Proliferative and inflammatory changes in the urinary bladder of female rats naturally infected with Trichosomoides crassicauda: report of 48 cases

Alterações proliferativas e inflamatórias na bexiga urinária de ratas naturalmente parasitadas por Trichosomoides crassicauda: relato de 48 casos

Proliferative and inflammatory changes in the urinary bladder of female rats naturally infected with Trichosomoides crassicauda: report of 48 cases

[Alterações proliferativas e inflamatórias na bexiga urinária de ratas naturalmente parasitadas por Trichosomoides crassicauda: relato de 48 casos]

R. Serakides, A.F.C. Ribeiro, C.M. Silva, R.L. Santos, V.A. Nunes, E.F. Nascimento

Escola de Veterinária da UFMG

Caixa Postal 567

30123-970 Belo Horizonte, MG

Recebido para publicação em 18 de fevereiro de 2000.

E-mail: [e-mail]

ABSTRACT

The objective of this report was to describe the pathological changes in the urinary bladder of female rats naturally infected with Trichosomoides crassicauda. Forty eight 5 to 8 months of age female Wistar rats were studied. At necropsy uroliths were detected in seven animals (14.6%). Among the bladders that contained the parasite only three (6.3%) did not show any significant histological change and were considered normal, but on the contrary, three (6.3%) did contain papillomas and uroliths, four (8.3%) had uroliths associated with epithelial hyperplasia ranging from moderate to severe, and the remaining (79.2%) showed variable degrees of epithelial hyperplasia and inflammation without urolithiasis. It cannot be concluded whether irritation of the epithelium by the parasite itself plays a role in the formation of papillomas. However, the absence of papillomas in animals without uroliths suggests a positive relationship between uroliths and papillomas.

Keywords: Rat, urinary bladder, Trichosomoides crassicauda, urolith, papilloma

RESUMO

O presente trabalho teve o objetivo de descrever as alterações encontradas na bexiga de ratas naturalmente parasitadas com Trichosomoides crassicauda. Foram estudadas 48 ratas Wistar com idade entre 5 e 8 meses. À necropsia, foram detectados urólitos em sete animais (14,6%). Dentre as parasitadas, somente três ratas (6,3%) não apresentavam alteração histológica, três (6,3%) apresentavam papilomas e urólitos, quatro (8,3%) tinham urólitos com hiperplasia epitelial variando de moderada a intensa e 38 ratas restantes (79,2%) apresentavam grau variável de hiperplasia epitelial e inflamação sem urolitíase. Não se pôde concluir se a irritação do epitélio desencadeada pelo parasita apresenta algum papel na indução de papiloma. No entanto, a ausência de papiloma em animais sem urolitíase sugere uma relação direta entre urólitos e papilomas.

Palavras-chave: Rato, bexiga urinária, Trichosomoides crassicauda, urólito, papiloma

INTRODUCTION

Trichosomoides crassicauda is a nematode that is found in the urinary bladder and occasionally in the ureter and renal pelvis of rats. This parasite has a direct cycle, which allows an easy spread among animals within a colony. However, animals born through caesarian section are in most of the cases not infected. Contamination occurs by ingestion of T. crassicauda embryonated eggs, which are excreted through the urine of infected animals. When the eggs reach the stomach, the larvae are released, penetrate into the stomach wall and migrate to the lungs, kidneys, ureters, and urinary bladder by the blood stream (Baker et al., 1979).

Although the life cycle is completed by eight to nine weeks after ingestion of eggs (Baker et al., 1979), the elimination of eggs through the urine starts only eight to 12 weeks after infection (Flynn, 1973). Although T. crassicauda causes epithelial hyperplasia of the urinary bladder and cystitis (Zubaidy & Majed, 1981), its association with urolithiasis and neoplasia in the urinary bladder is not clear (Baker et al., 1979).

The use of the rat (Rattus rattus) as an animal model for tumors in the urinary bladder has increased (Cohen & Lawson, 1995; Wakui et al., 1999) and T. crassicauda can be a serious problem for carcinogenesis assays (Baker et al., 1979). The parasite induces an increase in the mitotic index in the epithelium of infected bladders, which makes the epithelium more susceptible to the effects of the carcinogenic substances (Hicks et al., 1976).

The objective of this report is to describe the pathological changes in the urinary bladder of female rats naturally infected by T. crassicauda.

