Parasites compete with their hosts for resources; it has been evidenced that parasites affect host population growth and regulation, spatial distribution, individual reproductive success and sexual selection. Prevalence of parasitic infections provide a first approach to understand the impact of parasites on a natural population (Amo et al. 2005). Parasitic infection is usually inferred indirectly by measuring the types and abundance of parasites present in a host population. Three metrics are commonly used to quantify infection: diversity, prevalence and intensity (Shaw et al. 2018).
This study investigated the presence of gastrointestinal parasites in captive and wild free roaming Iguana iguana in Trinidad and Tobago using coproparasitological examination. It further provided information on the diversity and prevalence of parasites and noted the difference in parasite burden with respect to sex and status (captive or wild caught) using the non-invasive method of faecal flotation.
This study demonstrated that the Green iguana in Trinidad and Tobago was host to a number of endoparasites. It further showed that no particular type of endoparasite was found exclusively within the captive or wild populations, nor was there a difference between the sexes of the local Green iguana.
The sample populations of Iguana iguana from this study demonstrated two nematodes; oxyurids and ascarids and one cestode (tapeworm). Nematode presence is fairly common in Iguanids being identified in recent studies conducted on the Blue Iguana (Cyclura lewisi) in the Grand Cayman Islands (Maurer et al. 2020) and the Green iguana (Iguana iguana) in Piauí, Brazil (Otávio et al. 2018). Like these studies nematodes were one of the most common gastrointestinal parasites found in this research. Unlike Maurer et al’s 2020 study however, this study was unable to identify trichomonads, and amoebae which were also identified in the faecal samples of the Caribbean Blue iguana.
The majority of the population regardless of sex, or captive vs wild status showed only one type of nematode parasite egg present, most of these were identified as oxyurids, and the remainder were ascarids. A high Oxyuridae presence was also found in (Amaral et al. 2021) captive leopard geckoes study with 93,3% of the samples presenting oxyurid eggs and in (Otávio et al. 2018)’s wild I. iguana studies. No clinical signs of gastrointestinal endoparasitism was noted in this study and this may be due to pinworms being described as less pathogenic nematodes and commonly existing in reptiles in large numbers (Machin 2015).
For those species with two egg parasite species coexisting oxyurids and ascarids were often seen in the sample population. Previous work though dated on various reptiles in Trinidad, demonstrated the presence of various nematodes and a cestode in other local lizards such as the South American ground lizard (Ameiba ameiva) and a single nematode family in the Golden Tegu (Tupinambis teguixin) (Everard 1975).
A small number of the sample iguana population also demonstrated eggs from the phylum Platyhelminthes, specifically tapeworm eggs which were also very few (1 to 2) eggs seen in the positive samples. Reptile tapeworms, are not host specific and require one or more intermediate hosts in order to complete their life cycle (Machin 2015). Infected reptiles may be asymptomatic or show clinical signs of endoparasitism such as lethargy, anorexia, diarrhoea, debilitation and obstruction (Machin 2015). The lack of an observed effect of infection by intestinal parasites on body condition in the current study, suggests the stability of the parasite-host interactions (Amo et al. 2005) in the Green Iguana population in Trinidad and Tobago, but this will require further study to be fully supported.
It was interesting to note that mite eggs, which are not part of the gastrointestinal fauna, were found in a few of the samples. The presence of mite eggs is not an uncommon phenomena as mites are common ectoparasites of Green iguana especially Hirstiella mites (Cervone et al. 2016). Mite eggs were identified Rom et al. (2018) in twelve percent of the lizards examined inclusive of the Green iguana and Rataj et al. (2011) also demonstrated eggs of mites known as the Trombiculid mites in another lizard, the Tokay Gecko.
The mite eggs observed may have been introduced due to the environmental conditions (Machin 2015) in which the iguanas were kept, as ectoparasites such as ticks and mites are rarely found in Green iguanas (Fowler and Cubas 2001). Both samples which tested positive for mite eggs, were from iguanas kept in captivity.
Wild iguanids are able to traverse larger land spaces, consume a varied diet of their choice including their selection of water sources and carry out courting and mating rituals, all of which can expose them to a greater diversity of parasites and provides greater opportunity for parasite inoculations (Maurer et al. 2020). However, this study did not indicate a higher parasite load in comparison to captive specimens as Maurer et al’s 2020 study indiated, it was interesting to note however that the reports of ectoparasites such as mites both came from captive specimens versus the wild free roaming iguanas used in this study.
Internal and external parasites are commonly found in captive and wild caught reptiles (Šlapeta et al. 2018), and endoparasites have been found to be an important cause of disease in captive reptiles (Pasmans et al. 2008). The diversity of parasites seen in this investigation was similar for both captive and wild iguanids.
The majority of the samples that tested positive for pinworms were from wild iguanas. Pinworms are frequently present in the lower gastrointestinal tract of herbivorous reptiles such as lizards (Šlapeta et al. 2018) which includes Iguanidae. The presence of pinworms is considered to be beneficial to the host as it improves the passage of ingesta through the intestinal tract of the reptile. As such, the complete removal of pinworms may negatively affect digestion in lizards (Šlapeta et al. 2018). Most of the wild Green iguana faecal samples obtained from various locations in Trinidad and Tobago, tested positive for the presence of pinworm eggs. This high prevalence was also observed in previous studies done on wild Green iguana in Brazil (Breves et al. 2011; Brito et al. 2014; Prado et al. 2018; Teles et al. 2016) and Singapore (Kwak et al. 2020).
Parasites are a major component of all animal populations. Males and females often differ in their levels of parasite prevalence potentially leading to sex differences in the impact of parasitism on fitness (Hicks et al. 2019). In this study there was no significant relationship between parasite burden and sex was found. This is consistent with similar studies on iguanas (Amo et al. 2005; Maurer et al. 2020; Teles et al. 2016; Vrcibradic et al. 2007).
With respect to ascarids and tapeworms, all of the male samples which tested positive were kept in captivity. Whilst over seventy percent of the positive females were wild caught. This is possibly due to the fact that females in the wild dig nests, therefore exposing themselves intimately to surface and subsurface soil which is not seen with males in the wild. Additionally, female cyclic nutritional reserve depletion related to egg production and oviposition, that may have included a degree of immunosuppression, increases the chances of infection (Maurer et al. 2020). The parasite prevalence in the wild iguanids can be attributed to the variability of the host diet, availability of intermediate host and host behaviour which may have a direct effect on parasite transmission (Elmahy and Harras 2019) and the ability to cover a greater area (Maurer et al. 2020).