# Hematological Ratios in Leishmania infantum—Seropositive and Seronegative Dogs and Their Distribution Across Clinical Stages

## TL;DR

This study examines blood cell ratios in dogs with and without leishmaniosis to assess inflammation and disease progression.

## Contribution

The study identifies specific hematological ratios that differ between seropositive dogs and controls, and how they change with disease stages.

## Key findings

- NLR and MLR are significantly higher in dogs with leishmaniosis compared to controls.
- Hematological ratios vary across clinical stages of canine leishmaniosis.
- NLR and MLR reflect shifts in leukocyte distribution linked to disease progression.

## Abstract

Canine leishmaniosis is a widespread parasitic disease in dogs that can involve a wide range of clinical signs, from mild illness to severe, life-threatening conditions. Inflammation plays an important role in the progression of this disease, and simple blood tests may help to evaluate its presence and severity. In this study, we compared routine blood cell ratios that reflect inflammation between dogs with and without canine leishmaniosis, as well as among different stages of the disease. Data from more than 600 dogs from veterinary hospitals across Spain were analyzed. Significant differences were observed between healthy dogs and dogs with canine leishmaniosis in blood cell ratios that compare different types of white blood cells. In particular, ratios comparing neutrophils and monocytes with lymphocytes were higher in dogs with the disease, while ratios involving platelets did not show relevant differences. In addition, these blood cell ratios varied depending on how advanced the disease was. These results suggest that simple and inexpensive blood measurements obtained during routine laboratory testing may provide useful information about inflammation and disease progression in dogs with canine leishmaniosis, potentially helping veterinarians in the clinical evaluation and monitoring of affected animals.

The neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), and systemic immune-inflammation index (SII) are derived hematological indices reflecting systemic inflammatory balance in dogs with different serological statuses for canine leishmaniosis (CanL). The aim of this study was to describe and compare hematological ratios (HRs) between dogs seropositive and seronegative for Leishmania infantum and to assess their distribution across LeishVet stages. A retrospective multicenter case–control study was conducted, including 305 seropositive dogs and 305 seronegative controls from referral hospitals in Spain. Hematological data were retrospectively reviewed and analyzed. Significant differences were observed in NLR and MLR between seronegative control dogs and dogs with leishmaniosis, whereas no differences were found for PLR or SII. Median NLR and MLR values were higher in dogs with leishmaniosis compared to controls. In addition, comparisons across LeishVet stages revealed statistically significant differences for all evaluated HRs. These findings indicate that NLR and MLR are increased in dogs with CanL and that HR varies across LeishVet stages, as these indices represent the relative proportions of neutrophils and monocytes in relation to lymphocytes; therefore, changes in their values reflect shifts in leukocyte distribution observed across clinical stages.