Coprological survey of protostrongylid infections in antelopes from Souss-Massa National Park (Morocco)

Small lungworms (Nematoda: Protostrongylidae) are nematode parasites of a wide range of domestic and wild mammals. Two types of protostrongylids can be distinguished: the meningeal protostrongylids, which parasitize the central nervous system of multiple cervid species (Samuel et al., 2001), and the pulmonary protostrongylids, which parasitize the lower respiratory tract of many other ruminant and lagomorph species (Taylor et al., 2016). Pulmonary protostrongylid nematodes colonize the bronchi, bronchioles, and alveoli of their hosts. The adult parasite lays eggs in lung tissue, which will hatch in situ, producing larvae (first stage L1) that are coughed up, swallowed, and passed in the feces. Once in the environment, the L1 larvae infect terrestrial mollusks (snails and slugs), as intermediate hosts, in which they develop from L1 stage to L3 stage. The L3 larva then infect animals that ingest their intermediate hosts, and reach the lungs through the vascular system (Anderson, 2000).

These nematodes are not only the primary infectious agents of the classical verminous pneumonia, but they also make damaged lung tissue susceptible to secondary bacterial infections (Kaufmann, 2013). Symptoms of infection in wildlife are not visibly obvious, and differ from one host to another, and the health impacts vary from sporadic observance upon necropsy (Kabakci et al., 2007; Panayotova-Pencheva & Alexandrov, 2010) to massive associated mortality (Forrester, 1971; Demartini & Davies, 1977).

Prevalent worldwide, protostrongylids are more widely studied in domestic ruminants (Kuchboev et al., 2017; Ahmadi et al., 2018; De Macedo et al., 2020) due to our economic interest in them, than in wild fauna. In the Mediterranean basin, several studies have been conducted in free-ranging wildlife, especially from the north shore: in wild caprinae from France, Spain, Italy and Portugal (Nocture et al., 1998; Acevedo et al., 2005; Cassini et al., 2015); in lagomorphs from France, Italy and Bulgaria (Lesage et al., 2014; Sergi et al., 2018; Panayotova-Pencheva et al., 2019), and in different species of ungulates from Iberian peninsula (Morrondo et al., 2017; Figueiredo et al., 2020). By contrast, no studies of protostrongylids in wild mammals have ever been conducted on the Mediterranean south shore (North Africa), particularly in antelopes.

This study was performed to fill this gap by exploring protostrongylid infections in three endangered antelope species, which previously inhabited the desert zones of Morocco and North Africa (Loggers et al., 1992). Their reintroduction happened in 1995 at Souss-Massa National Park (SMNP) in Agadir (south of Morocco). The three species are Gazella dorcas (Linnaeus, 1788), Oryx dammah, (Cretzschmar, 1826) and Addax nasomaculatus (De Blainville, 1816). The oryx and addax were introduced from different European zoos, while dorcas gazelle was repopulated from a native wild population (Müller & Engel, 2004). These three species appear on the Red list of threatened species of the International Union for Conservation of Nature (IUCN). The dorcas gazelle is listed in the ‹‹vulnerable›› category (IUCN, 2017), the addax in the ‹‹critically endangered›› category (IUCN, 2016a), and the Scimitar-horned oryx in the ‹‹extinct in the wild›› category (IUCN, 2016b).

Our objective was to identify the protostrongylid parasite species found in these endangered antelope species, and measure the intensity of infection in each host species. We opted for non-invasive methods to complete this survey. First, we used fecal examination for qualitative (larval morphologic characterization) and quantitative (larval counting) analyses. Second, we used molecular tools (sequencing the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA (rDNA)) to identify species of isolated nematode larvae using universal primers (Gasser et al., 1993).

Approval of animal care and use committee was not required; this study did not conduct any animal experiments.

Our morphological and molecular studies revealed that these three antelope species are obviously infected by two species of protostrongylids: Muellerius capillaris and a Neostrongylus linearis.

Prevalence and intensity of infection vary among antelope species as shown previously. Compared to other studies conducted under similar conditions, such as Cassini et al. (2015), the prevalence and LPG values of Muellerius capillaris in dorcas gazelle seem to be closer to those found in ibex (Capra ibex). By contrast, LPG values for M. capillaris in addax and oryx were very low even though its prevalence is high in addax. However, with comparison to the same study, the prevalence recorded for Neostrongylus linearis in the three antelopes was higher than that recorded in the ibex, but the LPG amounts registered in antelopes were lower than that noticed in ibex, excepted for the oryx that recorded a higher LPG amount compared to the ibex.

This variation in excreted larval load (LPG) depends on many factors. The fecal larval output correlates positively with parasite burden, and is linked to intermediate host (terrestrial mollusks) abundance, which is influenced by climatic parameters (moisture and temperature). Many species of terrestrial gastropods which could be implicated in the ecology of protostrongylids have been identified in the geographical area of Souss-Massa estuaries. These include Theba subdentata meridionalis, Otala lactea, Rumina decolata, Rumina saharica, Ferussacia moreleti, Cochlicella acuta and Cochlicella Barbara (Irikov and Gerdzhikov, 2013). In addition, the specificity of parasites to their hosts is variable and may explain the high interspecific variation in infection intensity. Some stress factors could also impact larval output amounts. These may be intrinsic (physiological state: e.g. pregnancy) or environment related conditions (Cabaret et al., 1980; Díez-Baños et al., 1994). Wildlife health management doesn’t consider the health of individuals only, as in domestic fauna. It is based more on monitoring population health (Wobeser, 2007) or ecosystem health, and uses a multidisciplinary approach (Aguirre et al., 2002). Parasites have been shown to influence the dynamics of their host populations by reducing fecundity and survival (Tompkins & Begon, 1999). Under natural conditions, when animal populations are left to manage on their own, a balance is established between host populations and their specific parasites (Jacobs et al., 2015). In cases of endangered species that we have to preserve under sequestered conditions in natural reserves and parks, a dashboard of follow-up indicators including parasitic infections should be put it in place (Heard et al., 2013; Stringer & Linklater, 2014).

For wildlife conservation purposes, we have resorted to introduction, reintroduction, and translocation programs, which will impact the ecology and biodiversity of the parasites they carry (Moir et al., 2012). Dissemination of introduced parasites in new ecosystems could become a hazard to endemic potential host species (Malan et al., 1997; Leighton, 2002).

The results of this current study have become part of a dashboard of health indicators that will serve wildlife management programs in the Souss-Massa National Park for routine monitoring, or for further animal translocation operations. These studies should be extended to examinations of adult parasites in eventual cadavers to characterize adult nematodes in each antelope host, and to the infective larvae in the intermediate hosts to identify snail species implicated in the life cycle of each protostrongylid species.