3mm (sesame seed size)
small, oval, and flat
Fully engorged to about 11mm
balloon-like shape
Adult male Approximately 2.5 mm Take smaller meals
Nymph Around 1.5mm
Larvae (6 legs) About 0.5mm
(size of a poppy seed)

 

Ticks need to feed before they grow or develop to the next stage in their lifecycle. Ticks climb to the tip of blades of grass or the ends of leaves or branches and attach to hosts that brush against them. Ticks satisfy all of their nutritional requirements with a diet of blood. To suck blood from their hosts, they cut a hole in the skin and insert their mouth parts or hypostome. They prevent blood from clotting by excreting an anticoagulant.
Ticks in the United Kingdom can carry a number of infections, causing disease in both pets and humans. Infections reside in the tick’s mouth, anticoagulant, or gut and are transmitted through the tick bite. Infections are harmless to the tick and can be passed from adults to eggs so larvae emerge already infected.

There are two families of ticks that can be found in the United Kingdom:

  1. Argasidae, “soft ticks”, so called because they have a spongy and wrinkled back that extends like a hood concealing their head and mouth parts.
  2. Ixodidae, “hard ticks”, so called because they have a hard plate-like shield covering their backs. Unlike soft ticks, the head and mouth parts can be seen from above because the shield does not cover them. As a hard tick feeds and swells up with blood, the shield on its back appears smaller and more towards its head. It is usually a species of hard tick that is found on domestic pets or people.
There are three particular species of hard tick which are more likely to attach to people and pets in the UK:
  • Ixodes ricinus, also known as the sheep tick, wood tick, deer tick and castor bean tick.
  • Ixodes hexagonus, also called the hedgehog tick.
  • Dermacentor reticulatus, also known as the ornate cow tick or the marsh tick.
However, there are many more species of ticks in Britain and 15 of them have been known to occasionally attach to people. A tick’s natural hosts are wildlife and farm livestock, but ticks cannot distinguish pets and humans from their natural hosts. Thus, pets and humans frequently become incidental hosts.
Animals or humans bitten by ticks in the United Kingdom can become infected with a number of pathogens either singularly or in combination. These include:
Viral infections

UK Tick-borne Viral Infections Humans
Dogs Cats
Tick-borne encephalitis (TBE) Yes Yes
Louping-ill virus (LV) Yes Yes

 

Tick-borne encephalitis (TBE) Initial symptoms in humans are fever, headache, nausea and/or vomiting, and common-cold-like cough and sniffles. After about 8 days of remission, the second phase of the disease occurs when the virus enters the central nervous system. Symptoms include a stiff neck, severe headache with intolerance to light and noise delirium, paralysis, and coma.
Louping-ill virus (LIV) is common in upland areas of the UK but it can occur where Ixodes ricinus (the sheep tick) is common. It is generally known as a disease of sheep but can affect cattle, horses, pigs, dogs, deer, red grouse, other wildlife species, and also humans.

Rickettsia infections

UK Tick-borne Rickettsia Infections Humans Dogs Cats
Q-fever Yes Yes Yes
Anaplasmosis and Ehrlichiosis Yes Yes Yes

 

Rickettsia organisms are intermediates between viruses and bacteria. They live in many arthropod hosts such as fleas, lice, and ticks. Rickettsia are parasites of white blood cells of their animal and human hosts.

Rickettsia disease can be acquired either through the bite of an arthropod or through skin abrasions, e.g. when crushing a tick between fingers. It can also be acquired from the inhalation of dried faeces or arthropods.


Q-fever
 (Coxiella burnetii) Ticks are the vector for Coxiella burnetii but the organism is found in the afterbirth and birth fluids, milk, urine, and faeces of infected livestock. Infection of humans generally occurs by inhalation of coxiella burnetii from air that contains contaminated barnyard dust. However, a bite from an infected tick can also result in clinical disease. The UK is considered to be widely infected with Q-fever.
Humans are often very susceptible to the disease and only a few organisms are required to cause infection. Most patients become ill within 2-3 weeks of exposure. Clinical signs are a flu-like onset with fever and fatigue, progressing to pneumonia, anaemia, hepatitis, and cardiac problems.

