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Stomoxys flies are mechanical vectors of pathogens present in the blood and skin of their animal hosts, especially livestock, but occasionally humans. In livestock, their direct effects are disturbance, skin lesions, reduction of food intake, stress, blood loss, and a global immunosuppressive effect. They also induce the gathering of animals for mutual protection; meanwhile they favor development of pathogens in the hosts and their transmission. Their indirect effect is the mechanical transmission of pathogens. In case of interrupted feeding, Stomoxys can re-start their blood meal on another host. When injecting saliva prior to blood-sucking, they can inoculate some infected blood remaining on their mouthparts. Beside this immediate transmission, it was observed that Stomoxys may keep some blood in their crop, which offers a friendly environment for pathogens that could be regurgitated during the next blood meal; thus a delayed transmission by Stomoxys seems possible. Such a mechanism has a considerable epidemiological impact since it allows inter-herd transmission of pathogens. Equine infectious anemia, African swine fever, West Nile, and Rift Valley viruses are known to be transmitted by Stomoxys, while others are suspected. Rickettsia (Anaplasma, Coxiella), other bacteria and parasites (Trypanosoma spp., Besnoitia spp.) are also transmitted by Stomoxys. Finally, Stomoxys was also found to act as an intermediate host of the helminth Habronema microstoma and may be involved in the transmission of some Onchocerca and Dirofilaria species. Being cosmopolite, Stomoxys calcitrans might have a worldwide and greater impact than previously thought on animal and human pathogen transmission. Les stomoxes sont des vecteurs mécaniques de pathogènes présents dans le sang et les tissus cutanés de leurs hôtes, spécialement le bétail, mais aussi parfois les humains. Pour le bétail, leurs effets directs sont principalement la perturbation des animaux, les lésions de la peau, la réduction de l’alimentation, le stress, la spoliation sanguine et un effet immunosuppressif global. Ils entrainent aussi le regroupement des animaux pour une protection mutuelle ; tout cela favorise le développement des parasites chez les hôtes et leur transmission. Leur effet indirect est la transmission mécanique de pathogènes. En cas de repas interrompu, les stomoxes peuvent reprendre leur repas de sang sur un autre hôte. En injectant de la salive avant l’absorption de sang, ils peuvent inoculer du sang infecté qui restait sur leurs pièces buccales. En plus de cette transmission immédiate, il a été observé que les stomoxes pouvaient conserver du sang dans leur jabot, qui offre un meilleur environnement pour les pathogènes. Ces derniers peuvent être régurgités lors du prochain repas de sang. Ainsi, une transmission retardée semble possible par les stomoxes. Un tel mécanisme a une conséquence épidémiologique considérable, puisqu’il permet une transmission de pathogènes entre les troupeaux. Les virus de l’anémie infectieuse équine, de la fièvre porcine africaine, des fièvres à West Nile ou de la Vallée du Rift, sont connus pour être transmis par des stomoxes ; d’autres sont suspectés. Des rickettsies (Anaplasma, Coxiella), d’autres bactéries et des parasites (Trypanosoma spp., Besnoitia spp.) sont aussi transmis par les stomoxes. Enfin, les stomoxes sont aussi des hôtes intermédiaires de l’helminthe Habronema microstoma et pourraient être impliqués dans la transmission de certaines espèces d’Onchocerca et de Dirofilaria. En étant cosmopolite, Stomoxys calcitrans pourrait avoir un impact plus important qu’initialement imaginé sur la transmission de pathogènes aux animaux et aux humains.

Background Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a recently emerged coronavirus that is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic. COVID-19 in humans is characterized by a wide range of symptoms that range from asymptomatic to mild or severe illness including death. SARS-CoV-2 is highly contagious and is transmitted via the oral–nasal route through droplets and aerosols, or through contact with contaminated fomites. House flies are known to transmit bacterial, parasitic and viral diseases to humans and animals as mechanical vectors. Previous studies have shown that house flies can mechanically transmit coronaviruses, such as turkey coronavirus; however, the house fly’s role in SARS-CoV-2 transmission has not yet been explored. The goal of this work was to investigate the potential of house flies to mechanically transmit SARS-CoV-2. For this purpose, it was determined whether house flies can acquire SARS-CoV-2, harbor live virus and mechanically transmit the virus to naive substrates and surfaces. Methods Two independent studies were performed to address the study objectives. In the first study, house flies were tested for infectivity after exposure to SARS-CoV-2-spiked medium or milk. In the second study, environmental samples were tested for infectivity after contact with SARS-CoV-2-exposed flies. During both studies, samples were collected at various time points post-exposure and evaluated by SARS-CoV-2-specific RT-qPCR and virus isolation. Results All flies exposed to SARS-CoV-2-spiked media or milk substrates were positive for viral RNA at 4 h and 24 h post-exposure. Infectious virus was isolated only from the flies exposed to virus-spiked milk but not from those exposed to virus-spiked medium. Moreover, viral RNA was detected in environmental samples after contact with SARS-CoV-2 exposed flies, although no infectious virus was recovered from these samples. Conclusions Under laboratory conditions, house flies acquired and harbored infectious SARS-CoV-2 for up to 24 h post-exposure. In addition, house flies were able to mechanically transmit SARS-CoV-2 genomic RNA to the surrounding environment up to 24 h post-exposure. Further studies are warranted to determine if house fly transmission occurs naturally and the potential public health implications of such events. Graphical abstract

