Case Report: Hymenolepis diminuta in an asymptomatic Ecuadorian child.

Introduction

The cestode Hymenolepis diminuta (Rudolphi 1819, Weinland 1858) is a cosmopolitan parasite, which in the adult stage is usually found in the small intestine of rats and accidentally in humans. Its biological cycle develops with the intervention of an arthropod, which becomes infected by ingesting the eggs of H. diminuta, which are found in the feces of parasitized rats.¹

The mechanism of infection begins when coprophilic arthropods ingest the eggs of H. diminuta which are eliminated in rodent feces and act as obligate intermediate hosts of the cestode. When humans accidentally ingest these infected arthropods, the cysticercoids in the insect’s hemocele develop into adults in the human’s small intestine, where eggs are then produced and expelled in defecation. Human infection through direct ingestion of H. diminuta eggs has not been reported.²

Several coprophilous arthropods such as fleas, weevils, lepidoptera and beetles have been described as intermediate hosts,³ as well as different species of beetles of the genera Tribolium and Tenebrio.⁴ Experimentally, it has been shown that 90 species of arthropods can serve as intermediate hosts.⁵ Although, Joyeux⁶ pointed to Tenebrio molitor, Ceratophyllus fasciatus and Xenopsylla cheopis as the usual sources of rat infestation, the beetles of the genus Tribolium are those indicated by the scientific literature, as the most frequent in rats and human infections.

The adult cestode of H. diminuta is 20 to 60 cm long, its scolex is rounded and small with four cup-shaped suckers, it has a rostellum without hooks, which is invaginated in a cavity located in the most apical portion of the scolex. The strobilar chain contains three characteristic portions of proglottids: immature, mature, and gravid; The latter, when detached from the strobilus, disintegrates and releases the eggs that are eliminated along with the feces.⁷ The eggs are round, yellow, 60 to 80 microns, with a thick outer membrane and a small oncosphere inside, with three pairs of hooks and no polar filaments.⁸

Clinically, as in Hymenolepis nana infection, parasitosis can be asymptomatic. In infections with a high parasite load, the most frequent symptoms of H. diminuta hymenolepiasis are digestive, with abdominal pain and diarrhea prevailing; irritability and anal itching may also occur^2,3,9 and in some cases patients with skin conditions have presented.^10,11

It is an uncommon infection in humans; however, the prevalence is high in some places: 7.8% in schoolchildren between 6 and 15 years of age in Magdalena in Cajamarca¹² and 7.1% in the population of Tingo María in Huánuco in Peru.¹³ It can be deduced that food, stored in contact with rats and beetles, when consumed constitutes the means of infection, through ingestion of infected beetles. Few cases are reported in adults in the literature³ and most cases have been described in children,^{2,9–11,14–17} probably due to ingesting the infected arthropods, without paying attention. However, a 2020 review of H. diminuta¹⁸ states that, out of 130 infections in humans, the age of the infected individuals was: 2.3% infants (≤1 year old), 66.2% children (2 to 9 years), 20% adolescents (10 to 19 years old), and 11.5% were adults (≥ 20 years old).

Regarding geographical location, the review by Panti-May et al.¹⁸ reports that human infections with H. diminuta were reported in 80 countries around the world from 1810 to 2018. Most cases were reported in the Americas (n = 815), Southeast Asia (n = 226) and Eastern Mediterranean (n = 210). Three countries exhibited more than 100 records: Costa Rica (n = 320), the United States of America (n = 181), and Brazil (n = 140).

In Ecuador, the presence of Hymenolepis spp. has been described¹⁹ in stray dogs on the coastal beaches of Ecuador, Hymenolepis nana and diminuta have also been reported in rodents (Rattus norvegicus and Rattus rattus) from the city of Milagro.²⁰ Only one case has previously been reported of this species in a two-year-old Ecuadorian girl, however, the finding was made in Spain¹¹; This case describes that in 2003 it arrived in that continent and in the first half of 2004 it presented gastrointestinal symptoms, detecting the parasite in feces. In 2007, research by Jacobsen et al.²¹ indicated a 1% prevalence of H. diminuta when evaluating 203 samples from children between 12 and 60 months of age; however, no reference was made to clinical or sociodemographic data of the infected children. Since then, no other case of infection in humans has been described in the country, so the case of an asymptomatic child from Portoviejo, Ecuador, is presented.

Case report

In February 2024, the stool sample of a 3-year-old child was received at the Parasitology laboratory of the Technical University of Manabí. On macroscopic examination, the sample showed a soft, greenish-brown consistency, without mucus, pus, or blood; There are also no obvious food residues. Microscopic examination with physiological saline, showed eggs morphologically compatible with eggs of Hymenolepis diminuta ( Figure 1A,B). These had their characteristic brown color, large size and absence of polar filaments. They were measured with a micrometer scale, where 4 of them measured 60 microns and 1 measured 70 microns in diameter. In addition to the coproparasitological examination, the Ritchie-Frick concentrate²² was performed, where no other intestinal parasites were observed, only the eggs of H. diminuta.

