External parasites of the dog are insects or mites. Microscopic fungi are also the cause of external parasites, in particular ringworm.
Insects
Fleas
The flea is by far the most common external parasite in dogs. About a third of dogs are carriers and all, including dogs living in urban areas, are at risk. In France, the flea most often encountered in dogs is the cat flea (Ctenocephalides felis). The adult is an obligate parasite, i.e. it must necessarily feed on the blood of a host (dog, cat, etc.).
– Infestation: the dog is most often infested by fleas which have developed from eggs disseminated in the environment or, more rarely, by passage from an infested animal (dog, cat, etc.).
– Pathogenic risk: during infestation (or pulicosis), flea bites cause the formation of pimples which are associated with itching of varying intensity; it is also not uncommon for allergic reactions to flea saliva to develop and cause marked itching over a large body surface; this allergic skin condition is called allergic dermatitis or flea-bite hypersensitivity dermatitis (DAPP or DHPP). Fleas can also carry the tapeworm Dipylidium caninum, and the dog becomes infected by ingesting fleas when grooming.
Lice – Parasites
Two species of lice can parasites the dog. These insects live on its skin and in its coat, clinging to the base of the hairs. Eggs (or nits) stuck to the hairs can be observed. Lice infestation (called phthiriasis or phtiriosis) is much rarer than that of fleas and mainly concerns poorly maintained animals, especially in communities (kennels, farms).
– Infestation: the dog can be infested through direct contact with another dog or through contaminated objects (brushes, combs, blankets, etc.). The risk of contagion is high.
– Pathogenic risk: lice infestation is generally asymptomatic in adult dogs or is manifested by discreet clinical signs. Depending on the species, they can cause moderate itching, dull hair and dandruff, or intense itching, hair loss and sometimes anemia during massive infestation.
These two species of lice are very specific to dogs and there is no transmission to humans.
Other parasitic insects of medical importance for the dog include mosquitoes and sandflies (small biting insects morphologically close to mosquitoes). If their direct pathogenic role is generally limited, they can have a major indirect pathogenic role, since they are the potential vectors of internal parasites causing often serious diseases: cardiopulmonary dirofilariasis and cutaneous dirofilariasis for mosquitoes, leishmaniasis for sandflies.
Mites
The most common parasitic mites in dogs are ticks.
Ticks – Parasites
Ticks are large mites that can be seen with the naked eye, even when they are not engorged with blood. Ticks are obligate parasites, with each life cycle stage (larva, nymph and adult) having to feed on the blood of a host. For adult females, the blood meal helps produce the eggs. Once swallowed, they unhook and lay eggs in the external environment.
Ticks can live for several years and are active when the weather conditions (humidity and mild temperatures) are favourable: the peak of activity is generally in spring and autumn.
Many species of ticks are likely to infest dogs, but in France, three species predominate; they have slightly different lifestyles and range:
(“wood tick”): this is the most widespread species in Europe, present on the majority of the territory in France (rare however in the Mediterranean region). It appreciates relatively humid areas with fairly dense vegetation (especially wooded areas).
Dermacentor reticulatus: it is present in abundance on the majority of the territory in France, less frequent in the Mediterranean and mountain regions. It lives preferentially on sparsely wooded land (gardens, meadows, edges of waterways, etc.).
Rhipicephalus sanguineus (“indoor tick”): it is especially abundant in regions with a hot climate (in France, in a large south-eastern area). This tick can complete its entire development cycle indoors, in a kennel or house, and therefore be active all year round.
– Infestation: the dog is infested only by ticks that found in the environment, which can be at the larval, nymph and/or adult stage depending on the species. There is no direct transmission from one animal to another.
– Pathogenic risk: the direct risk linked to ticks is limited; on the other hand, they are of major medical importance in dogs, because they are the potential vector of many canine diseases (bacterial, parasitic and viral), some of which are zoonoses (diseases transmissible from animals to humans).
Chiggers
This small mite (Trombicula autumnalis) is also extremely widespread, especially in gardens, and its larvae are a frequent seasonal parasite of dogs. Its proliferation and activity require mild temperatures and fairly dry weather; infestations therefore occur mainly during summer and early fall (July to October).
– Infestation: the larvae climb on plants and drop on a nearby host. They attach themselves to the skin through their mouthparts and feed on the animal’s blood and tissues for about a week. The areas of thin skin are the preferred locations: spaces between the fingers, ears, folds of the thighs or elbows… Attached in groups, the chiggers form clusters of dots or small characteristic orange crusts.
– Pathogenic risk: infestation by chiggers (trombiculosis) causes intense itching, linked to bites, but sometimes also to hypersensitivity (allergy) to their saliva.
The animal may scratch and lick or nibble frantically for long periods of time in an attempt to relieve itself, a behavior that can subsequently cause lesions and secondary infections.
The other dog parasitoses due to mites that can be mentioned are:
– Sarcoptes scabiei, microscopic mite responsible for scabies of the body or sarcoptic mange: it lodges and multiplies in the thickness of the skin of the animal. This parasitosis is more common in young dogs, hunting dogs, stray dogs and dogs that have been in kennels. Very contagious, it causes intense itching.
Contamination of the owner by his infested dog is not uncommon, causing skin lesions, which generally disappear as soon as the dog and the environment are treated.
– Otodectes cynotis, microscopic mite responsible for ear mites: it develops almost exclusively in the ear canal. Both ears are often affected. This parasitosis is not uncommon and is mainly manifested by a brown-black, thick, often abundant earwax, which can be accompanied by itching. Contagion occurs directly between dogs, but also between dogs and cats.
– Demodex canis, microscopic mite responsible for demodicosis (loss of hair on certain areas of the body): it is normally present in the hair follicles (cavity of the epidermis in which the hair develops) and the sebaceous glands of the dog, but can multiply there abnormally in young dogs or immunocompromised adults, which leads to inflammation, then hair loss and sometimes serious secondary bacterial infections.
– Cheyletiella yasguri, 0.5 mm mite (visible with a magnifying glass) responsible for pseudogalius in dogs: the parasite proliferates on the surface of the dog’s skin. Contamination occurs directly during contact with infected animals, or indirectly because the parasite can survive in the external environment.
This rare parasitosis mainly affects puppies from kennels, and sometimes older dogs. It causes itching (due to the attachment of the parasite to the skin and a possible allergic reaction) and the formation of dandruff. In adult dogs, it is often asymptomatic.
Accidental transmission from the infested dog to the owner is quite common and causes skin lesions, which disappear as soon as the dog and the environment are treated, because the parasite does not survive on humans.
Mushrooms
Ringworm is the main canine external parasitosis caused by fungi. Some breeds, such as terriers, are predisposed. The proliferation of the fungus can cause more or less significant hair loss which results in generally circular and well-defined depilations. However, other clinical forms are possible. Some subjects are healthy carriers, who therefore do not show clinical signs.
– Infestation: Highly contagious, it is transmitted by contact with an infested animal (sick or asymptomatic) or through contaminated objects or the environment.
– Pathogenic risk: Contamination of humans by a nasty animal is very common.
