Fleas, ticks and other external parasites in dogs

Overview

Fleas and ticks

Fleas are wingless insects 2–6 mm long that move through fur and jump using powerful hind legs. Adults feed on animal blood. Cat fleas, Ctenocephalides felis, can also live on dogs.

Adult ticks have eight legs and spend most of their time in the environment. A blood-fed female can be around 1 cm long. Ixodes ricinus and taiga ticks, Ixodes persulcatus, can share the same habitats.

Other external parasites

The canine sucking louse feeds on blood through the skin. The canine chewing louse feeds on skin debris. A louse's entire four- to six-week life cycle occurs on the dog. Sarcoptic mange mites live in the superficial skin layer and are around 0.2–0.5 mm long.

Causes

Flea eggs fall from the coat

Female cat fleas lay an average of 20 eggs daily on the animal, with a maximum of 40–50. The roughly 0.5 mm eggs fall onto bedding and elsewhere in the home. Another estimate found an average of 27 eggs daily over 50 days. Larvae feed on skin flakes and blood-containing adult flea faeces. They avoid light and can hide in carpet pile or under furniture. The cat flea life cycle usually takes three to eight weeks indoors. Depending on temperature and humidity, it can take as little as 12–14 days or as long as 350 days. Another estimate for egg-to-adult development is 14–140 days.

Movement, warmth and carbon dioxide can trigger adults to emerge from cocoons. Without these stimuli, emergence can be delayed for six months or longer.

Female cat fleas start laying eggs within 24–48 hours of their first blood meal. Fleas pass through three larval stages before pupation. Flea allergy develops when the immune system reacts to saliva introduced by a bite.

A tick's blood meal

Ixodes ricinus larvae feed for around two to three days before returning to the environment to develop into nymphs. Nymphs feed for four to six days. Adult females feed on dogs or other large mammals for around five to 14 days.

Mange mite development in skin

Female sarcoptic mites burrow into the superficial skin layer and lay eggs in tunnels. Egg-to-adult development takes two to three weeks.

Risk factors

Flea risk increases in multi-pet households or premises where fleas can breed. Development can continue through winter in heated homes. Imported dogs or those returning from travel can carry fleas or brown dog ticks. Brown dog ticks can survive indoors.

Sucking and chewing lice can spread through close canine contact or shared brushes and bedding. Dogs can acquire sarcoptic mange from foxes or raccoon dogs, including through their bedding sites.

Ear mites occur at any age but are more common in puppies. They can also pass between dogs and cats through close contact.

Demodex mites usually pass from mother to newborn through skin contact during nursing. Overgrowth in adults can be associated with immunosuppressive disease or medication. Sarcoptic mites can survive off the dog at 10–25 °C with sufficient humidity.

Typical symptoms

Signs vary with the parasite and the dog's skin reaction.

• Fleas can cause intermittent scratching even without flea allergy.
• With flea allergy, itching and lesions often centre on the lower back and tail base.
• Eggs attached to hairs and a matted or unkempt coat can suggest lice.
• Sarcoptic mange can start with severe itching and crusts around ears, muzzle, elbows or hocks.
• Ear mites can cause brown, waxy discharge in one or both ears.
• Cheyletiella mites can cause heavy scaling along the back with little itching.

Ticks are often found on the face, ears, armpits, groin or between toes. A small inflamed lump can remain at a bite site. Without flea allergy, bite-related lesions may centre on the underside and groin. Flea allergy can cause crusted bumps on the backs of the thighs and lower back. Sarcoptic mange can cause scratching before visible lesions appear.

Small bald patches on a young dog's head or front paws can indicate Demodex overgrowth. Localised demodicosis usually causes little itching unless bacterial infection is also present. Dogs irritated by ear mites may scratch until skin breaks.

Complications and consequences

Heavy flea infestation can cause iron-deficiency anaemia, particularly in puppies. Scratched skin can develop bacterial infection. Longstanding flea allergy can thicken skin.

Swallowing an infected flea can transmit flea tapeworm. Ticks can transmit pathogens through saliva during feeding. Anaplasmosis can cause sudden lethargy and fever with lameness or pinpoint haemorrhages.

Findings from a tick study

A study published in 2023 collected 342 ticks from dogs and cats at 10 veterinary clinics in northern Europe. Of these, 289, or 84.5%, were Ixodes ricinus. There were 51 taiga ticks, or 14.9%. At least one investigated pathogen was detected in 59 ticks, or 17% of all samples. Borrelia burgdorferi group bacteria occurred in 36 ticks, or 10.5%. The bacterium causing anaplasmosis occurred in 12, or 3.5%. Borrelia miyamotoi occurred in five, or 1.5%. Babesia venatorum occurred in four, or 1.2%. These figures concern PCR findings in ticks.

