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Tiks as carriers of diseases

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Tuesday, 30 de November 1999
Author: Pedro Fabrica - Médico Veterinário

Tiks as carriers of diseases

There are  about 800 tick species all over the world (although only a few are commonly encountered in domestic animals) and this number tends to proliferate with the increase in numbers of their preferred hosts (especially abandoned dogs and cats). It is an ectoparasite that needs 1, 2 or 3 hosts (animals from which the ticks feed to reproduce themselves and to survive), depending on the tick species. Ticks, being vectors and reservoirs of many organisms pathogenic not only for animals but also for humans, represent a danger for the public health, and the owners of domestic animals, namely dogs and cats (but not limited to), must not neglet an adequate prevention.

How does the tick lives?

We can divide ticks in two categories, according to their basic morphologic characteristics:

1. Hard-shelled ticks - which cuticle (or "shell") is hard;
2. the soft-shelled ticks - which cuticle (or "shell") is soft; this type of ticks is usually found in the animals’ ears, grooves on the ground and on walls and in other habitats with stable environmental conditions.

Ticks can infest a very extensive range of animals: wild and domestic ruminants, horses, pigs, dogs, cats, rodents, birds, lagomorpha, etc., feeding from their blood. Depending on the species, some ticks only attach to a host during their life cycle, while others can attach to two or three different hosts, during their life cycle.

Ticks go through four life stages during their life cycle: the egg, the larva, the nymph and the adult. They can infest a host in any of  these stages. An adult can lay a batch of 2000 to 20000 eggs, which will be deposited in the soil, preferably in humid areas of low or medium vegetation.

This means that the "green fields" are a splendid trap for hosts such as grazing ruminants, dogs and cats (Readers surely noticed that whenever their dogs go to the country and roam in the fields or walk in that beautifully kept garden, they return with a tick in the ears or in the paws...). Some tick species can lay eggs twice a year, while others will only be "mothers" on their third year of life. Adult ticks are more active in Spring and in Autumn.

Ticks prefer different hosts (and different parts of their hosts’ bodies) according to their species. For instance, the Ixodes scapularis prefers reptiles and rodents while  the Amblyoma americanum is the most aggressive species for the humans and their domestic animals. The species commonest encountered is the Rhipicephalus sanguineus (brown tick), that generally infects the ears, neck and fingers of the dogs.

What diseases can ticks transmit to animals?

Certain ticks, through neurotoxins present in their saliva, can produce ascending paralysis in their hosts. This situation is usually solved by removing the whole tick of the host, ensuring that no traces of the tick’s  "mouth" are left in the animal’s skin. Using ether (preferably), or alcohol on the parasite it will become “lethargic” and easy to remove by forcing it  to do a "somersault”.

Ticks can bear a microbe (protozoa - microscopic unicellular beings) type, that will be transmitted to animals when they are bitten by the tick. These protozoa will "colonize" the red globules and/or the mononuclear cells of the host provoking a disease which takes 1-3 weeks to incubate.
The following are most prominent protozoa and the diseases than can be transmitted by the ticks: Rickettsia conorii (Boutonneuse Fever), Coxielia burnetti (Q Fever), Borrelia burgdorferi (Lyme disease or Borreliosis), Hepatozoon canis (Hepatozoonosis only in puppies, immunosurpressed animals and animals with concurrent disease such as Ehrlichiosis and Babesiosis) Ehrlichia spp (Ehrlichiosis) and the Babesia canis (Babesiosis).

Not all the dogs or cats infected by these protozoa will show signs of disease; however, those that become sick will present the following symptoms: fever, depression, lethargy, nasal and/or ocular discharge, weight loss, lameness, pale mucous membranes, coughing, breathing difficulties, vomiting, diarrhea, bloody urine (type "Port Wine"), neurological disturbances, paralysis of front legs, hemorrhage through the nostrils (epistaxis), shock and even death if they aren’t immediately treated.

Therefore, whenever you find a tick in your pet stay alert in the course of the following 1-3 weeks. Some animals develop a chronic disease which diagnosis is very difficult because the signs are subclinical; however the severity of this type of disease is slightly inferior.

What type of diseases can the ticks transmit to humans?

The famous "tick fever “or “hays fever “are simply infections caused by the protozoa which are transmitted to humans when they are bitten by a tick. The incubation period depends on type of the protozoa and it may vary from 3 to 30 days without symptoms.

For instance, in Ricardo Jorge's fever (or botonosa mediterranian fever or spotted Mediterranean fever) it begins with a primary wound (a small red ulcer covered by a black "punctuation") were the tick has bitten the skin; three to seven days later the person has the following symptoms: fever, headaches, pain in muscles or joints, or swollen lymphatic ganglions; the skin shows a widespread rash, firstly macular and later maculopapular; the mortality is low.

Humans infected by the above mentioned protozoa may show the following symptoms:  fever, headaches, rash, myalgias, signs of insecto bite, nausea and vomiting, abdominal pain, conjunctivitis, swollen lymphatic ganglions, diarrhoea, balance loss, altered mental state, arthritis, jaundice. etc. Therefore, you must avoid the direct contact of the skin with the ticks and in case of any doubts consult your family doctor.

How to avoid the ticks and diseases they can transmit?

There are countless ectoparasite products in the market, although not all of them have proved to be effective. For a really effective control animals should use a collar with a product composed of  amitraz (which, however, may be toxic for humans and young, senior or sick pets) or based on fipronil or permethrin (sprays or "spot on" - pipettes or tubes that are applied in the back of the animal in one or two places unreachable by it).

Usually these products have a minimum effectiveness of 4 weeks on the ticks, as well as on fleas, lice and some skin acarids. Baths with insecticide shampoo are not advisable, because they can cause skin irritation, peeling and intoxication of the animal; on the other hand, its effectiveness is usually limited to maximum two/three days after the bath. The use of insecticide powders is also not advisable, due to the danger of intoxication caused by the easy access and ingestion by the pets. When used, owners should make sure that their pets will not have access to these products.

Regarding infections by protozoa, there are two types of vaccines that are effective: one for the Lyme disease, which is highly effective, and one for Babesiose, which may be 70% to 100% effective in endemic areas. Finally, there is a composed protozoaricide that can be preventively administered the seasons of bigger infection risk (Spring and Summer).


As we have seen, the prevention is the strongest weapon than the pet owners can use to control tick infestations and the diseases they transmit. In case of doubt, never hesitate and consult your vet.

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