The two most frequent helminths in our sample were E. vermicularis and Anisakis simplex (75% of all samples). These results coincide with other published studies in which both parasites were found to be the most frequent causes of appendicitis and intestinal obstruction in emergency surgery due to helminth (Dincel et al., 2017; Tayfur & Balci, 2019; Uysal & Dokur, 2017). In addition, a comparative analysis of the two main groups has been carried out. This sub-analysis clearly shows that these two helminths produce very different clinical pictures and therefore require a different therapeutic approach. This clinical difference is remarkable as statistically significant differences were identified concerning age (p < 0.001), diagnostic test (p = 0.032), clinical diagnosis (p = 0.005), and surgical treatment (p < 0.001) (Table 3).
E. vermicularis is the most common parasite in developed countries and the most frequent cause of acute appendicitis (Dincel et al., 2017; Gorter et al., 2017; Taghipour et al., 2020; Yıldız et al., 2015). Several parasites can cause appendicitis, although other parasites, such as Schistosoma are infrequently/rarely detected in non-endemic areas, as in our case (Akbulut et al., 2011). The only case of appendicitis caused by Schistosoma in our series was in a sub-Saharan migrant from Cameroon, where this parasite is endemic. Similarly, A. lumbricoides worms are localised in the proximal jejunum and ileum and rarely cause appendicitis. The only case of A. lumbricoides appendicitis occurred in a Spanish patient who reported no risk factors or recent travel abroad. The parasite causes appendicitis by mechanical obstruction of the lumen. Interestingly, a protective role of appendicitis has been attributed to the intestinal infection of E. vermicularis through the control inflammation caused by bacteria (Taghipour et al., 2020) particularly in Caucasian girls (Lala & Upadhyay, 2016). However, this hypothesis remains controversial (Yildirim et al., 2005).
he other most frequent parasite in our series was Anisakis simplex, which is linked to raw or undercooked marine fish or squid consumption. A. simplex, Anisakis pegreffii, and Phocanema decipiens belong to a group of nematodes that accidentally infect humans during their reproductive cycle (EFSA Panel on Biological Hazards (BIOHAZ), n.d.). Once ingested, A. simplex can rupture the gastrointestinal mucosal lining, enter the intestinal mucosa, and form a granuloma, where it dies a few weeks later (Bucci et al., 2013; Kliks, 1986).. Its clinical presentation is severe epigastric pain due to the larval invasion of the mucosa, and serological IgE determination is helpful in the diagnosis. Treatment is based on larva removal after visualization with endoscopy when it is located on the stomach, but intestinal or ectopic cases require surgical removal. Spain is a large consumer of fish, although, in traditional cuisine, the fish is usually adequately cooked (Hosoe et al., 2014). Probably due to governments' sanitary and hygienic sanctioning measures, the incidence of Anisakis is on the decline. This argument is in line with the trend in our sample. As shown in Fig. 1, the prevalence of parasitosis in our sample shows a clear downward trend. At the beginning of the period, the incidence was three patients per year and decreased to less than 1 case per year.
Parasitosis by other helminths was rare. In fact, in some cases, only one is in the whole series. It should be noted that only emergency surgeries for Echinococcus were included in this series. Obviously, abdominal surgeries for this cause were more frequent in this period, but the aim of this study was different, so only cystectomies and emergency drainage for this cause (n = 3) were reported; moreover, one of the two exits in the sample corresponds to a patient who presented multi-organ failure with a fatal outcome.
It is essential to mention that, sometimes, the parasite could be an incidental histological finding without causative implication (Pehlivanoğlu et al., 2019). Nonetheless, in all of the patients, the inflammation of the appendices required surgery, independently of the parasite's implication. On the other hand, advances in radiodiagnosis have made it possible to differentiate true appendicitis from other inflammatory conditions that do not require emergency surgery. The surgery was adequate in all the cases reported, regardless of the parasite diagnosis. The patients required the surgical approach (Gorter et al., 2017), despite some authors suggesting that surgery might not be necessary (Dunphy et al., 2017).
Along with surgical treatment, patients are usually treated with an anthelmintic drug. For example, E. vermicularis cohabitants and close contacts should be treated if more partners are affected, or the infection is recurrent (Sosin et al., 2019).
However, most of the reviews about smaller retrospective case series or clinical cases, and although infrequent, surgeons will continue to be confronted with these diagnostically and therapeutically challenging disease patterns.