In Vitro Ovicidal Activity of Nematophagous Fungus Paecilomyces lilacinus on the Eggs of Parasitic Helminths

Parasitic helminths eggs released into the environment through defecation of definitive hosts are affected by various environmental factors [1]. It is believed that these eggs are also invaded and eliminated by different biological agents including fungi [2]. Nematophagous fungi are potential agents for biocontrol of helminths eggs; these fungi, divided into predators, endoparasites, and ovicidals, can survive in soil as saprophytes and colonize the helminths eggs [3]. More than 150 species are known to interfere with the development of helminths eggs in soil [4], among these Paecilomyces lilacinus (Thom) Samson from the class hyphomycetes has received more attention. Previously, this species demonestrated a high in vitro ovicidal activity on Toxocara canis eggs and was recommended as a potential agent for biological control of the zoonotic helminths in outdoors [5]. Defecation of animals is not only the primary transmission route of helminths eggs in outdoors, but also in animal houses leading to infection of experimental animals and the laboratory staff as well [6]. Adopting non-chemical approaches, e.g., using fungi as biological agents for decreasing the helminths eggs in animal husbandries may intervene with transmission cycle of these parasites. These agents may as well prevent the unfavorable effects of chemical agents on the experimental animals, which may adversely affect the results of tests. The species, Syphacia obvelata, Hymenolepis diminuta [7], and Echinococcus granulosus are the known causative agents of zoonotic helminth infections in Iran [8]. Syphacia obvelata commonly infects laboratory animals, e.g., mice and rats [9]; the short and the direct life cycle of S. obvelata can result in a high prevalence of this helminth infection among laboratory mice [10]. Hymenolepis diminuta is more common in wild rodents and rarely affects laboratory animals [9], which may infect technicians and researchers as well [11]. Echinococcus granulosus the causative agent of echinococcosis not only causes health problem, but also results in economic losses and animal productivity losses [12]. In the present study, we searched for nematophagous fungi in the soils collected from different areas of Iran and evaluated the ovicidal activity of the fungus P. lilacinus on the eggs of three above mentioned zoonotic helminths. Introduction: The nematophagous fungi have been suggested as an alternative way to eliminate the zoonotic helminths eggs from the environment. In the present study, we evaluated the ovicidal activity of a fungus, Paecilomyces lilacinus, recovered from a compost soil, on the eggs of parasitic helminths under in vitro condition. Methods: Water suspension of the soil samples collected from different areas of Iran were transferred to 2% water-agar culture media baited with Rhabditis sp. larvae. The nematode larvae trapped by fungi were transferred to potato dextrose agar (PDA) media. The sequencing of a beta-tubulin gene identified the nematophagous fungi as P. lilacinus. Eggs of three helminth species, Syphacia obvelata, Hymenolepis diminuta and Echinococcus granulosus were exposed to one isolate of the recovered fungi, and the ovicidal activity was monitored for up to 21 days. Results: Out of 300 samples, only three compost soils, contained the nematophagous fungus P. lilacinus. Microscopical examinations revealed invasion of the helminths eggs by the P. lilacinus. The eggs of H. diminuta were more vulnerable to this fungus invasion while E. granulosus eggs were the least affected ones (P<0.05). Conclusion: Paecilomyces lilacinus can grow on fresh feces and attack the eggs of the parasitic helminths. Therefore, a combination of its hyphae with feces or administration of the spores in the animals’ food may reduce the helminths eggs in the environment and consequently intervene with the transmission of parasitic helminthes in the animal houses. J Med Microbiol Infec Dis, 2016, 4 (3-4): 52-56.