Canine leishmaniasis: The invisible war at dusk🦟

Stages of the disease and clinical signs you should not ignore

Canine leishmaniasis is one of the most complex and treacherous infectious diseases affecting dogs in Mediterranean areas. Its difficulty lies not only in the parasite that causes it, Leishmania infantum, but also in the extraordinary diversity of clinical forms in which it can manifest itself. Epidemiological studies conducted in southern Europe show that between 30 and 60% of dogs exposed to sand flies can become infected, but only 10–20% will develop overt clinical disease during their lifetime, which explains why so many apparently healthy animals are actually silent carriers.

Some dogs live with the parasite for months or even years without showing the slightest symptom, while others develop rapidly progressing and potentially serious skin, joint or kidney problems. For this reason, it is especially important for owners to learn to detect subtle changes in behaviour, weight or skin condition, as the initial signs of leishmaniasis are often subtle but clinically very significant.

Did you know? The sand fly is not ‘just any mosquito’: it does not fly far, but it chooses its location carefully

Unlike many mosquitoes, sand flies tend to travel relatively short distances, which is why two neighbouring houses can have very different risks. Within the same neighbourhood, there may be “hot spots” (damp gardens, cracked walls, dense vegetation) where the risk is multiplied.

Understanding how the disease progresses, what its clinical stages are and what signs should alert us is essential for early diagnosis, appropriate treatment and a significant improvement in the animal’s prognosis and quality of life. In clinical practice, it has been observed that dogs diagnosed in the early stages have a significantly higher average survival rate, with clinical control rates exceeding 80% at five years when follow-up is adequate.

First stop: the subclinical stage, the art of hiding

After the bite of the sand fly—the small mosquito that transmits the disease—the Leishmania infantum parasite enters the body and settles mainly in immune system cells called macrophages. From that moment on, a complex interaction begins between the parasite and the host’s defensive response.

Scientific note: the key is the Th1/Th2 balance

Our immune system does not always respond in the same way. Some lymphocytes, called Th1, activate “direct attack” defences within cells, which helps to stop parasites such as Leishmania. Others, called Th2, produce many antibodies, which are useful against bacteria but less effective against this parasite. In simple terms, it is not enough to have defences; it is crucial that the body uses the right type. 

In the subclinical phase, the dog is infected but shows no visible signs of disease. This stage can last from six months to several years, and various longitudinal studies have shown that more than 70% of seropositive dogs remain asymptomatic for long periods, provided they maintain an effective cellular immune response. In practical terms, this means that a dog may appear completely healthy while the parasite persists in its body.

During this period, the infection can be detected by serological tests, which measure antibody levels, or by PCR, which can identify very small amounts of the parasite’s genetic material. In endemic areas, control programmes recommend at least one test per year, as dogs diagnosed in the subclinical phase have been found to be up to 60% less likely to develop severe kidney damage than those diagnosed in advanced clinical phases.

Furthermore, preventive strategies against sand flies are not merely theoretical: field studies show that regular use of topical repellents or insecticide collars can reduce the risk of infection by 80 to 95%, especially when combined with environmental management measures and reduced night-time exposure.

Your vet advises: the ‘invisible weight’ trick

At Eurovet Veterinary Clinic, we often see that weight loss goes unnoticed because it is slow and gradual. That is why we insist so much on weighing animals regularly as a preventive measure. At Eurovet, weighing is completely free of charge, and we take advantage of the visit to give them a cuddle (and a treat 😉) and record their weight in our database, creating a monthly curve that allows us to detect problems before they become apparent. 

When the balance is broken: initial clinical phase and first warning signs

When the immune system is no longer able to contain the infection, the disease begins to manifest clinically. This initial clinical phase is characterised by non-specific and progressive signs, which are responsible for numerous diagnostic delays.

One of the most common findings is skin involvement, present in up to 90% of dogs with clinical leishmaniasis. Periocular alopecia, scaling and ulcerative lesions on the ears, muzzle or limbs reflect a chronic inflammatory process associated with the multiplication of the parasite in the skin. The persistence of these lesions for weeks or months, even with conventional treatments, should always be considered a warning sign.

In general, clinical studies indicate that more than 60% of affected dogs experience progressive weight loss, while apathy and decreased exercise tolerance appear in one out of every two cases. Intermittent lameness, although less well known, has been described in approximately 20–30% of dogs, associated with joint or muscle inflammatory processes.

At this stage, an accurate diagnosis is crucial. Several studies have shown that starting treatment in the first few months after the onset of clinical signs improves analytical and clinical parameters in more than 70% of patients during the first year of follow-up, while also reducing the risk of progression to irreversible lesions.

The most serious aspect of the disease: advanced stage and systemic involvement

If leishmaniasis is not diagnosed and treated in time, the parasite spreads and causes multisystemic involvement. In this advanced stage, the disease ceases to be primarily a dermatological problem and compromises vital organs.

Chronic renal failure is one of the most serious complications and occurs in up to 40–50% of dogs with advanced leishmaniasis, being the main cause of mortality associated with the disease. Clinical studies show that the onset of persistent proteinuria triples the risk of clinical worsening if adequate treatment and close follow-up are not established.

