Intestinal parasites in rodents from five different Himas in Lebanon

The five Lebanese Hima sites - Kherbet Qanafar, Ras el Matn, Ain Zebdeh, Ebel el Saqi, and Hammana (Fig. 1) - represent Lebanon’s significant ecological and cultural heritage areas. These sites are part of a traditional resource management system known as “Hima,” which emphasizes sustainable use of natural resources while preserving biodiversity. Each site showcases unique landscapes and ecosystems, contributing to the environmental richness of Lebanon.

Fig. 1.

The five Lebanese Hima sites - Kherbet Qanafar, Ras El Matn, Ain Zebdeh, Ebel El Saqi, and Hammana

Sampling was conducted in two seasons, Spring (May and June 2022) and Autumn (September 2022). Twenty-seven trapping stations were deployed for five consecutive nights and covered the different landscapes/habitats present in the Himas. The stations were distributed as follows among the five Himas: 6 stations in Ras El Maten, 6 stations in Hammana, 4 stations in Kherbet Qanafar, 6 stations in Ain Zebdeh, and 5 in Ebel El Saqi. In each station, 10 Sherman® live rodent traps spaced 2 – 4m apart were set at dawn and were checked the next day at dusk in locations close to identified burrows or suitable habitats. The traps were baited with peanut butter, cucumber, sunflower seeds, and canary feed mix. Captured rodents were transferred to the Parasitology Laboratory of the Life and Earth Science Department, Lebanese University - Faculty of Sciences in Fanar. Each rodent was identified to the species level, and its morphological traits, age, and sex were recorded.

Endoparasites were identified based on their morphological traits at the Animal Research and Diagnostics Lab, Faculty of Agricultural and Food Sciences at the American University of Beirut (Tanideh et al., 2010; Koyama, 2013; Kim et al., 2015; Fitte et al, 2018; Maurelli et al., 2021).

Statistical analysis was estimated using the Statistical Package for the Social Sciences (SPSS) version 16.0 computer software program. A binary logistic regression model was used to test the possible relationship between sampling rodent species, gender, seasons, and site. Goodness-of-fit for each model was assessed using the Receiver Operating Characteristic (ROC).

Hymenolepis diminuta was the second most prominent parasite (11.7 %) among the trapped rodents (Fig. 6A). It was found in 14.3 % of the captured Apodemus mystacinus (Table 1). The total number of infected individuals with H. diminuta in the Spring (7.8 %) was more than those captured in the Fall (3.9 %) (Table 2). The comprehensive model assessing the factors influencing the infection of rodents with Hymenolepis diminuta accounted for 88.3 % of the variance, demonstrating a strong fit with a Receiver Operating Characteristic (ROC) value of 0.799. The location where the rodents were captured emerged as the most significant factor in determining the presence of Hymenolepis diminuta (Table 3).

Ascaris lumbricoides was the most prominent parasite among the trapped rodents (31.7 %) (Fig. 6B). It was found in 33.3 % and 47.4 % of the captured Apodemus mystacinus and A. flavicollis, respectively (Table 1). The total number of infected individuals with A. lumbricoides in the Spring (17.1 %) was higher than those captured in the Fall season (14.6 %) (Table 2).

The comprehensive model assessing the factors influencing the infection of rodents with Ascaris lumbricoides accounted for 68.3 % of the variance, demonstrating a robust fit with an ROC value of 0.742. This indicates that the model effectively distinguishes infected and non-infected rodents. Among the various factors analyzed, the rodents’ capture location and the seasonal conditions were the most significant determinants of Ascaris lumbricoides presence (Table 3). Hence, rodents caught in the Spring were less likely to be infected by Ascaris lumbricoides, while rodents caught in Ain Zebdeh were most likely infected with Ascaris lumbricoides.