CASE DESCRIPTION AND DISCUSSION

Forty-eight 5-8 month-old female Wistar rats were studied. The animals received commercial rodent food (22% protein, 1.4% calcium, and 0.6% phosphorus) and water ad libitum. They were kept in plastic cages in groups of five animals per cage under a daily regime of 11 hours of light and 13 hours of darkness. At necropsy, after gross examination of the urinary system, the urinary bladder was collected, fixed in 10% formaldehyde, and embedded in paraffin. Serial sections of the urinary bladder were stained with hematoxilin and eosin, and Giemsa. The degree of hyperplasia of the transitional epithelium was classified according to Frith (1979).

Physical and chemical analyses of the uroliths were also performed. Physical analyses assessed the size, shape, color, surface, and consistency of the uroliths. For the chemical analyses, the uroliths were ground and homogenized, suspended in an acid solution (HCl 4N), incubated at 56^oC for three minutes and centrifuged (3000rpm for three minutes). The supernatant was used for analyses of urate, cystine, ammonium, and phosphate. The pellet was used for analyses of carbonate, oxalates, calcium, and magnesium. The detection of such components was performed using a colorimetric procedure following the supplier's instructions (Bioclin, Belo Horizonte, Brazil).

Seven animals (14.6%) had rounded or oval rough surfaced uroliths and ranging from 0.2 to 1.0cm in diameter (Fig. 1). The chemical analyses indicated that the uroliths were composed by oxalates, calcium, phosphate, magnesium, and ammonium. Uroliths with such chemical composition are almost always related to nutritional imbalances, either excess or deficiency of specific nutrients (Woodard & Bruss, 1982). Considering that the commercial food offered to the animals, contained higher levels of minerals and proteins when compared to the National Research Council recommendations for rats (Nutrient..., 1995), it is possible that the urolithiasis in these cases could be related to excess of those nutrients. However, it is also important to consider the possible role of T. crassicauda acting as a nucleus for uroliths development. This parasite has been incriminated as responsible for the formation of mucoid calculi since it causes an increase in the mucous secretion by the transitional epithelium of the urinary bladder (Smith, 1946).

Histologically, the presence of the parasite was confirmed in the urinary bladder of all animals. The parasite was located in the lumen or intraepithelially. Only three of the infected urinary bladders did not show any significant histologic change. Three of the infected bladders had papillomas and uroliths and four showed uroliths and epithelial hyperplasia ranging from moderate to severe. The remaining infected animals showed variable degrees of hyperplasia and inflammation in the mucosa, which was not associated to urolithiasis (Table 1).

Most of the infected bladders showed epithelial degeneration and necrosis where the parasite was attached, and focal, multifocal, or diffuse epithelial hyperplasia ranging from mild to severe (Fig. 2). These findings are similar to those described by Antonakopoulos et al. (1991). In most cases the epithelial proliferative changes were associated to a mild multifocal inflammatory process in the lamina propria characterized by the presence of lymphocytes, eosinophils, and mast cells. Only one animal showed a severe and diffuse eosinophilic inflammation.

There were polyps in the mucosa of three infected bladders. These structures formed projections into the lumen and were diagnosed as papillomas (Fig. 3). In one of these cases there was a severe squamous metaplasia with a large amount of keratin forming rounded structures with multiple layers of keratin concentrically arranged and surrounded by epithelial cells (Fig. 4).

Uroliths in laboratory animals have been implicated in the pathogenesis of neoplasias of the urinary bladder (Hicks et al., 1976), but still there is some controversy on whether or not T. crassicauda can cause such tumors. Zubaidy & Majeed (1981) examined experimentally infected rats with T. crassicauda for a short period of time and did not observe tumors in the urinary bladder or uroliths, which is not in agreement with our findings. The development of uroliths and papillomas may probably relate to the duration of the irritation, resulting from a chronic infection.

The results are in agreement with the hypothesis that T. crassicauda may induce uroliths, by serving as a nucleus, and that subsequently these uroliths may induce papillomas. From the infected rats most showed urinary bladder epithelium hyperplasia and inflammation. From the animals with parasites a limited number showed uroliths and from these animals only three had a papilloma. It cannot be concluded whether irritation of the epithelium by the parasite itself plays a role in the formation of papillomas. However, the absence of papillomas in animals without uroliths suggests a positive relationship between uroliths and papillomas.

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Publication Dates

• Publication in this collection
  05 June 2002
• Date of issue
  Apr 2001

History

• Received
  18 Feb 2000