Leptospirosis in Wild Mice: An Ongoing Concern for the Azorean Islands

Research Article

Austin J Vet Sci & Anim Husb. 2023; 10(4): 1129.

Leptospirosis in Wild Mice: An Ongoing Concern for the Azorean Islands

Camarinho R1,2*; Nhampule Y1; Garcia PV1,3; Rodrigues AS1,2

¹Faculty of Sciences and Technology, University of the Azores, Portugal

²IVAR – Instituto de Vulcanologia e Avaliação de Riscos, University of the Azores, Portugal

³CE3C – cE3c, Centre for Ecology, Evolution and Environmental Changes /Azorean Biodiversity Group, University of the Azores, Portugal

*Corresponding author: Camarinho R IVAR – Instituto de Vulcanologia e Avaliação de Riscos, University of the Azores, Rua da Mãe de Deus, Apartado 1422, 9501-801 Ponta Delgada, Açores, Portugal. Tel: +351 296650460; Fax: +351 296650100 Email: ricardo.ad.camarinho@uac.pt

Received: September 21, 2023 Accepted: October 14, 2023 Published: October 21, 2023

Abstract

Background: Leptospirosis is a worldwide zoonotic infectious disease that affects Human and animals worldwide with increased risk in regions with temperate climates. Such is the case of the Azorean islands (a Portuguese archipelago with 9 islands) where this disease is considered endemic. Rodents of these islands have been considered the reservoir species for Leptospira and regulating measurements have been previously developed to control and prevent this disease in the archipelago. This study aims to determine a more recent infection rate of leptospirosis in the house-mouse (Mus musculus).

Methodology & Findings: This retrospective study covering a period of 8 years (2011 to 2018), was performed by live capturing Mus musculus in 6 locations of S. Miguel Island (the most populated island of the archipelago). After euthanasia and necropsy of the mice, kidneys were surgically removed and processed in standard histological routine, and slides were stained with modified Warthin-Starry silver stain for spirochetes and scanned for the presence of Leptospires. It was possible to determine that from the 133 wild mice captured, 89 were positive for leptospirosis, representing a 66.91% infection rate.

Conclusion: This study reveals that leptospirosis still represents an increased risk to Human lives and an uncalculated economical loss to the dairy farms of the Azorean islands.

Keywords: Leptospirosis; Mus musculus; Azores; Histological identification

Introduction

Leptospirosis (also called Weil’s disease, after the person who first described the pathogenic organism in 1886) is a bacterial zoonosis caused by the spirochetes of the genus Leptospira [8]. This disease affects Human and animal populations worldwide, and the infection can occur through direct contact with urine or tissues of infected animals, or indirectly though exposure to infected wet soil or water [14]. In animals, leptospirosis can cause abortion, stillbirth, weakness among neonates, reduced milk production in dairy farm animals, and death. In humans, clinical manifestation of the disease may vary from flu-like symptoms to multiple organ failure and death with some reports of diarrhoea, vomiting, myalgia and kidney failure [14,5]. Certain professions such as abattoir workers, banana cutters, cattle farmers and sewer workers, have increased risk of leptospirosis. Similarly, outdoor activities such as swimming, hunting and fishing, also present higher risk. The occurrence of this disease is strongly influenced by climate, indigenous fauna and agricultural practices [6]. The organism survives well in warm, moist conditions, and hence the disease is endemic to many tropical countries. Such is the case of the Azores: a nine island archipelago located in the North Atlantic Ocean (Figure 1). Around 242.000 people live in these islands, which cover around 2340 km2. On account of the tropical temperate climate, leptospirosis has been a permanent concern and considered an endemic problem [15], particularly in the island of S. Miguel and Terceira (on which around 70% of Azoreans reside), on account of increased cattle infection and several fatal human cases [5,7].

Rodents have previously been established as the main wild reservoirs and carriers of Leptospira [3,11] and although they exist in all Azorean islands, their populations haven’t received enough attention [9]. Nonetheless a survey of Collares-Pereira (1997) determined a very high infection rate (88%) of Leptospira in the house mouse (Mus musculus), with other species of rodents with smaller infection rate [black Rats (Rattus rattus) – 33%; and brown rats (Rattus norvegicus) – 67%]. Facing high infection rates in cattle and loss of human lives, the Azorean Government proposed a project to reduce human cases and reduce infection rates of wild and domestic animals. The proposed actions included a better understanding of the ecology of Leptospirosis and their reservoir species, improvement of farming techniques and infrastructures to ultimately allow a sustained reduction of Leptospirosis. Although the absolute eradication of Leptospirosis is an impossible task [16], proper prevention and control can reduce the infection rates in both humans and domestic animals [12].

The aim of this study was to access the infection rates of Leptospira in the most common house mouse (Mus musculus) for the island of São Miguel.

Material and Methods

Ethical Statements

All procedures were carried out in strict accordance with the European Convention for the Protection of Vertebrate Animals used for Experimental and other Scientific Purposes (ETS 123: directive 2010/63/EU) and the Portuguese Law Decree (DL 113/2012). This study was approved by the University of Azores ethics committee (10/2020).

Source of Specimens

A total of 133 wild Mus musculus were live captured from 2011 to 2018 throughout the Island of S. Miguel in 6 locations [Figure 1: 1- An organic farm from Santo Antonio Village (n=18); 2- Leisure area of Pinhal da Paz (n=26); 3- Leisure areas of Rabo de Peixe Village (n=31); 4- Conventional farm from the city of Lagoa (n=23); 5- Rural areas of Furnas Village (n=18); 6- Rural areas of Ribeira Quente Village (n=17)]. Only wild mice (males and females) with more than 10 grams were selected for this analysis. The selection of locations took in consideration the choice of two different farms, two leisure areas and two villages, and their separate locations in order to maximize the analysed area of S. Miguel.

Citation: Camarinho R, Nhampule Y, Garcia PV, Rodrigues AS. Leptospirosis in Wild Mice: An Ongoing Concern for the Azorean Islands. Austin J Vet Sci & Anim Husb. 2023; 10(4): 1129.