Prevalence and intensity of pentastomid infection in two species of snakes from northeastern Brazil

This study aimed to evaluate the infection rates of snakes by pentastomids in the semi-arid region of Brazil. Fifteen snakes (four Micrurus ibiboboca (Merrem, 1820) and eleven Philodryas nattereri Steindachner, 1870) were collected between January and April of 2005, in the municipality of Crato (07° 14’ S and 39° 24’ W), State of Ceará, Brazil. Laboratorial analysis of the respiratory tracts of the sampled snakes indicated differences in host infection rates: four individuals of P. nattereri (36.4%) were infected by Cephalobaena tetrapoda Heymons, 1922 (mean infection intensity 1.5 ± 0.28, 1-2) and three specimens (27.3%) by Raillietiella furcocerca (Diesing, 1863) (2.3 ± 1.32, 1-5). Only one individual of M. ibiboboca (25%) was infected by a non-identified species of Raillietiella sp. These are the first data on pentastomid infection in snakes in Northeastern Brazil and both snake species comprise new host records for the pentastomids. The results also indicate that the generalist parasites C. tetrapoda and R. furcocerca share their definitive hosts.


Introduction
Pentastomids are important endoparasites of the respiratory system in vertebrates.At present, about 131 species have been described (Almeida and Christoffersen, 1999) and it is estimated that some 70% of those utilize snakes as their definitive host (Storch, 1993).Most of the studies published on pentastomids are taxonomical with very few providing data on their ecology and rates of infection.This usually results from the fact that most studies are based on the autopsy of specimens from museums and serpentariums.Furthermore, geographic records are often unreliable, given that in many instances the locality given is the museum in which the specimens autopsied were deposited (Self, 1969;Riley, 1986).
The respiratory tract of the snakes was removed and the search for pentastomids was performed under a stereomicroscope.The pentastomids found were cleared in Hoyer's medium, temporarily slide-mounted and preserved in ethanol 70%, and housed in the collection of the LZ-URCA and numbered as 0157-170.
Prevalence and intensity of infection can provide a first approach to the understanding of the impact of parasitism on natural populations (Amo et al., 2005a, b).Nevertheless, the only data available for Northeastern Brazil are provided by Almeida et al. (2006) in a study of the colubrid Liophis lineatus.Furthermore, there is no data on how generalist pentastomids share different sympatric hosts.
This study aims to provide some ecological information regarding the rates of infection of two snake species from the semi-arid region of Brazil, evaluating which pentastomid species are associated to each host species studied providing data on prevalence and infection intensities in them.