Trichuris muris was found in 7.8 % of the trapped rodents (Fig. 7C, D). It was observed in two captured species: Apodemus mystacinus (7.7 %) and A. flavicollis (21.0 %) (Table 1). The total number of infected individuals with T. muris in the spring (6.8 %) was higher than that of those captured in the fall (1 %) (Table 2). The comprehensive model assessing the factors influencing the infection of rodents with Trichuris muris accounted for 91.7 % of the variance, demonstrating a robust fit with an ROC value of 0.619. The season tended to play the most important role in determining the presence of Trichuris muris (Table 3), whereby rodents caught in the Spring season tended to be more infected by this parasite.

Fig. 7.

Intestinal helminths under stereoscope: (A) Hymenolepis diminuta, (B) Male Ascaris lumbricoides, (C) Female Trichuris muris, (D) Male Trichuris muris, (E) Male Heligmosomoides polygyrus, (F) Female Heligmosomoides polygyrus, (G) Capillaria spp, (H) Physaloptera spp., (I) Physaloptera spp. head.

The parasite Aspiculuris tetraptera was found in 7.3 % of trapped rodents (Fig. 8A). It was observed in four captured species of rodents: Apodemus mystacinus (5.9 %), A. flavicollis (15.8 %), A. hermonensis (12.5 %), and Microtus guentheri (14.3 %) (Table 1). The total number of infected individuals with Aspiculuris tetraptera in the Spring (4.4 %) was higher than those captured in the Fall season (2.9 %) (Table 2). Species of rodents, gender, season, and study site had no significant impact on the prevalence of A. tetraptera among the species caught (p>0.05).

Fig. 8.

Intestinal helminths under the microscope (magnification 40 x): (A) Aspiculuris tetraptera, (B) Female Syphacia muris, (C) Male Syphacia muris, (D) Female Syphacia obvelata, (E) Male Syphacia obvelata.

Heligmosomoides polygyrus was found in 6.8 % of trapped rodents (Fig. 7E, F). Around 7 % of the trapped Apodemus mystacinus and 10.5 % of A. flavicollis were infected with this specific worm (Table 1). The total number of infected individuals was equal in both seasons (3.4 %) (Table 2). Species of rodents, gender, season, and study site had no significant impact on the prevalence of H. polygyrus among the species caught (p>0.05).

Syphacia muris was found in 4.2 % of the captured Apodemus mystacinus (3.9 % of the total trapped rodents (Fig. 8B, C, Table 1). The other captured rodent species did not harbor this worm. Rodents caught in the Spring season (1.5 %) were slightly less infected with S. muris than those captured in the Fall season (2.4 %) (Table 2). The overall model assessing the factors influencing the infection of rodents with Syphacia muris accounted for 96.6 % of the variance, and the model’s fit was deemed satisfactory with an ROC value of 0.696. The season tended to play the most important role in determining the presence of Syphacia muris (Table 3). Hence, rodents caught in the Fall season were more likely to be infected by Syphacia muris.

This nematode was found in 3.4 % of trapped rodents (Fig. 8D, E). Only A. mystacinus individuals were infected with this helminth at a rate of 3.6 % (Table 1). The total number of infected individuals with S. obvelata in Spring (2.4 %) was slightly higher than those captured in Fall (1 %) (Table 2). Species of rodents, gender, season, and study areas had no significant impact on the prevalence of S. obvelata areas among the species caught (p>0.05).

Capillaria spp. was found in 2.4 % of the trapped rodents (Fig. 7G). It was observed in two rodent species, namely Apodemus mystacinus and Apodemus flavicollis (Table 1). The total number of infected individuals with Capillaria in the Spring season (1.5 %) was slightly more than those captured in the Fall season (1 %) (Table 2). Species of rodents, gender, season, and study site had no significant impact (p>0.05) on the prevalence of Capillaria spp. among the captured species.

Physaloptera spp. was found only in one rodent (A. mystacinus) in the Spring season in Ain Zebdeh (Tables 1, 2, Fig. 7H, I).