Insects are efficient vectors of bacteria and in the hospital environment may have a role in spreading nosocomial infections. This study sampled the flying insect populations of seven hospitals in the United Kingdom and characterized the associated culturome of Diptera, including the antibiotic resistance profile of bacterial isolates. Flying insects were collected in seven U.K. hospitals between the period March 2010 to August 2011. The bacteria carried by Diptera were isolated using culture-based techniques, identified and characterized by antimicrobial susceptibility testing. A total of 19,937 individual insects were collected with Diptera being the most abundant (73.6% of the total), followed by Hemiptera (13.9%), Hymenoptera (4.7%), Lepidoptera (2.9%), and Coleoptera (2%). From Diptera, 82 bacterial strains were identified. The majority of bacteria belonged to the Enterobacteriaceae (42%), followed by Bacillus spp. (24%) and Staphylococcus spp. (19%). Less abundant were bacteria of the genus Clostridium (6%), Streptococcus (5%), and Micrococcus (2%). A total of 68 bacterial strains were characterized for their antibiotic resistance profile; 52.9% demonstrated a resistant phenotype to at least one class of antibiotic. Staphylococcus spp. represented the highest proportion of resistant strains (83.3%), followed by Bacillus spp. (60%) and Enterobacteriaceae (31.3%). Diptera were the predominant flying insects present in the U.K. hospital environments sampled and found to harbor a variety of opportunistic human pathogens with associated antimicrobial resistance profiles. Given the ability of flies to act as mechanical vectors of bacteria, they present a potential to contribute to persistence and spread of antimicrobial-resistant pathogenic bacteria in the hospital environment.

Background Synanthropic filth flies thrive in human and animal habitats, posing health risks through the transmission of infectious agents. They breed on organic waste, including animal feces, making them carriers of various pathogens. In Egypt, where livestock farming is common and poor sanitation, these flies may contribute to zoonotic disease transmission. The current study investigates parasitic infections in filth flies from three livestock farms in Assiut Governorate, Upper Egypt, highlighting their role as vectors for zoonotic infections, particularly Cryptosporidium , via morphological and molecular tools. Methods A total of 12,749 flies were collected from the study sites via sweep nets. After taxonomic identification, the flies were examined microscopically for parasites using various concentration and staining techniques. Positive samples were further confirmed for infections, particularly for Cryptosporidium parasites, via nested PCR and sequence analysis targeting the COWP and SSU rRNA genes. Results This study revealed the presence of several fly species from seven dipteran families, particularly the family Muscidae, primarily Musca domestica , which presented a high parasite infestation rate of 96.6%. This study revealed a high prevalence of various protozoans and helminths in the collected flies . Cryptosporidium was the most prevalent parasite (64.4–100%), infecting all fly species. Entamoeba and Balantidium were also significant, especially in M. domestica (22.6–90.1%, 8.9–100%), Fannia canicularis (10.5–74.4%, 44.2–88.2%), and Borborillus vitripennis (11.1–50%, 37.2–91.4%). Giardia, Trichuris, and Trichostrongylidae had low to moderate prevalence in multiple fly species . Mites are commonly detected on fly exoskeletons, with high infestation rates observed in Musca domestica (77–100%) and Physiphora alceae (66.7–100%). The present study also reported sporadic infections with Trichomonas , Toxocara vitulorum , and pseudoscorpions, along with notable midge larval infestations (52.1%), mainly at site B. Parasitic infections were highest in autumn and spring, with the lowest rates in winter. Molecular identification confirmed the presence of the zoonotic species Cryptosporidium parvum and Cladotanytarsus gedanicus . Conclusion This study revealed that zoonotic parasites exist in flies and pose potential risks when they are found near humans. Cryptosporidium parvum is the prevalent parasite causing diarrhea outbreaks in animals. This is the first genetic evidence of Cladotanytarsus gedanicus midge from Upper Egypt.

