Introduction

The cattle egret (Bubulcus ibis) is a bird with wide geographic distribution and belongs to the family Ardeidae (^{SHELDON, 1987}). In the delta region of Egypt, several bird species have been recorded, including cattle egrets (^{GOODMAN et al., 1989}). Due to cattle egret overpopulation and extensive spreading in the Egyptian delta, it has been categorized on the black list of invasive species (ESER, 2009).

Paratanaisia spp. (^{SANTOS, 1934}; ^{FREITAS, 1959}) are digenetic trematodes that inhabit the kidneys of birds. The geographical distribution of the parasite seems to be restricted to the American continent and the Philippines (^{TRAVASSOS et al. 1969}, ^{FEDYNICH et al., 1996}). Infected hosts show mild gross and microscopic lesions in the infected kidneys (^{SANTOS, 1934}; ^{MENEZES et al., 2001}; ^{PINTO et al., 2004}), while ^{Luppi et al. (2007)} reported granulomatous glomerulonephritis in psittacine birds, caused by P. bragai. In this report, we present the first record of pathological features caused byParatanaisia spp. in the kidney of cattle egrets in Kafr Elsheikh governorate, Northern Nile Delta, Egypt.

A cattle egret (Bubulcus ibis) was sacrificed and subjected to necropsy and histopathological examination. Samples from different organs were immediately fixed in 10% neutral formalin and then routinely processed for paraffin embedding. Sections of thickness 4 µm were stained with hematoxylin and eosin and examined microscopically.

The bird showed emaciation, dissipation and inability to fly. Grossly, most of the organs were within the normal limits, except for the right kidney, which showed enlargement and brownish discoloration. Microscopically, a digenetic trematode helminth was observed, consistent with Paratanaisia spp. Brown eggs, some of them containing fully developed embryos, were also noticed. The main parasite burden was within the major collecting tubules, which demonstrated severe dilatation. Some eggs and developed miracidium were found outside the parasites, attached to the lining epithelium, leading to marked hyperplasia and subepithelial mononuclear cell infiltration (Figure 1A). Some of the Paratanaisia eggs were noticed invading subepithelially or deeply into the interstitial renal tissue, which was surrounded with mononuclear inflammatory cell infiltration (Figure 1B). Some of the fully embryonated eggs and developed miracidium were seen to have extended their invasion to be intravascular (Figure 1C). The affected kidney also showed tubular degeneration, intraluminal eosinophilic hyaline casts and brown hemosiderin pigment within the lining of the tubular epithelium.

Figure 1. Photomicrographs of the lesions caused byParatanaisia spp. infection in a cattle egret. A) Cross-section through kidney showing dilated collecting tubules in a part of the trematode section and parasite eggs along the renal tubular epithelium. H&E, scale bar = 50 µm; B) Kidney showing presence of parasite eggs interstitially (arrowhead) with mild inflammatory reaction and minor connective tissue proliferation. H&E, scale bar = 100 µm; C) Kidney showing intravascular presence of fully embryonated eggs and hatched miracidium leaving empty egg shell (arrowhead). H&E, scale bar = 100 µm. 

It is well known that Paratanaisia spp. were previously reported parasitizing the kidneys of pigeons, chickens, turkeys, spot-winged quails, guinea fowls (^{MENEZES et al., 2001}) and whistling-ducks (^{FEDYNICH et al., 1996}) and that they could be a cause of death in infected birds (^{ARNIZAUT et al., 1992}).

The results represented here indicate that the inflammatory reactions within the affected kidney were primarily due to invading eggs rather than the adult trematodes, which may extend to develop chronic granulomatous nephritis in psittacines, as reported by ^{Luppi et al. (2007)}. The hyperplasia of the renal tubular epithelium and sub epithelial inflammatory cell infiltration were caused mainly by adult tegument scales and presence of free eggs.

In conclusion, as far as we know, the cattle egret is a new host forParatanaisia spp. and the pathological findings indicate that their eggs have pathogenic potential.