Canine Leishmaniasis

Leishmaniasis is a disease caused by a protozoan that can infect dogs. It's transmitted through the bite of a sandfly from the genera Phlebotomus (in Eurasia and Africa) and Lutzomyia (in the Americas). It's more common in warm climates, and is widespread in Spain.

It causes a wide range of symptoms and is spreading due to climate change. Luckily, increasingly effective treatments are available to address it. We can also take preventive measures, which will be key. Let's take a detailed look at everything related to leishmaniasis.

What is leishmaniasis?

Leishmaniasis is a parasitic disease caused by protozoa of the genus Leishmania, usually the species infantum. It's an intracellular parasite, since it lives inside macrophages (immune defense cells). It's a worldwide zoonosis in which the main reservoir is the dog. It requires an arthropod vector, such as Phlebotomus sandflies. It's a chronic, lifelong disease.

Found worldwide, it's more present in warm-climate regions such as the Mediterranean, South America, Asia, or Africa. There are several clinical presentations of the disease.

Life cycle of leishmaniasis

Female sandflies of the Phlebotomus genus need certain blood proteins to lay their eggs. So a female already infected with the Leishmania protozoan transmits the parasite to another host through her bite. The parasite is engulfed (absorbed) by the host's macrophages, where it develops. If not destroyed by the macrophage, the parasite usually spreads. Another female sandfly, when biting this infected host, picks up the parasite, which develops in her digestive tract so it can be transmitted again.

Epidemiology

In Spain, prevalence is very high, and as for breeds, all can be affected except the Ibizan Hound, which over time has been found to have developed immunity and resistance. It will affect individuals with a weaker or compromised immune system more.

This arthropod's optimal temperature is 17 to 30ºC, with humidity of 60 to 100%. They need decomposing organic matter in their environment. Peak activity occurs during low-light hours, at dawn and dusk.

Symptoms

Depending on the antibody titer and parasite load involved, symptoms can range from none at all to severe clinical presentations. Symptoms can be systemic/general or cutaneous.

1. Systemic or general: weight loss, muscle wasting, pale mucous membranes, epistaxis (nosebleeds), anemia.
2. Kidney changes: glomerulonephritis, kidney failure, elevated urea and creatinine, proteinuria (protein in urine).
3. Liver changes: granulomatous hepatitis, elevated transaminases (liver enzymes).
4. Digestive changes: ascites, granulomatous ulcerative colitis, large-bowel diarrhea with or without blood.
5. Musculoskeletal changes: intermittent limping, polyarthritis from deposition of Leishmania immune complexes...
6. Eye changes: conjunctivitis, keratitis, blepharitis, uveitis...
7. Cutaneous: a lesion at the bite site, possibly appearing twenty days after the bite, usually in hairless areas. Nasal or paw pad hyperkeratosis (dry skin) can occur.

We may see wounds and ulcers that become painfully chronic on the edges of the ears, between the toes (paw pads), etc. We may also notice single or multiple nodules.

Diagnosing leishmaniasis

The first thing the vet will do is take a history and do a general physical exam. Full bloodwork can be run to see the animal's overall systemic condition. At the clinic, a "Snap" test can be run on a blood sample from the animal. If positive, the dog very likely has Leishmania.

Next, a serum sample from the patient needs to be sent to a lab to determine their antibody titer. This gives us an idea of the parasite load they've developed — the higher the titer, the greater the load.

To physically look for the parasite, the vet can take a bone marrow and lymph node sample (where the highest number of macrophages are found) for cytology. A smear of the sample is prepared, and the parasite is looked for inside the macrophages. A skin biopsy can be done if nodules are present.

Treatment Depending on the antibody titer, treatment and dosage will be set up. Generally, Glucantime (meglumine antimoniate) is used for a month to a month and a half, given daily as a subcutaneous injection, plus allopurinol. Glucantime can cause acute kidney failure — if this happens, it should be stopped, or if the dog already had kidney issues, its use will be assessed. Oral miltefosine plus allopurinol can also be used. In addition, any systemic symptoms present need to be treated with the appropriate treatment. The animal should be reassessed every three to six months.

Prevention

In hosts — that is, in our dog — two types of immune response can occur against Leishmania parasitism:

• Humoral response: mediated by B lymphocytes, this always occurs starting one and a half to three months after infection, but these antibodies aren't effective (they work against extracellular pathogens). They don't provide protection, and they form immune complexes that can cause problems.
• Cellular response: mediated by T lymphocytes, macrophages are activated, allowing them to kill off the parasite. This strong response occurs in resistant dogs, such as the Ibizan Hound mentioned above.

Knowing this, we can test our dog for Leishmania using a snap test that tells us whether they have Leishmania or not from a blood sample. If negative, vaccination can proceed.

This vaccine helps ensure that, if the animal becomes infected, they have a better chance of developing a Th1 cellular response. If bitten by a sandfly carrying Leishmania, what the vaccine does is make sure that if any parasite remains in the macrophages, it's such a small amount that no clinical symptoms develop.

So, if you want to avoid lifelong Leishmania infection, especially in areas with high sandfly prevalence, testing and vaccination should be done yearly. On the other hand, to prevent sandfly bites, preventive anti-parasite measures can be used. For example, the Scalibor collar prevents sandfly bites for up to twelve months. Spot-on treatments or screens/mosquito nets can also help.