Evaluating the role of synanthropic filth flies in the transmission of zoonotic parasites: field and laboratory evidence from different animal rearing sites in upper Egypt with focus on Cryptosporidium spp

Abstract

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.

Keywords: Cryptosporidium; Animal farms; Filth flies; Mechanical vector; Nested PCR; Sequencing; Upper Egypt; Zoonotic parasite infections.

Fig. 1

A satellite image from Google Earth showing the studied animal sites (A, B, and C)

Fig. 2

Micrographs show protozoan parasites isolated from fly pools stained with different stains. Cryptosporidium spp. oocysts, a = Direct smear, b = Iodine stained, and c, d = Ziehl–Nielsen stained, 100 × oil immersion. Giardia spp. cyst, e = Direct smear, f = Iodine stained, and g = Methylene blue stained 40x. Entamoeba spp. cyst, h = Direct smear, i = Iodine stained 40x. Balantidium coli trophozoites, j = iodine-stained, k = methylene blue-stained 40x. l = Trichomonas spp. trophozoites stained with methylene blue, 40x

Fig. 3

The micrographs show the helminth eggs and larvae isolated from the fly pools. a-h Trichostrongylids whole 1st stage larva (a), larval anterior end showing numerous intestinal cells (b), posterior end of first stage larvae showing short, pointed sheath (c), and Trichostrongylids egg (d). A scanning electron micrograph of Trichlostrongylids larvae showing lateral alae (LA) at the anterior end while the esophagus is not well demarcated (e), posterior end (pe) showing a pointed tail and short sheath (sh) (f). g: Trichuris spp. immature egg, (h): Toxocara vitulorum egg. Lens 40 × and 10x

Fig. 4

External arthropods detected on fly exoskeletons showing different stages of mites (eggs, nymphs, and adults) (a-d). e & f: Midge larvae were detected via direct smearing, iodine-stained and coinfested with other nematode larvae. g & h: Pseudoscorpions infesting Musca domestica and Physiphora alceae fly exoskeletons, respectively

Fig. 5

Nested PCR amplification of the Cryptosporidium COWP gene (A) and the SSUrRNA gene (B) resolved on a 1.5% agarose gel stained with ethidium bromide. Positive PCR products at 553 bp are shown. for the COWP gene and positive amplification products of the SSUrRNA gene in lanes 3 and 6, with single bands at 826 bp. Lane (1A): positive control, lanes (4A and 1B): negative control. (M): DNA marker (Thermo Fisher Scientific, Cat. no. SM0243)

Fig. 6

Phylogenetic tree of parvum cysts inferred via neighbor‒joining analysis of the COWP gene sequence. Cryptosporidium muris (house rat) and Cryptosporidium andersoni (cattle) from China were used as the out-group. Nonparametric bootstrap values (based on 1000 replicates) are shown at each node. The scale bar indicates the number of substitutions per site

Fig. 7

DNA amplification of the COX1 gene in chironomid larvae isolated from fly washes. The PCR products were resolved via 1.5% agarose gel electrophoresis and stained with ethidium bromide. The gel image shows positive PCR products in lanes (1, 4), with single bands at 657 bp. Lane (1): positive control, lane (2): negative control. (M): DNA marker (Thermo Fisher Scientific, Cat. no. SM0243)

Fig. 8

Phylogenetic tree of chironomid larvae inferred via neighbor-joining analysis of the COX1 gene sequence of the Chironomidae family. The red dots represent the sequences obtained in this study. Acricotopus and Ablabesmyia rhamphe were used as the out-group. Nonparametric bootstrap values (based on 1000 replicates) are shown at nodes. The scale bar indicates the number of substitutions per site