Hymenolepis diminuta is a prevalent worldwide parasite with zoonotic potential, identified as the second most prominent parasite (11.7 %) among trapped rodents in this study. Although our work reported the presence of H. diminuta only in Apodemus mystacinus, various researchers have documented its presence in different rodent species in the Middle East, including Apodemus fla-vicollis, A. sylvaticus, A. Agrarius, Mus musculus, Rattus rattus, and Rattus norvegicus (Malla & Saida, 2022; Majede & Al-Amery, 2021a; Younis et al., 2021; Majede & Al-Amery, 2021b; Mohtasebi et al., 2020; Nabeel & Al-Tameemi, 2019; Abu-Madi et al., 2005; Gubanyi et al., 1992). Our findings of no gender-biased parasitism support previous studies (Malla & Saida, 2022; Archer et al., 2017) but contrast with others that found male-biased parasitism in urban settings of Lahore, Pakistan (Majeed & Al-Amery, 2021a; Ahmad et al., 2014), suggesting that ecological factors may influence these dynamics differently across regions. This variation was attributed to males moving from one community to another more frequently than females, thus having a greater chance of getting an infection from infected intermediate hosts.

The number of rodents infected with the cestode H. diminuta was not influenced by seasonal changes, indicating that its life cycle remains unaffected by climatic conditions at our study locations. In agreement with this finding, Ahmad et al. (2014) noted that infection rates of this cestode do not vary with seasonal fluctuations but are instead determined by the level of interaction between the intermediate host and the definitive host in rodent populations. The overall characteristics of the study sites did influence the presence of H. diminuta; this nematode was found in rodents across all trapping locations except for Ebel El Saqi, exhibiting varying prevalence (P<0.001) among these sites. The observed abundance of H. diminuta may indicate that the environmental conditions at our study sites are conducive to its survival and transmission, particularly due to the availability of its intermediate host, grain beetles, in these areas.

The life cycle of the nematode species Ascaris lumbricoides is usually direct (Ransom & Foster, 1919) with zoonotic potential (Peng et al., 2007). Ascaris lumbricoides was the most (31.7 %) prominent parasite among the trapped rodents. Our findings also indicate that this helminth is reported for the first time as an infective agent in Apodemus mystacinus and A. flavicollis. Gender-biased parasitism was not observed in rodents infected with A. lumbricoides. This may reflect the equal susceptibility and exposure of both genders of the vector to this nematode (Smith et al., 2001). However, trapped rodents were most infected with A. lumbricoides in the Ain Zebdeh site during the Fall season. The seasonal and habitat differences in the infection rates can be attributed to the sensitivity of nematode transmission to climatic and habitat conditions. For instance, variations in temperature and humidity, as well as vegetation cover, affect the transmission of this parasite. During the fall season, leafy and root vegetables were available in Ain Zebdeh, an agricultural land, providing food resources that aided in the transmission of parasites. On the contrary, Fueki (1952) found that the infection of Ascaris from vegetables occurs more frequently in the spring when leafy vegetables are abundant in the market and the temperature is high enough for developing Ascaris eggs. The findings have highlighted that even the protected areas can facilitate the transmission of helminths due to the close interactions between wildlife and their ecosystems. For instance, rodents in these regions may harbor high prevalence rates of Ascaris lumbricoides due to factors such as abundant food sources and minimal disturbance from human activities. This prevalence is concerning because it suggests that these areas could act as reservoirs for the parasite, potentially leading to spillover infections in humans who come into contact with contaminated soil or water sources within these ecosystems.

The nematode Trichuris muris has a direct life cycle, and it serves as a model of the gastrointestinal nematode Trichuris trichiura that infects humans (Marchiondo et al., 2019). Our findings agree with previous studies reporting the presence of this worm in Apodemus spp. It was reported across Europe in Apodemus sylvaticus, Apodemus flavicollis, Mus domesticus, and Rattus rattus (Callejón et al., 2010). In Kurdistan Province, West of Iran, T. muris was reported in the cecum of six types of rodents, including Apodemus witherbyi, Microtus qazvinensis, Mus macedonicus, Dryomys nitedula, Meriones libycus, and Meriones persicus (Mohammadi et al., 2022). The number of rodents infected with T. muris showed no variation among genders, which is consistent with the results of Kataranovski et al. (2011), who reported the absence of an effect of host gender on the parasitism for T. muris species in Rattus norvegicus in Serbia. Our results oppose those of Hepworth et al. (2010) and Hayes et al. (2007), who found that females are more resistant to infection. In contrast, males become chronically infected in Laboratory mice, which is attributed to the sex hormones, which are important factors in developing immunity in susceptible mice.

