# Copy numbers of the S-adenosylmethionine synthetase (METK) gene in 14 dogs with active Leishmania infantum infection

## TL;DR

This study examines the copy numbers of the METK gene in dogs with active Leishmania infantum infection to understand allopurinol resistance and its clinical implications.

## Contribution

The study investigates the clinical relevance of METK gene copy numbers in dogs with Leishmania infantum, linking them to allopurinol resistance and disease relapse.

## Key findings

- Most dogs with clinical suspicion of resistance had METK gene copy numbers below 3.0.
- All dogs showed clinicopathological signs of active leishmaniasis.
- Resistant strains may be transmitted by sand flies, highlighting the zoonotic risk.

## Abstract

Relapses of canine leishmaniasis during allopurinol treatment are common and complicate the course of disease. S-adenosylmethionine synthetase (METK) gene copy numbers (CN) < 3.0 have been demonstrated in allopurinol-resistant Leishmania infantum strains in vitro, but its clinical impact in vivo is still unclear. This study included 14 dogs divided into two cohorts (C): Cohort one (CI): nine dogs (64%) with signs of disease relapse under allopurinol treatment; Cohort two (CII): five dogs (36%) recently diagnosed with active leishmaniasis prior to treatment. Leishmania infantum infection was confirmed by positive PCR testing. METK gene CN was quantified by droplet digital PCR. Complete blood counts and biochemical profiles were performed where suitable samples were available. METK gene CN ranged from 0.7 to 3.4 [CN < 3.0 (n = 13), 93%; CN = 3.4 (n = 1), 7%; CI: CN = 1.2–3.4; CII: CN < 2.0 each]. Clinicopathological abnormalities consistent with active leishmaniasis were observed in all dogs. Allopurinol is used for long-term management of canine leishmaniasis, therefore identification of resistance to allopurinol is crucial, especially in cases of clinical relapses. Leishmaniasis poses a zoonotic risk to humans so that the spread of parasites due to resistance should be considered regarding the One Health aspect and the All Species approach. In dogs recently diagnosed with active leishmaniasis not receiving allopurinol yet, resistant L. infantum strains may most likely be transmitted by sand flies. The threshold of METK gene CN < 3.0 in vivo seems to be questionable in individual cases.

Image 1

•METK gene CN < 3.4 recorded in 9 dogs with clinical suspicion of resistance.•METK gene CN < 3.0 recorded in 8 of the 9 dogs with clinical suspicion of resistance.•METK gene CN < 2.0 recorded in 5 dogs prior to receiving allopurinol.•Considering allopurinol resistance is crucial for further therapeutic management.•Identifying dogs with resistance is crucial to avoid the spread of resistant strains.

METK gene CN < 3.4 recorded in 9 dogs with clinical suspicion of resistance.

METK gene CN < 3.0 recorded in 8 of the 9 dogs with clinical suspicion of resistance.

METK gene CN < 2.0 recorded in 5 dogs prior to receiving allopurinol.

Considering allopurinol resistance is crucial for further therapeutic management.

Identifying dogs with resistance is crucial to avoid the spread of resistant strains.