Figure 1. (A) H. diminuta eggs at 100 × magnification, physiological saline; (B) Eggs of H. diminuta at 400 × magnification, physiological saline.

When the father is consulted, he indicates that the child did not have gastrointestinal symptoms and that the stool test was carried out as part of the annual health evaluation that he performs. When reviewing the rest of the tests performed, it was observed in the hematology: Leukocyte count within the reference values: 7.15×102/μl (5.0 to 10.00), but with a decrease in neutrophils: 1.59×102/μl (2.10 to 8.90), an increase in lymphocytes: 4.64×102/μl (1.30 to 4.60) and a slight increase in eosinophils: 5.2% (0.0 to 4.0). Hemoglobin 12.5 g/dl (10.5 to 13.5 g/dl), Hematocrit: 36.0% (32.0 to 40.0%). The results show that, although C-reactive protein was within the reference values: 0.33 mg/L (0.00 to 5.00 mg/L), there was a significant increase in the value of Immunoglobulin E (IgE): 1.376 IU/ml (0.0 to 60.0 IU/ml).

To assess the child’s living conditions, his home was visited. The house is in a peri-urban community of the city of Portoviejo (Colón parish). Although Colón is considered an urban parish, the house is in a wooded area of the parish, and in the back has an abundance of intricate trees. In general terms, the house is neat and has the basic services of water, electricity, and septic tank, for the disposal of excreta. There is a chance of rats and mice in the back wooded area, which is ideal for synanthropic animals. During the visit, the presence of beetles (genus Hexodon) is observed and since there are dogs, the presence of fleas, which have been described as intermediate hosts of H. diminuta, cannot be ruled out.

The child received anthelmintic treatment with Albendazole suspension 400 mg/20 mL, 2 bottles, one per day. On the 4th day after treatment, a post-treatment stool examination was performed and eggs were still observed, which were quite altered in their morphology and difficult to identify. Subsequently, 10 days after the end of treatment, the stool examination showed no evolutionary forms of parasites.

Discussion

Hymenolepis diminuta infection is a cosmopolitan zoonosis that is mainly rural and infrequent in humans. As of 2020, 1,561 published records of H. diminuta infection had been identified in 80 countries¹⁸; mainly reported in children.^{2,9–11,14–17}

Although, the child in this case, did not present clinical manifestations and most of his laboratory tests were within the reference ranges, the high IgE value found is remarkable. The child did not suffer from allergies, so this situation was ruled out as the cause of the increase. Helminth infections have been mainly related to blood eosinophilia^23–25 and a similar situation has only been reported in terms of increased IgE in a child with H. diminuta in Italy¹⁰ who presented atypical allergic manifestations.¹¹ In this research, it is pointed out that the infected 2-year-old child presented remitting fever (maximum peak 37.7 °C), abdominal pain, diffuse skin itching, transient chest rash and arthromyalgia and in the same context, the case of the Ecuadorian girl in Spain is presented, who manifested atopic dermatitis, self-limited diarrhea, vomiting and constipation, unlike the current case, there were no allergic manifestations or any symptoms, only the elevation of IgE. Unfortunately, in this case, no information was obtained on the post-treatment IgE values, to evaluate their direct relationship with parasitosis.

Allergic symptoms are often present in chronic helminth infections, caused by a constant state of immune activation characterized by a dominant type of Th2 cytokine profiles and high IgE levels.^26,27 However, eosinophilia is not usually seen in helminth infections that reside in the lumen of the human intestine, as is the case with H. diminuta. However, helminth infections can affect the expression of an allergic disease and, in certain situations, may be associated with a higher, lower, or no risk of atopic conditions.^28,29

Another important point to highlight is the anthelmintic treatment applied, since the literature reports that the first choice anthelmintics are praziquantel and niclosamide,³ therefore, it has been the treatment of choice in several studies.^{9–11,14–17} However, in this case, albendazole was indicated, a treatment also applied in a case reported by Rivero et al.² in Venezuela, demonstrating effectiveness in the treatment of parasitosis, as no eggs were observed in successive samples. It is known that first-choice drugs are given in single doses, however, Tena et al.¹⁴ indicated in their study to repeat the dose three times, even increased, until the parasite was eliminated, so albendazole can be considered as an alternative treatment.

Conclusions

It is feasible to find H. diminuta infection in Ecuadorian children, although in an infrequent way, so the microscopist should be alert to the finding of eggs like those of Hymenolepis nana, but larger and dark brown in fresh preparations. Likewise, medical personnel should not rule out the possibility of this parasitic species in children, mainly under five years of age; even in children without clinical manifestations. The report of this case, aims to alert health personnel about the possibility of finding this cestode in Ecuadorian children, and contribute to the epidemiology of intestinal parasitosis in the country.