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Hepatozoon species are the most abundant hemoparasites of snakes.


Biology Articles » Zoology » Herpetology » Morphologic and Morphometric Analysis of Hepatozoon spp. (Apicomplexa, Hepatozoidae) of Snakes » Discussion

Discussion
- Morphologic and Morphometric Analysis of Hepatozoon spp. (Apicomplexa, Hepatozoidae) of Snakes

The objective of the present study was to evaluate the importance of morphology and morphometry for the characterization of Hepatozoon species that parasitize snakes. The dimensions and morphology of the five Hepatozoon species analyzed are in agreement with the description reported in the literature for those species. We evaluated linear and area data of the gamonts and submitted them to multivariate analysis, which permitted us to divide the species into three different populations (Fig. 2).

In most reports on Hepatozoon parasitizing snakes, new species were described on the basis of the length and width of the gamonts and schizonts and also of oocysts, sporocysts and sporozoites (Pessoa & Biasi 1973). Also, in a recent review article it was reported that many Hepatozoon species were created by simply considering a new infected host (Smith 1996).

The literature reports that exist immature and mature gamonts and that these developmental stages could be interpreted as different species (Smith 1996). Snakes with actively merogony may present gamonts of different sizes, with more slender forms representing an immature precursor to the larger gamonts (Smith et al. 1994). In the present paper, the specimens of the five studied species were homogeneous and the differentiation between mature and immature forms was not observed.

Some reports have demonstrated that the same Hepatozoon species can infect different hosts (Hull & Camin 1960, Pessoa et al. 1971). Besides, the gamonts of a same species of Hepatozoon can present slight morphologic changes depending on the host. Pessoa et al. (1974) demonstrated that it was possible to transfer H. tupinambis of the lizard Tupinambis teguixin to the snake C. durissus terrificus. The transfer induced changes in the parasite so that in the lizard, Hepatozoon species produced erythrocyte deformations but this characteristic was gradually lost in the experimental infections.

The possibility that all of the Hepatozoon species described as parasites of terrestrial snakes, which are transmitted by mosquitoes, constitute a single species whose blood forms vary with the vertebrate host has also been discussed in the literature (Ball 1970, Pessoa et al. 1971).

The above considerations show that a controversy exists on this subject. Some investigators believe that several Hepatozoon species exist while others discuss the possibility that it is a single species presenting different morphologic patterns depending on the infected host (Smith 1996).

Our results show three different populations, supporting the hypothesis of the existence of several species of Hepatozoon that can infect different species of snakes. The parasites found in H. gigas are significantly different among themselves and the two are different from the other studied parasites.

By comparing the present results with those reported in the literature about the Hepatozoon parasites of the same snakes studied by us, we observe that disagreement exists about the determination of the species. Our results show that the gamonts of the species H. terzii, H. philodryasi and the Hepatozoon sp. of C. durissus terrificus do not differ morphologically, as shown in other reports describing these species (Sambon 1909, Carini 1910, Phisalix 1931).

We also observed different patterns when we analyzed the changes induced in the erythrocytes by the parasites. We observed that all parasites induced changes, mainly in erythrocyte length, as well as nuclear flattening (Table II) and the changes induced by H. cyclagrasi were more pronounced, with alterations of the erythrocyte and its nucleus in terms of all of the parameters studied. H. migonei induced deformity of the length and width of the erythrocyte but not in its area. This parasite also caused a complete distortion of the nucleus, changing its length, width, area, and position. H. terzii did not modify the area of the erythrocyte or of its nucleus, but induced significant modifications in their lengths and widths. Hepatozoon sp. of C. durissus terrificus induced changes involving the area and length of the erythrocyte, and also flattening of the nucleus. H. philodryasi was the species that least modified the erythrocyte. Even so, it altered its area and the width of the nucleus.

The results obtained by morphologic evaluation showed that, depending on the considered variable, such as, for instance, area and width of the parasite, we can separate five different species, whereas for another variable, such as length of the nucleus, we can differentiate only two populations (Table I). Since we believe that the individual analysis of a variable is not sufficient to characterize a species, we submitted all the data obtained for each parasite to multivariate analysis, a procedure that permitted us to characterize only three different populations (Fig. 2).

Current knowledge does not allow us to state whether H. terzii, H. philodryasi and Hepatozoon sp. of C. durissus terrificus are a single species or whether they are closely related different species. This characterization may be obtained after analysis of sporogonic and esquizogonic stages also with the use of molecular techniques for comparison of the respective DNAs. If it is proven that these are only one species, the use of morphometry, a simple and inexpensive technique, will be of fundamental importance for the characterization of Hepatozoon species. However, if subsequent studies demonstrate that the species are different, the technique used by us cannot be used for species characterization, but can only be considered as an additional methodology for the study of this group, associated with morphologic studies of other evolutionary forms of Hepatozoon spp.

In the present study we did not evaluate other evolutionary forms of the parasites, which could contribute to a differentiation of populations. However, Smith (1996) reported that Hepatozoon sp. exhibit a high degree of plasticity for many features and therefore, morphological and morphometric features of the oocysts stage must be statistically significant in order for species to be described. Recent studies have demonstrated that identification using molecular techniques may contribute to solve this problem (Wozniak et al. 1994, Smith et al. 1999).


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