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Hematological Profiles During Acute and Subacute Brucellosis in Sprague-Dawley Rats Experimentally Infected with B. abortus biotype 1

Mst. Minara Khatun, Md. Ariful Islam, Byeong-Kirl Baek

Mst. Minara Khatun, Md. Ariful Islam, Byeong-Kirl Baek, Department of Veterinary Public Health, College of Veterinary Medicine, Chonbuk National University, Jeonju, Republic of Korea
Mst. Minara Khatun, Md. Ariful Islam, Department of Microbiology and Hygiene, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh, Bangladesh

Correspondence to: Mst. Minara Khatun, Department of Microbiology and Hygiene, Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh.
Email: mmkhatun@bau.edu.bd
Telephone: +88-091-67401-6 ext. 6396
Fax: +88-091-61510
Received: May 5, 2016
Revised: June 24, 2016
Accepted: June 27, 2016
Published online: September 20, 2016

ABSTRACT

AIM: The aim of this study was to assess the hematological abnormalities such as anemia, leucopenia and thromocyopenia of Sprague-Dawley (SD) rats during the course of infection.

METHODS: The SD rats were experimentally infected ip with B. abortus biotype 1 with 1×109 colony forming unit (CFU)/ml. Blood samples were collected from the rats at 0, 3, 7, 14, 21, 28, 35, 42, 60, 90 and 120 days, after infection. Hematological analysis of the blood samples were performed using an automated blood analyzer. Blood films were prepared on a microscopic slide using blood samples obtained from the uninfected control, acutely and subacutely infected SD rats. Thin blood films were stained with Wright-Giemsastain and examined under light microscope (Olympus, BX51) for observing the hematological changes at 1000X magnification.

RESULTS: Hematological analysis revealed significant decrease of WBC, RBC, HGB, HCT and PLT in the infected rats, compared to uninfected control rats (p < 0.05).The blood film of acutely infected rats was characterized by abnormal red blood cells with infiltration of macrophages. Blood film of sub-acutely infected rats was characterized by abnormally shaped red blood cells with infiltration of lymphocytes and macrophages. Blood film of uninfected control rats showed normal shape of red blood cells with very few infiltrations by neutrophils. All of the rats infected with B. abortus during acute and subacute infection manifested splenomegaly. The highest spleen weights were recorded (2.25 ± 0.12 g) at 21 days after infection (p < 0.001).

CONCLUSION: B. abortus induced hematological changes in SD rats during the acute and subacute stages of infection that could be useful for diagnosis of brucellosis in the free ranging wild rats.

Key words: Hematological profile; Brucella abortus; SD rats; Acute and subacute stage

© 2016 The Authors. Published by ACT Publishing Group Ltd.

Khatun MM, Islam MA, Baek BK. Hematological Profiles During Acute and Subacute Brucellosis in Sprague-Dawley Rats Experimentally Infected with B. abortus biotype 1. International Journal of Hematology Research 2016; 2(3): 143-148 Available from: URL: http: //www.ghrnet.org/index.php/ijhr/article/view/1710

Introduction

Brucellosis is a zoonotic disease, caused by the several species of the genus Brucella and constitutes an important public health problem in many parts of the world[1]. The disease is transmitted to animals through ingestion of aborted materials, artificial insemination with contaminated semen[2] and natural breeding with infected bulls[3]. Humans can be infected with Brucella by contact with infected animals and drinking of unpasteurized milk and milk products[4]. Brucellosis in wildlife is the most likely source of infection for humans as well as domesticated animals[5]. Rats are found to be carriers of Brucella abortus in many parts of the world[6,7]. Brucellosis is a multisystemic disease with a broad spectrum of clinical manifestations[8]. Brucellosis is an inflammatory disease that can affect all organs or systems in the body[9]. The disease also produces a variety of nonspecific hematological abnormalities. Bonemarrow and the spleen are commonly involved and such involvement may result in a hypoplastic pattern in the peripheral blood smear[10]. Reproductive failure, infertility and abortion are the main clinical manifestations of brucellosis in domesticated animals. Undulant fever, loss of weight, weakness, malaise and sweating are the common clinical symptoms of brucellosis in human patients. Hematological abnormalities including anemia, leucopenia, thrombocytopenia and pancytopenia can be encountered during the course of brucellosis[11].

Brucellosis is an infectious disease involving the lymphoproliferative system. Changes in the hematological parameters are observed in most patients, but pancytopenia is rare. Hemophagocytosis, hypersplenisms or granulomatous changes in the bone marrow may be responsible for pancytopenia occurring during brucellosis[12]. Additionally, bone marrow involvement due to simultaneous presentation of malignant diseases with brucellosis rarely leads to pancytopenia. Reports of hematological abnormalities in brucellosis have arisen from studies in humans. There are no reports concerning hematological abnormalities in rats infected with B. abortus.