Generalised lymphadenopathy, hepatomegaly and splenomegaly are also common, as are haematological disorders such as anaemia, which is present in approximately 60% of advanced cases. Onychogryphosis, although not exclusive to leishmaniasis, occurs in a significant percentage of dogs with chronic disease and usually indicates a prolonged course.

Clinical curiosity: the nail that doesn’t fit

Onychogryphosis (nails that grow abnormally and excessively) is very noticeable, but it does not appear “suddenly”. When you see it, it is usually the tip of the iceberg of a chronic process. It is an excellent example for educating the guardian: the body warns of internal problems with visible signs.

At this stage, treatment does not seek to completely eradicate the parasite, but rather to achieve clinical and parasitological control. Clinical data indicate that, with rigorous monitoring and good adherence to treatment, more than 70% of dogs with advanced leishmaniasis can maintain an acceptable quality of life for several years, underscoring the importance of owner commitment and regular veterinary monitoring.

Sources and recommended reading

Solano-Gallego, L., Koutinas, A., Miró, G., Cardoso, L., Pennisi, M. G., Ferrer, L., Bourdeau, P., Oliva, G., Baneth, G. (2011) – Directions for the diagnosis, clinical staging, treatment and prevention of canine leishmaniasis. – Veterinary Parasitology – European consensus document establishing the scientific basis for the diagnosis, clinical classification and therapeutic management of canine leishmaniasis. – https://www.sciencedirect.com/science/article/pii/S0304401711001603

LeishVet Group, Solano-Gallego, L., Miró, G., Koutinas, A., Cardoso, L., Pennisi, M. G., Ferrer, L., Bourdeau, P., Oliva, G., Baneth, G. (2018) – LeishVet guidelines for the practical management of canine leishmaniasis. – Parasites & Vectors – Evidence-based update on the clinical management, monitoring and prevention of canine leishmaniasis in endemic areas. – https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-018-2712-1

ESCCAP Spain (2023) – Control of canine leishmaniasis in endemic areas. – European Scientific Counsel Companion Animal Parasites (ESCCAP) – Practical reference guide for the prevention, screening and epidemiological control of leishmaniasis in dogs. – https://www.esccap.es

MSD Veterinary Manual – Leishmaniasis in dogs. – MSD Veterinary Manual – Clinical reference manual summarising the pathophysiology, clinical signs, diagnosis and treatment of canine leishmaniasis. – https://www.msdvetmanual.com

Brianti, E., Falsone, L., Napoli, E., Gaglio, G., Giannetto, S., Solari Basano, F., Tarallo, V. D., Otranto, D. (2014) – Efficacy of a slow-release imidacloprid (10%)/flumethrin (4.5%) collar for the prevention of canine leishmaniasis. – Parasites & Vectors – Field study demonstrating a reduction of more than 90% in the risk of infection by Leishmania infantum in dogs protected with a slow-release insecticide collar. – https://link.springer.com/article/10.1186/1756-3305-7-327

Fernández-Cotrina, J., Iniesta, V., Belinchón-Lorenzo, S., Muñoz-Madrid, R., Serrano, F., Parejo, J. C., Gómez-Nieto, L. C., Alonso, C. (2018) – A large-scale field randomised trial demonstrates the safety and efficacy of the LetiFend® vaccine against canine leishmaniasis. – Vaccine – Multicentre randomised clinical trial showing a significant reduction in the incidence of clinical leishmaniasis in vaccinated dogs compared to placebo. https://saludanimal.leti.com/fernandez-cotrina-et-al-2018-vaccine-a-large-scale-field-randomized-trial-demonstrates-safety-and-efficacy-of-the-vaccine-letifend-against-canine-leishmaniosis_242877.pdf

e Silva, S. C. P. F., Michalsky, É. M., Dias, E. S., Andrade, H. M., Lage, P. S., Lima, A. C. V. M. R., Fortes-Dias, C. L. (2019) – Effectiveness of the mass use of deltamethrin-impregnated dog collars for the control of canine leishmaniosis. – Preventive Veterinary Medicine – Epidemiological study demonstrating the population impact of the mass use of insecticide collars in reducing new infections in endemic areas. – https://www.sciencedirect.com/science/article/abs/pii/S0167587719302909

Pennisi, M. G., Cardoso, L., Baneth, G., Bourdeau, P., Koutinas, A., Miró, G., Oliva, G., Solano-Gallego, L. (2015) – Leishmaniasis in cats: ABCD guidelines on prevention and management. – Journal of Feline Medicine and Surgery – European guidelines describing the clinical presentation, diagnosis and management of feline leishmaniasis in endemic areas. – https://www.abcdcatsvets.org/guideline-for-feline-leishmaniosis/

Vélez, R., Gállego, M., Molina, R., Montoya, A., Portús, M., Miró, G. (2020) – Evaluation of the immunological and clinical impact of vaccination against canine leishmaniasis. – Parasites & Vectors – Critical analysis evaluating the immunological efficacy of vaccines against Leishmania and their possible effect on the dynamics of asymptomatic carriers. – https://pubmed.ncbi.nlm.nih.gov/32035053/