Belonging to the class Pentastomida, Linguatula serrata and its haplotypes and potentially closely related Linguatula species are zoonotic arthropods (Hendrix, 1998) which usually infect dogs, and occasionally, foxes, cats and other carnivores as the final host and herbivores as the intermediate host. The adult parasite can be detected in the upper respiratory system, nasal airways and frontal sinuses of the final host (Hendrix, 1998). Nasopharyngeal discharges of the final host spread the egg into the environment which are then consumed by the intermediate herbivore host. Following emergence from the eggs, the larva spread throughout the internal organs of the intermediate host reaching the mesenteric lymph nodes (MLNs), liver, lungs and spleen, where they develop into infective nymphs. The final hosts are infected following ingestion of the infested viscera of intermediate hosts (Tavassoli et al., 2018).

Human infection with L. serrata occurs following consumption of raw or undercooked infected liver, lungs or other infected organs of the intermediate host and can manifest as a nasopharyngeal or Halzoun disease. Within Iran, the consumption of a delicious food called Joghul and Boghul, in which the liver, lungs and intestines of primarily sheep but also other ruminants are briefly cooked, can lead to Linguatula infection if these organs are infected with the nymphal stage. In humans, the nymph and/or mature parasites migrate to the nasopharyngeal tract and frontal sinuses leading to a variety of symptoms, ranging from mild inflammation of the upper respiratory tract to temporary conductive deafness (Khalil et al., 2013). The visceral form of the infection occurs when humans consume water or vegetables contaminated with eggs and, depending on the organ system involved, a range of symptoms including abdominal pain, chronic cough, or night sweats can be observed (Mateva et al., 2013). Most research on the epidemiology of Linguatula spp. and sources of human infection have focused on mesenteric and/or mediastinal lymph nodes of ruminants (Hajipour and Tavassoli, 2019; Nourollahi et al., 2011, Nourollahi et al., 2010; Oryan et al., 2011; Sudan et al., 2014; Tajik et al., 2008; Tavassoli et al., 2007a, Tavassoli et al., 2007b). Fewer studies have been performed on liver or lung infection of various animals with Linguatula spp. nymphs (Haddadzadeh et al., 2010; Hami et al., 2009; Morales Muñoz et al., 2020; Oryan et al., 2011; Shakerian et al., 2008; Shekarforoush et al., 2004; Tajik and Sabet Jalali, 2010; Yakhchali et al., 2009). Although Linguatula is a public health issue, there is no standard and comprehensive method for diagnosing the infection in offal during abattoir inspection. Ruminant infection has no considerable clinical signs and such animals are major sources of infection for humans. Hence, it is necessary to understand the prevalence and risk factors for the parasite in ruminants and to identify efficient disinfection and inactivation methods to improve food safety and public health.

The purpose of this research, therefore, was to assess the prevalence of Linguatula spp. nymphal stages in liver and lungs of ruminants slaughtered at the Tabriz abattoir in the northwest of Iran and identify possible factors, such as season, age, and sex, associated with the infestation. In addition, the effects of temperature and salinity on survival of Linguatula spp. nymphs in infected livers and lungs of ruminants were investigated.