Diagnosis at the vet

Examining coat, skin and ears

The vet uses a fine comb to look for adult fleas and flea faeces. Flea allergy investigations assess lesion distribution and previous flea protection. Allergy can be difficult to demonstrate if dogs have licked or bitten fleas out of their coat. Improvement after flea treatment can support suspected allergy.

Attached ticks are often visible, but small larvae and nymphs are harder to spot. A parasite saved in a container can be identified in a laboratory. Several superficial skin scrapings are examined for sarcoptic mites. Scraping sensitivity for these mites may be only 20%. Follicle-dwelling Demodex mites are usually sought with deep skin scrapings. Ear mites are sought using an otoscope or microscopic examination of discharge.

Ear mites can be difficult to detect with purulent ear inflammation. Sarcoptic mite antibodies can first be detected in blood five weeks after infection. In identifying lice, the vet can distinguish narrow-headed sucking lice from broad-headed chewing lice.

Symptoms after a tick bite

For suspected anaplasmosis, the vet considers tick exposure, symptoms and blood findings together. Borrelia antibodies usually appear three to five weeks after infection. A positive antibody result indicates exposure and is interpreted alongside symptoms. For suspected anaplasmosis, two antibody samples taken three to four weeks apart can be compared. Species-targeted PCR can also look for Anaplasma genetic material.

Treatment

Treating fleas on the dog and in the home

The vet prescribes a suitable external parasite medicine when needed. Flea control is planned simultaneously for every household pet. Some products kill adults; others prevent egg or larval development. Cleaning focuses on resting areas, where eggs and larvae are most numerous. Controlling an established infestation usually takes two to three months because developing stages remain in the environment.

Washing blankets reduces developing flea stages indoors. When vacuuming sofas, focus on crevices and under loose cushions to remove eggs. Heavy infestation may need an environmental flea product alongside the animal's treatment.

Removing ticks and treating other parasites

Remove attached ticks immediately to stop continued blood feeding and saliva release. With several ticks present, the vet may recommend a product to kill overlooked individuals. Ear mites can be treated with an ear preparation or another external parasite medicine licensed for that use.

Dogs sharing a household are usually treated simultaneously for sarcoptic mange to interrupt transmission. Wash affected dogs' blankets at 60 °C to prevent mites remaining in bedding from causing reinfection. Localised Demodex overgrowth in puppies can resolve spontaneously within six to eight weeks.

Prevention

Time tick protection according to tick activity where your dog walks. Check the coat after walks even with protection in place. Some products repel ticks before attachment; others kill them only afterwards. Frequent swimming or shampooing can shorten protection from some topical products. Travel protection is selected for the destination's ticks and tick-borne diseases. Long-term flea protection reduces exposure to itch-inducing saliva in allergic dogs.

Important for dog owners

Removing a tick at home

Use fine-tipped tweezers to grasp the tick as close to the skin as possible. Pull steadily straight upwards. Do not squeeze it with your fingers. If identification is needed, save it in a small, tightly sealed container where it will not be crushed. Do not try to remove it with oil or alcohol. Afterwards, wash your hands and the bite site with soap and water.

Safe protection at home

Canine topical products containing permethrin can poison cats. Tell the vet about previous seizures before choosing an isoxazoline product. Isoxazolines have been associated with rare seizures.

Frequently asked questions

How can I distinguish flea faeces from ordinary dirt?

Comb the coat with a fine comb and wipe black specks onto damp white paper. Flea faeces produce a reddish halo because they contain undigested blood. They may be present even without visible live fleas.

What if a tick's mouthparts remain in the skin?

If they do not come out easily with clean tweezers, leave the skin to heal. Mouthparts can cause minor local inflammation. Twisting a tick with tweezers can break off its mouthparts and leave them embedded.

Why do I still find fleas after treatment?

New fleas can emerge from household cocoons and jump onto a treated dog. Individual fleas may be seen for up to eight weeks after treatment starts, sometimes longer. Use a flea comb to monitor whether numbers fall during treatment.

Can canine external parasites make people itch?

Dog lice are host-specific and do not infest people. Fleas can bite people, particularly when many emerge indoors without other hosts nearby. Cheyletiella can also cause a temporary itchy rash in people.

Could my itchy dog have lice rather than fleas?

Lice may be found by parting the often-dense hair behind the ears. Their eggs, or nits, are firmly attached to individual hairs. If a small pale insect is found, microscopy can distinguish chewing lice from other findings.