MATERIALSAND METHODS

Experimental animals

Adult SD rats (n = 40) of 8-weeks of age were purchased from a SPFcommercial company (Koatech, Korea). The rats were kept in cages in an isolated animal experimental house and supplied with food and water ad libitum. The rats were handled according to the guidelines of the Chonbuk National University. All rats were free from Brucella or abnormalities before experiment.

Experimental infection

The SD rats (n = 36) were intraperitoneally inoculated with 0.1 mL saline solution containing 1 × 109 colony forming unit (CFU) of B. abortus biotype 1. The control rats (n = 4) were kept uninfected.

Clinical examination

The rectal temperature, food and water intake of the experimentally infected rats were recorded daily until two weeks of experimental infection.

Specimen collection

Specimens of blood and tissues were collected from the rats at 0, 3, 7, 14, 21, 28, 35, 42, 60, 90 and 120 days after infection. Blood samples were collected from the rats with or without anticoagulant, through aseptical cardiac puncture, under general anesthesia induced by intraperitoneal administration of 10mg/ml Zoletil. Then the rats were euthanized and specimens of spleen were collected aseptically. Spleens were weighted by an electronic balance (Tokyo, Japan) and observed for spleen enlargement.

Hematological examination

Blood samples, collected at 0, 3, 7, 14, 21, 28, 35, 42, 60, 90 and 120 days after infection, were analyzed by an automated blood counter (ABX Vet ABC Hematology Analyzer, USA). The total white blood cells (WBC), red blood cell (RBC), hemoglobin (HGB), platelets (PLT) and hematocrit (HCT) levels of the blood samples were measured.

Examination of blood films

Blood films were prepared on a microscopic slide, using blood samples obtained from the uninfected control, acutely and subacutely infected SD rats. Thin bloods films were stained with Wright-Giemsa stain, according to the standard protocol. Briefly, air-dried blood films on microscope slides were fixed in absolute methanol for at least 5 min. Staining solution I (0.3 g of Wright stain powder was dissolved in 100 mL absolute methanol) was applied for 2 min on the horizontally positioned slides. The slides were rinsed with distilled water for 30 seconds and air-dried. Staining solution II (1 g Giemsa stain powder was dissolved in 66 ml glycerol and heated to 56℃ for 90 to 120 min. After addition of 66 mL absolute methanol and thorough mixing, the solution was left at room temperature in a closed container) was applied on the horizontally positioned slides for 5 min. Then the slides were rinsed with ample amounts of water and dried in air. Finally, cover glasses were mounted on the areas of stained blood film. The stained blood films were examined under light microscope (Olympus, BX51) for observing the hematological changes at 1000× magnification.

Statistical analysis

Hematological parameters (WBC, PLT, RBC, HCT, HGB value) and spleen weight data between infected and uninfected control rats were analyzed for statistical significance by the Student t test, using Microsoft Excel 2000. Significance of all the analyses was established at p value of < 0.05.

RESULTS

Clinical Examination

The infected rats manifested fever, anorexia and weakness.The highest rectal temperature were recorded as 38 ± 0.5℃ at 3 days after infection. The rectal temperature as well as food and water intake of infected rats became normalized two weeks after infection.

Hematological findings

Total leukocyte count and platelet counts: During the acute course of infection the total WBC counts of the infected rats were either increased or decreased, as compared to the uninfected control rats. The statistically significant increase (p < 0.05) of mean WBC counts was recorded at 14 days after infection (8.25 ± 0.5×103/mm3). The highest mean value of WBC countwas recorded at 21 days after infection (8.35 ± 0.44 × 103/mm3) (p < 0.001). The mean value of WBC count sharply declined at 28 days after infection (4.65 ± 0.99 × 103/mm3) (p < 0.05) and the mean WBC counts remained almost same level at 35 and 42 days after infection (4.12 ± 0.85 and 4.02±1.8×103/mm3, respectively). A second decrease of the mean WBC counts was recorded at 60 days after infection and the value gradually decreased at 90 and 120 days after infection (2 ± 0.4 and 1.75 ± 0.26 × 103/mm3, respectively) (p < 0.001).

Platelet counts started decreasing from 3 days after infection as compared to uninfected control rats. Deceased platelets counts were also recorded at 7 and 14 days after infection (517 ± 77.08 and 511.75 ± 88.5 × 103/mm3, respectively) that were not statistically significant. However, at 21 days after infection platelet counts (475 ± 23.8 × 103/mm3) decreased significantly (p < 0.05) as compared to uninfected control rats. A sharp declined of platelet counts were recorded at 28 days after infection. The platelet counts decreased significantly (p < 0.001) from 28 days after infection until the end of the experiment.The results of total WBC and PLT counts are presented in Figure 1.