Anaplasmosis 
and Ehrlichiosis are diseases where the spectrum of symptoms ranges from asymptomatic to fatal. Wild and domestic livestock are both the reservoir and host.
Anaplasma phagocytophilum causes Tick-borne Fever in cattle and sheep as well as Human Granulocytotropic Anaplasmosis (HGA) and can cause clinical disease in other animals.
Clinical disease usually begins within 1-3 weeks of a tick bite. Early symptoms include flu-like malaise, fever, chills, and muscle pain. More acute symptoms can include vomiting, acute weight loss, abdominal pain, cough, diarrhoea, haemorrhages, and renal failure.
Bacterial Infections

 

UK Tick-borne Bacterial Infections Humans Dogs Cats
Borreliosis (Lyme disease) Yes Yes Yes
Bartonellosis Yes Yes Yes

 

Borreliosis (Lyme disease) In the UK Borreliosis predominantly causes neurological complications.
The incubation period of Borreliosis is generally from 3-32 days after a tick bite. Borreliosis occurs in stages, with remissions and exacerbations, and different clinical manifestations at each stage. The early stages may be mild but the patient may present more severe illness later.
In 50% of humans, early stages of disease presents with a single, expanding (bull’s-eye) rash which may last for weeks. Other early symptoms tend to be flu-like and, during this stage, the Borrelia spreads into other tissues, including the skin, nervous system, heart, and musculoskeletal system.
Late disease presents after several years but in the UK and most of Europe, Lyme arthritis is rare. Lyme borreliosis is seen throughout the UK.

Bartonellosis
 The most common form of Bartonella seen in humans in the UK is Bartonella henselae, considered to be widespread in the cat and dog population. Both the cat flea and ticks are arthropod vectors.
In cases of B. henselae infections, lymph nodes (especially around the head, neck, and upper limbs) may become inflamed. Fever, headache, and loss of appetite may occur. B. henselae is frequently encountered as a concurrent infection in cases of Borreliosis.
The incubation of B. henselae is generally 3-12 days. A lesion may appear at the site of the tick bite, but this may be difficult to identify in cases of Borreliosis when a bull’s eye rash also occurs. After 1-3 weeks lymph node enlargement appears, combined with a low-grade fever.
Protozoa Infections

Babesiosis is caused by protozoa which produce a malaria-like disease in livestock, pets, and humans.
Babesia divergens is the cause of Red Water Fever in cattle due to the appearance of blood in the urine. B. divergens has been implicated as the most common agent of human Babesiosis in Europe.
The manifestations of human Babesiosis can range from asymptomatic to severe illness. For individuals who have had their spleen removed, Babesiosis can be fatal.
Tick control measures

A natural form of tick control is the guinea fowl – a bird that consumes large quantities of ticks. Just 2 birds can clear 2 acres (8,100 m2) in a single year.
A tick must be removed from a host without traumatising it. When removed, it may regurgitate which can increase the dose of infection delivered to the host. Use a good tick remover such as the Tick Key® which quickly removes the tick.
There are currently 5 products that are licensed in the UK for tick control on companion animals:

 

Product Dog Treatment Cat Treatment
Advantix Spot On Yes NO
Frontline Spray & Spot On Yes Yes
Pract-Tick Spot On Yes NO
Promeris Stop On Yes Yes (cat formulation)
Scalibor Collars Yes NO

 

Safety Precautions
All of these products must only be used on healthy animals and under veterinary guidance. Some products that are suitable for use on one type of animal can be harmful to others, causing acute illness and even death. Cats are extremely sensitive to tick and flea products that contain Permethrin and can become fatally poisoned.

 

Summary
  • For detailed information visit the Borreliosis and Associated Diseases Awareness UK website.
  • Use products prescribed by your vet to protect your pet from tick bites and complications.
  • Promptly remove attached ticks with a tick removal tool such as the Tick Key®.
  • If you feel you or your pet have a tick-borne infection, prompt treatment can avoid complications.
David Chamberlain BVetMed., MRCVS.
Veterinary Consultant to PetSafe®

Reference:

Borreliosis and Associated Diseases Awareness UK:  http://www.bada-uk.org/

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