Flies are known to be mechanical vectors of bacterial, viral, and parasitic diseases. Although flies are known to transmit disease, the effects of cleaning behavior have not been well studied. This study quantified the cleaning effectiveness and behavior of three fly species: Sarcophaga bullata, Musca domestica L., and Drosophila virilis. Flies were transferred to plates of Escherichia coli or Pseudomonas aeruginosa and allowed to walk on the bacteria for a total of 5 min. After the flies were contaminated, they were either immediately collected to quantify bacteria or were placed onto sterile plates to clean for 5 or 10 min. After cleaning, flies were placed into tubes with 1 ml of sterile 0.85% saline and were gently shaken for 1 min to remove bacteria. A serial dilution was made and 50-μl spot titers were plated. Cleaning behavior was also monitored and scored for a period of 5 min. Results demonstrate a bacterial reduction for both bacteria on all three fly species. Sarcophaga bullata and D. virilis both showed a significant reduction of both bacteria within 10 min, whereas M. domestica only showed a significant reduction in P. aeruginosa. Cleaning behavior increased significantly in flies that were exposed to bacteria compared to flies that were not exposed to bacteria. This study is important, as it demonstrates that fly cleaning could affect mechanical transmission of disease, and additional studies should look at flies' abilities to remove other types of microorganisms.

House flies (Musca domestica) are often present in swine farms worldwide. These flies utilize animal secretions and waste as a food source. House flies may harbor and transport microbes and pathogens acting as mechanical vectors for diseases. Senecavirus A (SVA) infection in pigs occurs via oronasal route, and animals shed high virus titers to the environment. Additionally, SVA possesses increased environmental resistance. Due to these reasons, we investigated the tenacity of SVA in house flies. Five groups of flies, each composed of ten females and ten males, were exposed to SVA, titer of 109.3 tissue culture infectious dose (TCID50/mL). Groups of male and female flies were collected at 0, 6, 12, 24, and 48 h post-exposure. For comparison purposes, groups of flies were exposed to Swinepox virus (SwPV). Infectious SVA was identified in all tested groups. Successful isolation of SVA demonstrated the titers varied between 106.8 and 102.8 TCID50/mL in female groups and varied from 105.85 to 103.8 TCID50/mL in male groups. In contrast, infectious SwPV was only detected in the female group at 6 h. The significant SVA infectious titer for prolonged periods of time, up to 48 h, indicates a potential role of flies in SVA transmission.

Background Equine hepacivirus (EqHV) from the Flaviviridae family, has been detected in horses worldwide with a global RNA prevalence of up to 7.9%. While vertical transmission and iatrogenic transmission with infected blood products have been demonstrated for this virus, field infection rates suggest an additional horizontal transmission route. The aim of this study was to investigate the potential role of Stomoxys calcitrans (Diptera, Muscidae) – a hematophagous fly that is found in stables with ruminants and horses as preferred hosts– in the transmission of EqHV RNA. Materials and methods From 2021 to 2022, S. calcitrans were collected from three horse barns in eastern Austria. The abdomen of each fly was separated from the head and thorax. The heads and thoraxes, including wings and legs were subsequently pooled, with a maximum of five flies per pool, and assayed for the presence of EqHV using a one-step RT-qPCR. For all positive pools, the corresponding abdomens were analysed individually using the same EqHV one-step RT-qPCR. Results A total of 783 S. calcitrans were collected at the three locations. EqHV RNA was detected in 7/136 pools of heads and thoraxes, including wings and legs, in 2021 and in 7/53 pools in 2022. Most positive pools were detected in autumn. The Ct values of the RT-qPCR were close to the presumed limit of detection. Additionally, EqHV RNA could be detected in 34 of 40 abdomens from 2021 to 20 of 40 abdomens from 2022, validating the results of the positively tested head/thorax pools. The minimum infection rate (MIR) was 1.2% in 2021 and 3.9% in 2022. The maximum likelihood estimation (MLE) was 1.2% in 2021 and 3.9% in 2022. Conclusion Although the amounts of viral RNA were close to the limit of detection, the positive abdomens confirmed an up-take of virus-contaminated blood by the flies, and viral RNA residues were detected in the head and thorax. These results indicate that S. calcitrans may harbor EqHV in their head and thorax regions.

