Parasite identification is something which vets and veterinary nurses in practice can be heavily involved in, but to do this you need to be confident with recognising them, their lifecycles and the disease processes. This article will hopefully give you a basic overview of the some of the ectoparasites most commonly seen in small animal practice, as well as some tips to help identify individual parasites which work for me and which I have used while training students over the years.
Lice
The three most common lice encountered in small animals are Trichodectes canis and Linognathus setosus in dogs, and Felicola subrostratus in cats (Table 1).
| Trichodectes canis | Linognathus setosus | Felicola subrostratus |
|---|---|---|
| Chewing louse | Sucking louse | Biting louse |
| “T for Trichodectes”: T shaped with a larger head on a smaller body | Has the smallest head: it is a sucking louse so sucks its mouth in | “Felicola fang”: has fangs to bite with as a biting louse |
Trichodectes canis (the dog chewing louse)
Life cycle
The adult female louse lays individual eggs which are known as nits. She “glues” these nits to individual hairs, and these then take five to eight days to hatch. Their life cycle consists of three stages of nymphs which resemble the adults, except for being smaller in size. The third nymph then turns into a sexually mature adult louse. The entire process takes around three to five weeks.
Symptoms
Intense pruritus, scratching and biting at skin are commonly seen clinical signs. When an infestation is present and causing these symptoms, you often see lice moving around in the coat and can, in some cases, see the nits attached to the hairs as tiny white clumps.
The chewing louse can also act as an intermediate host for the tapeworm Dipylidium caninum. So old or debilitated dogs or puppies may have serious complications from a Trichodectes canis burden.
Linognathus setosus
Life cycle
As with other lice, the adult lays eggs known as nits, which are then “glued” to individual hairs. These eggs hatch after two weeks, forming nymphs. The nymphs then go through three further nymph stages before becoming reproductive adults. This total process takes around two weeks.
Symptoms
Clinical signs include pruritus, skin scaling, skin scabs, alopecia and often the appearance of dandruff/dander, which is actually the “nits” attached to the hair shafts.
Felicola subrostratus
Life cycle
Felicola subrostratus eggs hatch after two weeks, and then go through two nymph stages. After these, the louse progresses into a juvenile adult and finally a mature adult. The whole process takes around 30 days.
Symptoms
This chewing louse affects cats, and patients often display variable pruritus, progressive alopecia, skin scaling, matting of coat and erythematous papules.
Mites
The most common mites encountered in small animals are Sarcoptes scabiei, Demodex spp., Neotrombicula autumnalis, Cheyletiella and Otodectes cynotis (Table 2).
| Sarcoptes scabiei | Demodex spp. | Neotrombicula autumnalis | Cheyletiella | Otodectes cynotis |
|---|---|---|---|---|
| “Stumpy Sarcoptes”: have short, stumpy legs | Only become an issue in immuno-compromised patients | Henry harvest mite: commonly found in the Henry’s pocket of the ear in late summer | Triple C: Cheyletiella, claw and comb: have claw-like mouth pieces and comb-type structures on their legs | Hairy: hairs tickle the ear canal where they are commonly found |
Sarcoptes scabiei
Life cycle
Sarcoptes scabiei has four stages in its life cycle: egg, larva, nymph and adult. The adult female lays two to three eggs per day, which is done as they burrow under the skin. These hatch in three to four days. After the eggs hatch, the larvae migrate to the skin surface and create short burrows. The mite at larval stage has only three pairs of legs, and this stage lasts about three to four days. The larvae moult, and the resulting nymphs have four pairs of legs. These nymphs then develop into adult Sarcoptes mites.
Symptoms
The most commonly seen symptom is severe itching, most often on elbows, hocks, ears, armpits, chest and belly, but this can progress to all areas of the body. Infection can occur at the site of intense itching, which can lead to swelling of lymph nodes if untreated. Hair loss at infection sites, often with patches of lost hair and scaling of the underlying skin, is also seen.
It is important to remember that Sarcoptes scabiei is highly contagious between animals and humans.
Demodex spp.
Life cycle
Female Demodex mites lay approximately 20 eggs, which then develop through two six-legged larval stages. Two eight-legged nymph stages follow this, after which they become eight-legged, slender, cigar-shaped adults. All of this occurs in approximately three to four weeks.
Symptoms
Areas of balding skin appear, normally small in size to begin with. Common sites for this balding tend to be around the eyes, face and feet. The skin itself is not itchy; patients only tend to be bothered by the skin condition when a secondary issue develops.
Neotrombicula autumnalis
Life cycle
Neotrombicula autumnalis eggs are laid in soil, where they hatch into six-legged larvae before developing into eight-legged nymphs. At this point, they begin to climb up vegetation waiting for a passing animal to hop on to where they live part of their adult phase. Their whole lifecycle is 50 to 70 days.
Symptoms
The main symptoms are repeated licking, chewing or scratching of affected areas, normally of feet and ears. Mites are normally found between the webs of feet or more commonly in the Henry’s pocket of the ear.
Cheyletiella
Life cycle
Cheyletiella eggs are laid and attached to individual hairs. These then hatch and develop through two larval stages before becoming adults. The entire cycle takes approximately three weeks, and takes place entirely on the host; however, an adult can survive in the environment for up to 10 days.
Symptoms
The most commonly seen symptom is flaky skin – which is what gives it the nickname “walking dandruff” as you can see the mites moving around with bits of skin. Scratching, reddened skin, skin bumps and scabs are also common clinical signs.
Otodectes cynotis
Life cycle
The life cycle of Otodectes cynotis takes three weeks. The females lay around five eggs a day on the surface of the ear canal. Four days later, larvae hatch and become nymphs. There are then two nymphal stages before an adult mite is formed, which then lives for approximately two months.
Symptoms
The main symptoms of Otodectes cynotis infection are shaking and digging at ears, excessive ear wax production and smelly sore ears.
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Dermatology
ISVPS General Practitioner Certificate (GPCert)
May 2026