Evaluation of the House Fly Musca domestica as a Mechanical Vector for an Anthrax

et al. (2010) Evaluation of the House Fly Musca domestica as a Mechanical Vector for an Anthrax. PLoS ONE 5(8): e12219. doi:10.1371/journal.pone.0012219 Evaluation of the House Fly Musca domestica as a Mechanical Vector for an Anthrax Antonio Fasanella 0 Silvia Scasciamacchia 0 Giuliano Garofolo 0 Annunziata Giangaspero 0 Elvira Tarsitano 0 Rosanna Adone 0 Frank R. DeLeo, National Institute of Allergy and Infectious Diseases, National Institutes of Health, United States of America 0 1 Istituto Zooprofilattico Sperimentale of Puglia and Basilicata, Anthrax Reference Institute , Foggia , Italy , 2 Faculty of Agriculture, University of Foggia , Foggia , Italy , 3 Department of Public Health and Animal Sciences, Faculty of Veterinary Medicine, University of Bari , Valenzano (Bari) , Italy , 4 Istituto Superiore di Sanita` , Roma , Italy Anthrax is a disease of human beings and animals caused by the encapsulated, spore-forming, Bacillus anthracis. The potential role of insects in the spread of B. anthracis to humans and domestic animals during an anthrax outbreak has been confirmed by many studies. Among insect vectors, the house fly Musca domestica is considered a potential agent for disease transmission. In this study, laboratory-bred specimens of Musca domestica were infected by feeding on anthrax-infected rabbit carcass or anthrax contaminated blood, and the presence of anthrax spores in their spots (faeces and vomitus) was microbiologically monitored. It was also evaluated if the anthrax spores were able to germinate and replicate in the gut content of insects. These results confirmed the role of insects in spreading anthrax infection. This role, although not major, given the huge size of fly populations often associated with anthrax epidemics in domestic animals, cannot be neglected from an epidemiological point of view and suggest that fly control should be considered as part of anthrax control programs. - Funding: Founds Ministry of Health of Italy: Ricerca corrente 2008. Title of the research: Modello sperimentale per la valutazione di Musca domestica come potenziale vettore di Bacillus anthracis. Code: IZSPB 004/08 RC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Anthrax is a human and animal disease caused by the encapsulated, large rod, and spore-forming Bacillus anthracis. The bacteria grow vegetatively within body tissues of the host, with sporulation occurring when vegetative organisms are exposed to the atmosphere. Animal anthrax primarily affects herbivore ruminants, such as cattle, sheep, and goats, which are the most susceptible animal hosts. The disease occurs following ingestion of soil-borne anthrax spores. Human anthrax usually results from a cutaneous infection caused from the handling of infected animal products or, in rare cases, by ingesting or inhaling spores from contaminated animal products [1]. Anthrax spores may spread within a geographic region through water, insects, wild animals, birds, and contamination from body fluids of infected animals [2,3]. The potential role of insects in the spread of B. anthracis to humans and domestic animals during an anthrax outbreak has been confirmed in many studies [4]. Tabanids as well as Stomoxys calcitrans, Musca domestica, and Calliphora erythrocephala have been evaluated as transmitting agents [5,6]. The house fly, Musca domestica, has long been considered as a potential agent for disease transmission, and bacteria have been isolated from feces, vomitus, external surfaces, and internal organs of this species [5,7]. Structurally, the fly is well adapted for collecting pathogens. Its proboscis has a profusion of fine hairs that readily collect environmental detritus. The ability of the fly to carry anthrax bacilli from anthrax-infected flesh to wounds of healthy guinea pigs has also been demonstrated [8]. However, little quantitative information regarding the spread of anthrax cells by flies exists. In Italy, anthrax is normally a sporadic disease [9,10]. In 2004, there was an anthrax outbreak in the Basilicata region in southern Italy, which previously had a low prevalence of anthrax. The outbreak involved a large number of animals within a large geographic area and occurred with the span of a few weeks. In total, the epidemic killed 124 animals of different species [11]. Owing to the unusual characteristics of this epidemic, some risk factors were evaluated such as the possible transmission by insect vectors [12]. The infection evolved in different phases, and flies, whether necrophilic or hematophagic, were believed to have had a role in spreading the infection. During the first phase of this epidemic, the anthrax-infected carcasses of cattle were exposed to wild carnivores (wild boars) and insects for several days. Insects had prolonged access to the infected carcasse (...truncated)