Leishmaniasis in dogs – symptoms, tests and treatment

Overview

Leishmania infantum is the most common cause of canine leishmaniasis in Europe. The disease is particularly associated with the Mediterranean region. Imported dogs and travel also bring infections into areas without ongoing transmission. Suitable sandfly vectors are thought to be absent from some parts of northern Europe.

Infection and clinical disease are different: a dog can carry the parasite without symptoms or routine laboratory changes. An estimated 10% of infected dogs show clinical signs. Infection can still become active later.

In endemic areas, infection is typically identified in 5–30% of dogs. Where infection pressure is particularly high, the proportion may exceed 60%. These figures describe infection rather than only visibly ill dogs.

Causes

Sandflies transfer the parasite into the skin

The usual transmission route is the bite of a blood-feeding female sandfly, which deposits parasites in the skin. The parasite enters macrophages, the body's scavenger cells, and multiplies inside them. From the skin, parasites can spread through lymphatic vessels and blood to other organs.

They are found in sites including lymph nodes, the spleen, liver and bone marrow. Strong cell-mediated immunity can keep infection controlled for a long time. However, high antibody production does not necessarily protect against disease progression.

Infection can also spread without an insect

Infection can pass from a dam to puppies before birth. Blood transfusion from an infected dog can also transmit the parasite to the recipient. Sexual transmission has additionally been demonstrated.

Transmission through bite or wound contact is considered possible, but evidence for this route is uncertain.

Risk factors

Risk increases when a dog lives in or visits a sandfly-transmission area without effective bite protection. Dogs living outdoors or used for hunting have greater exposure in such areas. The background of a dog adopted from an endemic area also affects the possibility of infection.

Concurrent diseases, poor nutrition and immunosuppressive treatment can promote clinical disease. Breed and inherited characteristics may also influence whether symptoms develop. Predisposition to disease has been described in German Shepherd Dogs, Rottweilers, Cocker Spaniels and Boxers.

Sandflies seek hosts mainly after sunset, so the time spent outdoors affects exposure.

Typical symptoms

Signs may begin around 3 months or several years after infection. The first change may be a small bump or ulcer at the bite site on an ear flap, muzzle or abdomen. This local bite lesion usually lasts several weeks and can disappear on its own.

• Skin becomes scaly, hair thins or poorly healing ulcers form.

• Skin changes particularly affect the face, ears and limbs.

• Nails may grow unusually long and become misshapen.

• Your dog loses weight, becomes tired and has less stamina.

• Lymph nodes enlarge and oral mucous membranes may look pale.

• Eyes or eyelids become inflamed, and dry eyes can also develop.

• Thirst and urination may increase because of kidney changes.

• Signs may include nosebleeds, vomiting, diarrhoea or lameness.

Extensive skin changes are not usually itchy, so an absence of itching does not rule out infection.

Ulcers or nodules may also form on oral, nasal and genital mucous membranes. Muscle wasting can alter appearance as well as ordinary weight loss.

Complications and consequences

Immune complexes accumulating in the kidney's filtering structures can trigger inflammation and gradually cause kidney failure. Kidney changes may already be present before visible symptoms develop. Severe chronic kidney disease is a major cause of death in leishmaniasis.

Immune complexes can also accumulate in blood vessels and joints. Joint, bone or muscle inflammation may explain lameness. Very severe disease can involve pulmonary thromboembolism or end-stage kidney disease.

The outlook for mild clinical stage I disease is generally good. In moderate stage II disease, it ranges from good to guarded. In severe stage III, it is guarded to poor. In very severe stage IV, it is poor.

Diagnosis at the vet

Infection is demonstrated and the cause of signs investigated

Investigations include a detailed travel and health history and a full physical examination. A blood count, blood biochemistry and urinalysis assess the infection's effects on the body. The blood count may show anaemia, a shortage of red blood cells.

Blood globulins may increase markedly and albumin decrease. Kidney damage is assessed using the urine protein-to-creatinine ratio, or UPC. Clinical staging applies to dogs with symptoms or laboratory evidence of disease, rather than symptom-free infection alone.

The renal profile for mild stage I disease includes UPC below 0.5 without abnormal kidney blood values. UPC above 1 may be associated with glomerular damage in severe stage III.

Examination may also identify an enlarged liver or spleen. Platelet numbers or function may be abnormal. Other concurrent vector-borne infections are investigated where needed because they can cause similar signs.

Quantitative antibody testing, such as ELISA or IFAT, measures the strength of the immune response against the parasite. Antibodies may only appear around 3–5 months after infection. In a symptom-free infection, their development may be delayed for years.

Sample selection affects test sensitivity

PCR looks for parasite genetic material in samples such as skin lesions, lymph nodes or bone marrow. Blood and urine PCR detect infection less reliably than testing suitable target tissue. Cytology may also show parasites directly inside macrophages.

