LEPTOSPIROSIS IN SLAUGHTERED COWS IN THE TRIANGULO MINEIRO, MINAS GERAIS: PREVALENCE, SEROLOGICAL PROFILE AND RENAL LESIONS LEPTOSPIROSE EM VACAS ABATIDAS NO TRIÂNGULO MINEIRO: PREVALÊNCIA, PERFIL SOROLÓGICO E LESÕES RENAIS

Leptospirosis is a zoonosis that affects several species of domestic and wild animals and is an important cause of economic losses in cattle in Brazil. In this study, we determined the prevalence of bovine leptospirosis in the Triângulo Mineiro region, Minas Gerais, Brazil, identified the most frequent serovars of Leptospira interrogans, and examine the renal pathological changes associated with the disease. Samples of blood serum and kidney fragments from 100 bovine females were collected in cattle abattoir. In the serological investigation 48% of the cows were positive. The serovars for which there were more reactive animals were Wolffi (24%), Hardjo (21%) and Hebdomadis (18%). Among the positive samples, 14/48 showed antibody titers greater than 1:100, and 70.83% of the seropositive animals responded to more than one Leptospira interrogans serovar. Only one farm did not have seropositive cows and in nine farms studied, six (66.66%) presented seropositive animals to the Hebdomadis serovar. At the histopathological examination, the most frequent microscopic lesions in positive animals were hyalinization (81.25%), congestion (81.25%) and hydropic degeneration (70.83%). However, these histopathological alterations were also found in kidneys of animals negative to serology, such as hyalinization (80.77%), congestion (48.07%) and hydropic degeneration (55.77%) and these findings are unrelated to positivity. Histopathological examination of the kidneys is not indicated to replace the serological diagnosis of leptospirosis, and may be used only as a complementary examination. Despite the low frequency of seropositive animals in the Triângulo Mineiro region, the disease is present in a large number of farms. Noteworthy is the high frequency of serovar Hebdomadis and it can be considered an emerging serovar in the region. The evaluation of the frequency of this serovar in other regions becomes important, and once verified should result in the recommendation of the inclusion of this serovar in the leptospirosis control.


INTRODUCTION
Leptospirosis is a high prevalence cosmopolitan anthropozoonosis, considered endemic in cattle causing economic losses due to miscarriages, placental retention, premature births, death, infertility, and decreased milk production by mastitis (JULIANO et al., 2000;TONIN et al., 2010). The disease is caused by a group of bacteria of the order Spirochetales that are distributed in two families: Spirochaetaceae and Leptospiraceae (FAINE, 1999). This last family presents two genera of which only one is pathogenic: Leptospira interrogans. The main serovar causing diseases in cattle is Hardjo (ELLIS, 2015).
Each serovar has a unique natural host being this an important characteristic of the disease (TOMICH et al., 2007). The Leptospira interrogans serovar Hardjo has as its natural hosts bovine animals, in which it can cause chronic reproductive diseases with low pathogenicity in these animals but in high prevalence (GENOVEZ, 2016).
The bacterium is lodged in the kidney after the acute phase causing asymptomatic interstitial nephritis, being eliminated in the urine to the environment for a period of up to 180 days (GENOVEZ, 2016). The lesions in cattle are very similar to those triggered in dogs in many aspects and may occur both acutely septicemic and in the form of chronic nephritis being rarely fatal (JONES; HUNT;KING, 2000).
The definitive diagnosis recommended by the OIE (World Organization for Animal Health) for leptospirosis is MAT (Microscopic Agglutination Test). Such test is serovar-specific and can be difficult to interpret because of cross-reactions between the different serovars, especially in the acute phase of the disease (FAINE, 1999). MAT specificity reduces as the infection time increases (WILLIAN;BERNARD, 1995). In addition, the test does not differentiate vaccine titers from infectious titers, which is a drawback of the test. However, it is still considered a gold standard for the diagnosis of leptospirosis.
Therefore, the paucity of information on leptospirosis in Triangulo Mineiro region, Minas Gerais (MG), Brazil inspired us to determine the prevalence of bovine leptospirosis in this region, identify the most frequent serovars of Leptospira interrogans, examine the renal pathological changes associated with the disease, and correlate these lesions with specific serovars.

MATERIAL AND METHODS
The study population comprised cattle received for slaughter at selected abattoir in Uberlândia (MG) on the pre-selected days of sampling between October 2011 and February 2012. Samples were systematically collected from slaughter line at abattoir. Blood samples from 100 adult bovine females were collected in 15 x 75 mm glass tubes, without anticoagulant and duly identified. The collected material was transported under refrigeration in isothermal box, centrifuged at 710G (Centrifugal Rotation Force -Gravity) for five minutes to obtain the serum, later stored in Eppendorf microtubes of 1,5mL and frozen at -20ºC.
In addition to blood collection, the kidneys of these same cows were collected and grossly and histopathologically examined. When there were no visible lesions, fragmentation was standardized covering the cortical and medullary regions in the middle third of the kidney. When macroscopic lesions were visualized, such as icteric, hemorrhagic kidneys, petechiae, depressed or softened white areas, a fragment of the lesion was collected for histopathological examination, in addition to the standardized fragment in the collection.
These samples of kidneys were identified and then immediately fixed in 10% formalin, processed for histological slides (TOLOSA; RODRIGUES; FREITAS NETO, 2005), and stained with Hematoxylin and Eosin. Microscopic changes were classified according to intensity in: discrete, moderate and severe and according to the type in: degenerative, inflammatory and vascular changes.
The intensity and frequency of the changes were evaluated with the Chi-squared test. The statistical analyzes were accomplished using the software Action, version 2.9. Positive and negative animals were compared to the presence or absence of microscopic and macroscopic lesions.

