Canine Visceral Leishmaniasis: Clinical Signs, Diagnosis, Treatment and Prevention

Canine visceral leishmaniasis (CVL) is one of the most relevant diseases in small animal practice in Brazil. Endemic across much of the country and directly important to public health, it demands careful clinical reasoning from the veterinarian — from recognizing the earliest clinical signs to long-term follow-up. This article reviews, in a practical way, the points that most often arise in everyday practice.

The vector and transmission

CVL is caused by protozoa of the genus Leishmania (in Brazil, mainly Leishmania infantum). Transmission occurs through the bite of infected female sand flies (phlebotomines). The dog is considered an important reservoir in the urban cycle, which makes vector control and the management of positive animals matters of collective — not just individual — health.

Understanding the vector directly guides prevention strategies: sand flies are crepuscular and nocturnal and breed in decomposing organic matter, which links environmental control to patient protection.

Clinical signs

CVL is a systemic disease with variable presentation. Many dogs remain asymptomatic for long periods, while others develop a multisystemic picture. Among the most frequently described clinical signs are:

• Cutaneous lesions: exfoliative (scaling) dermatitis, alopecia — especially periocular ("spectacles") — and ulcers, particularly over bony prominences.
• Lymphadenomegaly: lymph node enlargement, often generalized.
• Onychogryphosis: excessive nail growth, a classic sign that frequently catches the owner's attention.
• Progressive weight loss and muscle atrophy, sometimes with preserved appetite.
• Other findings: ocular lesions, epistaxis, renal changes, and nonspecific signs such as lethargy.

Renal involvement deserves special attention, as it is one of the main causes of morbidity and mortality in these patients and influences prognosis and management.

Diagnosis

Diagnosis combines clinical assessment with serological and parasitological methods. Serological methods (assays detecting antibodies) are widely used in screening and in the epidemiological context. Parasitological and molecular methods — cytology/visualization of the parasite in lymph node, bone marrow or skin aspirates, and techniques such as PCR — allow direct confirmation.

In clinical practice, interpretation should always consider the whole picture: compatible clinical signs, supporting laboratory work-up (complete blood count, biochemistry profile, protein electrophoresis/albumin-globulin ratio, urinalysis with urine protein-creatinine ratio) and the specific tests. A single isolated result rarely tells the whole story.

Clinical staging (LeishVet)

The LeishVet group proposed a widely adopted staging system that classifies dogs into stages based on clinical findings, serology and laboratory parameters (including renal function and proteinuria). This staging guides therapeutic decisions, prognosis and monitoring frequency. Adopting a recognized classification helps standardize management and communicate the case objectively with colleagues and the owner.

Treatment in Brazil and the regulatory context

Treatment of CVL in Brazil is a sensitive and regulated topic. There is a public health dimension because it is a zoonosis, and for that reason the use of drugs in dogs is subject to specific regulation — historically with restrictions on certain substances also used in human treatment. For this reason, it is essential that the veterinarian consult and follow the current regulations of the competent authorities before defining a protocol, avoiding treating any approach as mandatory or permitted without proper, up-to-date verification.

In general, therapeutic management tends to combine authorized leishmanicidal/leishmaniostatic drugs, clinical support (especially renal) and periodic follow-up. Treatment, when indicated, aims at clinical improvement and reduction of parasite burden, but rarely parasitological cure — which reinforces the importance of continuous monitoring and an honest conversation with the owner about expectations.

Prevention

Prevention is perhaps the most impactful chapter for the owner and for collective health. The main strategies include:

• Repellents and collars with insecticide/repellent of proven efficacy against sand flies, reducing the likelihood of a bite.
• Vaccination, according to availability and indication, as a complementary tool — never a substitute — for vector protection measures.
• Environmental control: management of organic matter, yard cleaning, reduction of breeding sites, and caution during peak vector activity hours.

It is the combination of measures, rather than a single isolated intervention, that offers the best protection.

Conclusion

Canine visceral leishmaniasis demands integrated attention from the clinician: recognizing subtle clinical signs, diagnosing with rigor, staging in a recognized way (LeishVet), treating within current regulations and, above all, investing in prevention. As an endemic zoonosis, every decision carries both clinical and public health weight. Documenting each step of follow-up well — especially in long-running chronic cases — is an essential part of responsible, safe care.