A sample may contain too few parasites to detect even when the dog is clearly ill. PCR alone is not recommended for screening a dog without symptoms that has not been vaccinated. Even confirmed infection may coexist with another disease causing the signs.

For a more detailed diagnosis, testing samples from 2–3 different tissues is generally recommended. Special tissue staining may help confirm parasites difficult to see on routine microscopy. Previous leishmaniasis vaccination is considered because some vaccines can induce cross-reacting antibodies in antibody tests.

Treatment

Medication depends on disease severity and kidney condition

The vet plans treatment according to clinical stage and kidney disease. Common combinations are allopurinol with miltefosine or allopurinol with meglumine antimoniate. Individual supportive care and a diet suitable for the dog's health are also needed.

Condition may begin improving within a few weeks, but clinical recovery usually takes months. Medication does not usually eliminate every parasite, so a dog that seems well may remain a carrier. Infection can relapse after treatment. Most allopurinol-treated dogs have achieved clinical recovery within around 6–12 months.

Allopurinol can cause urinary xanthine crystals or stones. Kidney mineralisation is another adverse effect. Monitoring uses urine samples and abdominal ultrasound where needed.

Miltefosine may reduce appetite or cause vomiting and diarrhoea. Meglumine antimoniate can irritate the injection site and damage kidneys. Evidence on treatment options and clinical outcomes for mild stage I disease remains limited.

Pancreatitis has also been described as a rare adverse effect of meglumine antimoniate. Allopurinol disrupts parasite RNA and protein production. Domperidone may be used as an immune-modulating adjunct. However, more research is needed on the effectiveness of immune-modulating treatments.

Follow-up continues after visible signs disappear

Baseline checks for an infected dog without symptoms are recommended around every 3–6 months. Antibody levels may decrease within 6–12 months in some treated dogs. A renewed rise alongside symptoms may indicate reactivation.

The first comprehensive reassessment of a treated, clinically ill dog is recommended after the first treatment month. During the first year, investigations usually continue every 3–4 months. In a clinically recovered dog, the interval may later extend to 6–12 months.

Prevention

Sandfly bites are prevented with a suitable repellent parasite-control product throughout exposure. An infected dog also needs protection so parasites do not pass to new sandflies. A product's effectiveness against sandflies must be checked specifically.

In risk areas, keep your dog indoors from dusk until dawn, when sandflies are most active. Fine mesh over windows and doors may reduce insect entry. In the Mediterranean, transmission usually runs from April to November, but year-round protection may be needed in warmer areas.

Vaccination can reduce the risk of clinical disease but does not prevent infection itself. An infected dog is not used for breeding or blood donation. After travel, quantitative antibody testing is recommended around 6 months after the last exposure.

Screening dogs without symptoms also includes assessing infection before leishmaniasis vaccination or blood donation.

Do not use canine products containing permethrin on cats because it is poisonous to them.

Important for dog owners

Keep details of origin country, travel, tests and previous medication, including records from years ago. Tell the vet about new skin changes, weight loss, nosebleeds or increased drinking. Attend agreed urine and blood checks even when your dog is bright. Before travel, ask about sandfly protection suitable for the destination and ensure carers understand the products used. Agree beforehand what to do about adverse effects or recurrent signs.

Leishmaniasis is a zoonosis, an infection that also affects people. Breaking the insect-mediated transmission cycle is central to preventing human infection. A good treatment response does not remove the dog's possible role as a parasite source for sandflies.

Other household dogs' infection status is investigated separately where necessary.

Frequently asked questions

Can a dog develop leishmaniasis only after returning home?

Yes: months or years may pass between infection and symptoms. Becoming ill after returning home therefore does not mean infection was acquired locally. A latent parasitic infection can reactivate. Investigations also consider travel from years earlier.

Does a negative test rule out infection?

Not definitively: antibodies may develop only 3–5 months after infection, or later in a dog without symptoms. PCR sensitivity also depends on the sample. PCR alone is not recommended for screening a healthy dog. Quantitative antibody testing can complement PCR when screening a dog without symptoms.

Can leishmaniasis be cured permanently?

Treatment can restore good clinical health without eliminating every parasite. Relapse is common. Assessment therefore includes laboratory monitoring alongside symptoms; healed skin alone does not show the infection has ended.

Does vaccination replace sandfly control?

No: vaccination reduces the risk of disease developing but does not prevent infection. Repellent parasite protection remains part of prevention for vaccinated dogs too. Exposure is considered throughout travel or the local sandfly season. Infection status is investigated before vaccination is considered.

Why are urine samples needed when signs affect the skin?

Leishmaniasis can damage kidneys before visible renal symptoms develop. The urine protein-to-creatinine ratio helps assess kidney damage severity. Allopurinol can also cause urinary crystals and stones that need monitoring. Abdominal ultrasound may form part of follow-up too.