Seasonal variations significantly influence the prevalence of T. muris infections, with a notable increase in infected rodent populations during the Spring. This season creates conditions that are more convenient for the spread of T. muris eggs, as the life cycle of Trichuris spp. is adversely affected by harsh climatic factors such as intense sunlight, extreme temperatures, and insufficient moisture. Research indicates that optimal moisture levels and moderate temperatures are crucial for the survival and transmission of Trichuris eggs (Fahmy, 1954).

The nematode Aspiculuris tetraptera has a direct life cycle (Gerwin et al., 2017), and adult worms are typically located in the large intestine of mice (Whary et al., 2015). The prevalence of this parasite among four different rodent species shows no significant variation, suggesting that the infection is not specific to any particular species. This observation aligns with Behnke’s (1974) findings, which documented infections in the colons of various rodent species, including Mus musculus, Rattus norvegicus, and Apodemus sylvaticus. Additionally, there is no notable difference in infection rates between male and female rodents, supporting earlier studies (Kataranovski et al., 2008; Kia et al., 2010) that indicate equal susceptibility to this nematode across genders. However, our findings contrast with those of Li et al. (2023), who reported a male-biased parasitism in A. tetraptera infections among Brandt’s Voles (Lasiopodomys brandtii) in China, attributing this bias to males providing a larger ecological niche for parasitic invasion.

The season did not affect the number of rodents infected with this parasite. This could be explained by the absence of extreme variations between different seasons that affect the life cycle of A. tetraptera and its transmission (Li et al., 2021). In addition, the number of rodents infected with A. tetraptera did not vary among different trapping sites, probably due to the simple life cycle and the short incubation period of the A. tetraptera parasite. Likewise, Li et al. (2023) found no variation between habitat types (steppe and grazing) in infected Brandt’s Voles of China.

Heligmosomoides polygyrus species has a direct cycle of infecting the small intestines of rodents (Marchiondo, 2019). The fact that our study reports the presence of this worm in rodents of the Apodemus spp. is in agreement with previous studies (Behnke, 2008; Eira et al., 2006). Furthermore, gender-biased parasitism was not observed in rodents infected with H. polygyrus, which agreed with the findings of Wertheim and Durette-Desset (1975). However, previous works reported a female-biased sex ratio in transmitting this parasite among rodents that may be caused by differences in immunity or host behavior (Ferrari et al., 2007; Wertheim and Durette-Desset, 1975). The fact that seasonality did not have any impact on the abundance of H. polygyrus in trapped rodents opposed the findings of Eira et al. (2006) that showed that the highest frequencies of Apodemus sylvaticus infection with H. polygyrus were reported during the humid Spring season. Moreover, Behnke’s (2008) observations reported a tendency of infection with H. polygyrus after periods of high humidity, where conditions become suitable for their development and transmission, which was not the case during our study.

The nematode Syphacia muris has a direct life cycle (Lewis & D’Silva, 1986) and does not pose a zoonotic risk to humans (Lewis, 1968). Our research identified S. muris exclusively in the species Apodemus mystacinus. However, previous studies have documented the presence of this parasite in Apodemus wetherbyi in Iran (Mohammadi et al., 2022) and in black rats in Egypt (Menshawy et al., 2021).

Additionally, the prevalence of mice infected with S. muris was influenced by seasonal changes, showing a higher infection rate during the fall season. This finding is consistent with the observations made by Gomez Villafañe et al. (2008), who reported that S. muris was only found in Rattus norvegicus during the fall months in Argentina. The increased infection rates during this time are related to rat behaviors, particularly their grooming habits, which may facilitate the spread of the parasite.