RESULTS
Cows from nine properties located in the Triangulo Mineiro (MG) region were used as subjects. Forty-eight (48%) animals were positive. The most frequent serovars were Wolffi (24%), Hardjo (21%) and Hebdomadis (18%) (Figure 1). Among the positive samples, 14/48 had titer greater than 1:100 (Table 1). About 70.83% of the seropositive animals reacted to more than one serovar of Leptospira interrogans. One of the properties (I) had 100% of animals tested positive and the property F had 100% negative animals. Nine properties were studied and six (66.66%) presented seropositive animals to the Hebdomadis serovar. The macroscopic lesions most frequently observed in the kidneys of the positive animals were: increase in volume, presence of renal calculi, hyperemia, hemorrhage and pallor of the organ.

DISCUSSION
In this study 48% of the cattle were positive for leptospirosis, a frequency similar to that reported by Peiter et al. (2015) of 41.53%. Prevalence of 81% was reported by Moreira et al. (2010) and Juliano et al. (2000) reported 81.9% of the positive animals, both in the state of Goiás. In the state of Mato Grosso do Sul, Figueiredo (2007) observed 98.8% of samples positive for leptospirosis. Thus, the frequency of the disease differs among the various regions studied and this variation is probably related to environmental characteristics.
The present study draws attention to the frequency of the Hebdomadis serovar (18%) which is high when compared to the study performed by Figueiredo (2007) who observed only 2.3% of seropositive animals to this serovar. The works conducted by Tonin et al. (2010) and Peiter et al. (2015) did not test for serovar Hebdomadis, evidencing the low frequency of this serovar in cattle in Brazil.
In this study, 88.88% of the rural properties presented at least one seropositive animal, whereas in the state of Paraíba Oliveira et al. (2013) observed only 18.4% of the rural properties with seropositive animals. This data indicates that the control of the disease through vaccination or even symptomatic treatment in the region studied is precarious.
The majority of the animals had low titers (100 and 200), only 3 animals (6.25%) had a titer of 400 and one animal (2.08%) presented a titer of 800. Cattle usually develop low titers of antibodies to vaccination (100 to 400) and these titers do not indicate that the animal will develop the disease and may be a serological response to the vaccine (MARQUES, 2008). In the case of the animals in this study, since the sample collection was random at the slaughterhouse, these titers probably do not refer to vaccine effects given the short postvaccination period in which the bovine animal has high titers.
Cattle can present acute septicemic form or chronic nephritic type, and in this case the surviving animals present grayish focal lesions in the renal parenchyma, sometimes invading the cortex (JONES; HUNT; KING, 2000). Therefore, the lesions reported in the present study are nonspecific.
Histopathological examination in kidneys of cattle with leptospirosis shows interstitial nephritis with hydropic degeneration of the tubule epithelial cells, as well as cylindrical and granular hyaline (GIRIO; LEMOS, 2007). Nephritis and hydropic degeneration were found in the positive animals of the present study, however, the negative animals also presented similar alterations.
The presence of inflammatory infiltrate in the kidney may be indicative of leptospirosis, but other causes should not be excluded (YERNES and KELIS, 2001). The high rate of inflammatory lesions in animals as positive interstitial nephritis and pyelonephritis (38%), may be indicative of leptospirosis. However, 40 animals negative to MAT presented nonspecific nephritis, indicating that the presence of this lesion is not exclusive of Leptospira infection. In a recently published article, the authors state that leptospirosis in cattle is not related to the urinary tract, but to the reproductive tract (LOUREIRO; LILENBAUM, 2020). In this case, the histopathological diagnosis alone is not enough to replace the serological diagnosis of leptospirosis.
It was not possible to correlate the occurrence of specific lesions with the frequency of serovars. Microscopic changes like hyalinization appear in similar proportions in several serovars as is the case of hardjo (80.95%) and wolffi (83.33%). However, it was noted that in serovar wolffi there was a higher incidence of nephritis (100%).

CONCLUSIONS
The occurrence of leptospirosis in the MAGALHÃES, G. M. et al. Triângulo Mineiro region is low when compared to other regions of Brazil, but it is present in a large number of rural properties.
Most of the cattle in this research were reagents for the Wolffi, Hardjo and Hebdomadis serovars. Wolffi and Hardjo have always been described as frequent in Brazilian herds, but Hebdomadis is not. This serovar can be considered an emerging serovar in the region.
The evaluation of the frequency of this serovar in other regions becomes important, and once verified it should result in advice for the inclusion of this serovar in the leptospirosis control. Histopathological examination of the kidneys is not indicated to replace the serological diagnosis of leptospirosis and may be used only as a complementary examination. The diagnosis can be based on serological tests, immunohistochemical and detection of the bacterium in renal tissue.