Material and Methods
Snakes belonging to two species, Micrurus ibiboboca (Elapidae) and Philodryas nattereri (Colubridae), were captured in the field between January and April of 2005.Snakes were captured using standard herpetological methods, such as pitfalls and active search (Auricchio and Salomão, 2002) in the municipality of Crato, Ceará, Brazil (07° 14' S and 39° 24' W).The study area is situated in the south of the state of Ceará, Northeast of Brazil (Figure 1).The site of collection is an Environmental Protection Area (Área de Proteção Ambiental -APA) of IBAMA (the Institute for the Environment and Natural Resources).Vegetation in the study area is characterized as a "Humid Forest Complex" (pluvio-nebular tropical subperennial forest), with annual average temperatures varying between 24 and 26 °C.The wet season extends between January and May and the annual average precipitation is 1090.9mm (IPECE, 2005).The herpetofauna consists of species common to the Amazon Forest, to the Atlantic Forest, and to the 'Caatinga', some of them being endemic species (Rodrigues, 2003).
Upon collection, the snakes were euthanized with ether and their snout-vent length (SVL) measured with  Motta (1963b), Rego (1983) Kiricephalus coarctatus Dryadophis bifossatus, Aporophis lineatus, Herpetodryas carinatus, Coluber corais Sambon (1922a), Rego (1981) Porocephalus crotali Crotalus terrificus Sambon (1922a), Heymons, (1935), Rego (1981Rego ( , 1984) ) Figure  (Grandidier, 1867).Such rate is considerably lower that the one found in the present study.A similar prevalence of infection by pentastomids to that which we found in the present study was found by Martínez et al. (2000) among snakes from northeastern Argentina.The lowest prevalence of infection reported by Martínez et al., (2000) was for Eunectes notaeus Cope, 1862 (only 7%), which is lower than the lowest score reported in this study.Apart from cases where only one individual was collected, the prevalence of infection by pentastomids reported by Martínez et al. (2000) ranged from 30% to 80% of sampled individuals.The range of prevalence found in this study conforms well with Martínez et al.´s (2000) data.
Nevertheless, it is noteworthy that despite similar and different rates of infection between the present study and the studies of McAllister et al. (1993) andMartínez et al. (2000), our results are highly associated to local climatic and habitat characteristics.Furthermore, it is important to note that the mentioned authors used different sampling methods, which may result in differences in the encountered rates of infection by endoparasite communities (Haukisalmi and Henttonen 1998), given that the study of McAllister et al. (1993) was performed in another continent (with different fauna and flora) and is based on a relatively small sample size.Data from Martínez et al. (2000) on prevalence of infection represent the only (20420, 20421, 20429, 20431, 20432, 20434, 20439, 30325a-c, 30326, 30327, 30328, 30329a-c, 30330a-b), R. furcocerca (31899a-c); and material from the LZ-URCA: C. tetrapoda (0043-0044) and R. gigliolii Hett, 1924 (0099-0101).Eco-parasitological terms used in this study followed Bush et al. (1997).
Our host samples can be considered as relatively homogeneous, since all snakes were collected within a relatively short period of time.Descriptive statistics are always given as the arithmetic mean ± one standard deviation.For each pentastomid species, the number of individuals (infection intensity) was correlated with snake snout-vent length (SVL) and host sex using simple regression analyses.

Results
A total of fifteen snakes were collected during the study period, being four Micrurus ibiboboca and eleven Philodryas nattereri.The parasite species found infecting the P. nattereri were Cephalobaena tetrapoda and Raillietiella furcocerca.Micrurus ibiboboca was infected by only one non-identified species of Raillietiella sp.These specimens represent new host records for the observed species of pentastomids.
The parasites collected were adults, as the uterus of females were full of eggs and they had simple hooks with no chitinous accessories, in opposition to nymphs, which have double hooks and chitinous accessories (Riley, 1986).

Discussion
Results from the present study suggest a high prevalence of parasitic pentastomids in Philodryas nattereri and a relatively mild rate of infection for Micrurus ibiboboca, the latter being similar to the rate  et al. (2000) were obtained from collections in a different area and specimens were sampled from several localities across the northeastern region of Argentina.Therefore, the results presented in this study and by Almeida et al. (2006) represent the only ecological information available on pentastomid parasitism in snakes for Northeastern Brazil, which highlights the need for further investigations in different ecosystems in order to find patterns of prevalence and intensity of infection for ophidians in South America.

Table 1 .
Pentastomids living as parasites on snakes of Brazil.
Almeida et al. (2006) area in Northeast Brazil.C. tetrapoda found in Liophis lineatus byAlmeida et al. (2006)with prevalence 16.7% (1/6) and mean intensity 2 (1-2).The diet of the species belonging to the genera Liophis and Philodryas from the semi-arid region of Brazil is similar to the diet of individuals belonging to the same genera elsewhere in Brazil, which consists mostly of vertebrates (amphibians and lizards) 1.

Table 2 .
Epidemiological data for snakes (sample sizes in parentheses) and their respective pentastomid parasites in Northeastern Brazil.For each host species (overall and by species), the mean SVL, (range in mm), prevalence (in absolute values and proportions) and intensity of infection (mean ± one standard deviation, with range in parentheses) are presented.