Background From a veterinary-medical point of view, the stable fly, Stomoxys calcitrans , is perhaps the economically most important blood-sucking muscoid fly species (Diptera: Muscidae), owing to its worldwide occurrence, frequently high local abundance, direct harm caused to livestock, pet animals and humans, as well as its vector role. Considering the latter in the context of protozoan parasites, the stable fly is a mechanical vector of trypanosomes and Besnoitia besnoiti . However, its role as a vector of piroplasms appears to be seldom studied, despite old data suggesting mechanical transmission of babesiae by dipteran flies. Methods In this study 395 stable flies (and one Haematobia stimulans ) were collected at a cattle farm with known history of bovine theileriosis, and at further nine, randomly chosen locations in Hungary. These flies were separated according to sex (30 of them also cut into two parts: the head with mouthparts and the thorax-abdomen), followed by individual DNA extraction, then screening for piroplasms by PCR and sequencing. Results In stable flies, Theileria orientalis  and T. capreoli were identified at the cattle farm and T. equi was identified in three other locations. At the cattle farm, significantly more male stable flies carried piroplasm DNA than females. There was no significant difference between the ratio of PCR-positive flies between the stable (void of cattle for at least two hours) and the pen on the pasture with cattle at the time of sampling. Among dissected flies (29 S. calcitrans and 1 H. stimulans ), exclusively the thoracic-abdominal parts were PCR-positive, whereas the head and mouthparts remained negative. Conclusions Theileria DNA is detectable in stable flies, in the case of T. orientalis at least for two hours after blood-feeding, and in the case of T. capreoli also in the absence of infected hosts (i.e. roe deer). Male flies rather than females, and thoracic-abdominal (most likely crop) contents rather than mouthparts may pose a risk of mechanical transmission. These data suggest that it is worth to study further the vector role of stable flies in the epidemiology of theilerioses, in which not the immediate, but rather the delayed type transmission seems possible.

Studies related to ants found in hospital environments have aroused interest in their role as mechanical vectors of pathogenic microorganisms. The objective of the current research was to determine the species composition and bacterial contamination of ant species found in a public hospital in the eastern Amazonian region. Ants were captured using bait containing honey and sterilized sardines in 15 locations within the Macapá Emergency Hospital, Amapá. Ants were identified morphologically using specific keys. Bacteria were first inoculed in a Brain Heart Infusion broth and then plated on 5% Agar with blood or MacConkey media. Bacterial species were identified through biochemical procedures. In total, 9,687 ants were collected, with 69.8% from the dry season and 30.2% from the rainy season. Nine species of ants were identified belonging to three subfamilies: the Monomorium pharaonis (Linnaeus 1758) being the most common, comprising 39.2% of the total specimens. Only one ant species was found in each bait, facilitating microbiological analyses. In total, 92 bacteria isolates were identified comprising 12 species. Pseudomonas aeruginosa Schroeter 1872 (Pseudomonadales: Pseudomonadaceae) was pathogenic bacteria, most frequently isolated, comprising 10.9% of the positive samples. The most contaminated ant in the study was M. pharaonis with 38.3%. It was the dominant ant species in this hospital environment. Its wide prevalence, forage day and night of this vector in hospital facilitated bacterial contamination. The presence of bacteria on ants may be associated with the dissemination of pathogens which cause hospital infections, making pest control a necessity in these institutions.

American cockroach ( Periplaneta americana ) has been implicated as mechanical vector of parasites of humans and animals. Therefore, this study aimed to identify and determine the prevalence of human intestinal parasites associated with the body surface and gut of P. americana . A total of 221 cockroaches which include 104 males and 117 females were collected from household kitchen, toilet area and canteen after which they were brought to laboratory for study. The body surface of the cockroach was washed with 5 ml normal saline solution to remove external parasites on the body surface for examination and later rinsed with 70% alcohol and dried before dissecting. The cockroach was dissected to examine internal parasites. Eleven parasites were recovered and identified, these include Ascaris   lumbricoides (51.58%),  Strongyloides stercoralis (48.42%) Trichuris   trichiura (52.49%),  Enterobius   vermicularis ( 37 .10%), Taenia spp (14.93%),  Toxocara  (31.67%), Ancylostoma spp (34.84%), Necator americanus (53.39%), and  Diphylidium spp  (66.23%) Balantidium coli (66.52%). The parasites were recorded both on the body surface and gut of the cockroach. There is no significant difference ( p  > 0.05) between parasites infection rate comparing both sexes; though, female cockroach having a higher infection rate (91.45%) than male (81.5%). Cockroach collected from toilets carried more parasites (96.34%) as compared to those from restaurants/canteen (89.71%) and household kitchens (81.69%). All parasites encountered were pathogenic to human and animals. This study has revealed that P. americana can act as mechanical vector by transporting and transmitting these parasites easily to man and animal. Good sanitary practices, reinforcement of worms' eradication programs, and the fight against these insects remain a necessity to contain the menace of parasites burden and cockroach control.