The life cycle of the nematode Syphacia obvelata is direct, primarily affecting the gastrointestinal tract of rodents and recognized as a potential zoonotic helminth (Whary et al., 2015; Riley, 1919). Our study observed that S. obvelata was present only in Apodemus mystacinus. Infection with this nematode has been documented in several rodent species, including brown rats, black house rats, house mice, lesser short-tailed gerbils, and both laboratory rats and mice (Khalil et al., 2014). Furthermore, our findings indicated no gender bias in parasitism among infected rodents. This aligns with the observations made by Yousefi et al. (2014), who also reported an absence of gender-biased parasitism in Mus musculus and Apodemus sylvaticus. The lack of disparity suggests that both male and female rodents have similar levels of exposure to and susceptibility to this nematode. Seasonality did not influence the number of rodents infected with S. obvelata. This shows that the life cycle of S. obvelata was not affected by the climatic conditions in our study sites. On the contrary, it was reported that the infection of male mice with S. obvelata in Gilloud Island was more pronounced during the warm season (the middle–end of the breeding season) (Pisanu et al., 203). The results were explained by endocrine-related increased host susceptibility, which was influenced by host age-related changes in the population rather than by host density-related factors.

In this study, Capillaria spp. was observed only in rodents of the Apodemus spp. namely A. mystacinus and A. flaviciollis. In literature, Capillaria spp. was reported in the intestinal tract of various rodent species such as Bandicota bengalensis, Bandicota indica, and Bandicota savilei in Bangladesh (Fuehrer et al., 2012) and in the intestinal tract of Rattus norvegicus in Serbia (Kataranovski et al., 2011). Additionally, no evidence of gender-biased parasitism was found in rodents infected with Capillaria spp. This observation suggests that both male and female rodents captured in the study exhibit similar levels of susceptibility and exposure to this nematode. However, these findings contrast with those reported by Kataranovski et al. (2011), who identified a higher prevalence of Capillaria spp. infections in male Rattus norvegicus. They attributed this increased infection rate to the overlapping home ranges of males, which may lead to greater exposure to the parasite. At the same time, reproductive females tend to have a more defined site-specific organization that could result in lower transmission rates.

The genus Physaloptera, which belongs to the family Physalopteridae, comprises over 100 known species of parasites found worldwide. These parasites have an indirect life cycle, utilizing beetles, cockroaches, and crickets as intermediate hosts. Consequently, the distribution of these vector species influences the life cycle of Physaloptera spp. (Moradpour et al., 2018).

Our study observed that only one female A. mystacinus in Ain Zebde was infected with this parasite. This limited finding hinders our ability to evaluate how factors such as rodent species, gender, seasonal variations, and trapping locations affect the infection rate. Additionally, these results indicate a low prevalence of rodent infections with this specific parasite in Lebanese Himas.

The absence of protozoan parasites such as Giardia, Toxoplasma, or Eimeria in our study’s rodent samples raises questions about the ecological and biological factors influencing parasite prevalence. Research indicates that different rodent species are susceptible to protozoan infections based on their habitat, diet, and immune responses. For instance, previous works have shown that particular species like Rattus norvegicus often harbor protozoa due to their scavenging behavior and close association with human environments (Chagas et al., 2017). In contrast, rodents inhabiting more isolated or less disturbed habitats may show lower infection rates. A study conducted in Qatar found that while some Apodemus species were hosts to various protozoa, others showed minimal or no infections (Islam et al., 2024). This suggests that environmental factors and host behavior significantly influence the presence of these parasites. A comprehensive study by Singla et al. (2008) noted that many wild rodents exhibit very low prevalence rates for protozoan parasites due to factors such as seasonal variations and habitat conditions. Furthermore, a study focusing on Lebanese wildlife rodents indicated that helminths are more commonly reported than protozoa among small mammals (Abi-Said et al., 2022). This aligns with our findings and suggests a trend where helminths dominate over protozoan infections.

It is worth noting that sample size and diagnostic approaches could influence the detection rates of protozoan parasites. Our study relied primarily on the floating technique without referring to molecular methods like Polymerase Chain Reaction; therefore, low-level infections with protozoa could have gone undetected.