Total RBC counts: The RBC counts of infected rats at 3 and 7 days were almost similar, as compared to uninfected control rats. A significant decrease of RBC counts was recorded at 14 days (6.27 ± 0.6 × 103/mm3), after infection (p < 0.05), as compared to uninfected control rats. The RBC counts at 21, 28 and 35 days after infection were recorded as 5.51 ± 0.61, 5.46 ± 0.86 and 5.02 ± 0.95 × 103/mm3, respectively. At 42, 60, 90 and 120 days after infection, the RBC counts (4.99 ± 1.17, 4.76 ± 1.33, 4.57 ± 1.34 and 3.85 ± 1.63 × 103/mm3, respectively) were found to be significantly decreased (p < 0.001), when compared to the uninfected control rats (Figure 2).

Hematocrit count: The hematocrit value decreased significantly at 7 days (45.6%) after infection (p<0.001), when compared to the uninfected control rats. A sharp decrease of hematocrit value was recorded at 14 days after infection (40.4 %). The hematocrit values remained almost same level from 21 days (36.6%) to 60 days (34.8%) after infection. Then the hematocrit values gradually decreased from 90 days (33.7 %) to 120 days (28.7%) after infection. The hematocrit values of SD rats are presented in Figure 3.

Hemoglobin concentration

Statistically significant decrease of hemoglobin concentration was noted at 7 days after infection (16.12 ± 0.22 g/dL) (p < 0.05), as compared to the uninfected control rats. Then the mean hemoglobin concentration gradually decreased and attained the following levels at 14, 21 and 28 days after infection; 13.9 ± 0.12 and 13.92 ± 0.09, 13.1 ± 1.14 g/dL, respectively. The mean hemoglobin concentrations deceased significantly at 35 days after infection (11.27 ± 0.63 g/dL) (p < 0.001). In the infected rats the mean hemoglobin concentration continued todecrease from 35 days to 120 days after infection (Figure 4).

The results of blood film examinations

Blood film of acutely infected rat at 21 days after infection with B. abortus showed abnormal shapes of the red blood cells with extensive to moderate infiltration of inflammatory cells such as lymphocytes, neutrophils and macrophages. Blood film prepared from the rat during subacute infection at 90 days after infection with B. abortus, manifested moderate to diffuse infiltration of lymphocytes, macrophages as well as neutrophils. The blood films results from Wright-Giemsa stain at 1000X magnification in acute and subacutely infected rats, as well as uninfected control rats are shown in Figure 5.

Spleen weight and Splenomegaly

The spleen weight of rats at 0, 3, 7, 14, 21, 28, 35, 42, 60, 90 and 120 days after infection with B. abortus biotype 1 was measured (Table 1). The highest spleen weight was recorded (2.25 ± 0.12 g) at 21 days after infection (p < 0.001). All of the rats infected with B. abortus during acute and subacute infection manifested splenomegaly (Figure 6).

DISCUSSION

Infection in wildlife with B. abortus is a significant reservoir. Controlling of brucellosis in the wildlife reservoirs is important for the eradication of brucellosis in livestock as well as humans. The early detection of the disease is a prerequisite for controlling of brucellosis in the wildlife reservoirs. The knowledge of hematological profiles of B. abortus infection is essential for accurate diagnosis of brucellosis in the free ranging wildlife reservoir. Hematologic complications in the course of acute brucellosis are not rare[13,14] and usually have the form of a mild pancytopenia that is attributed to bone marrow suppression because Brucella species show an affinity for reticuloendothelial tissue. In the present study, mild to severe forms of pancytopenia were recorded in the SD, rats following experimental infection with B. abortus biotype 1. Pancytopenia was more severe in the subacute stage of infection, compared to the acute stage in our experiment. Hypersplenism can be one of the etiologies of pancytopenia[14]. When the spleen enlarges, it traps and stores an excessive number of blood cells and platelets, thereby reducing the number of blood cells and platelets in the bloodstream. This process creates a vicious cycle: the more cells and platelets the spleen traps, the larger it grows; the larger it grows, the more cells and platelets it traps. Eventually, the greatly enlarged spleen also traps normal red blood cells, destroying them along with the abnormal ones. B. abortus infection in mice has been reported to cause enlargement of the spleen[15].

Thrombocytopenia and pancytopenia are reported in human brucellosis[16,17]. In the present study, thrombocytopenia was recorded in the SD rats during the acute and subacute stages of brucellosis. The mechanisms implicated in the platelet depletion in the course of brucellosis include hemophagocytosis[18,19] and disseminated intravascular coagulation[20]. In certain cases, though, brucellosis induces a severe immune reaction in the form of hemolytic anemia and thrombocytopenia[21,22,23], sometimes even with the presence of platelet antibodies. Another mechanism that could be implicated in Brucella-attributed thrombocytopenia is granulomatous infiltration of the bone marrow in the chronic form of the disease.

Anemia is the most frequently observed hematological abnormality in brucellosis[12,24]. In the present study, the mean value of hematocrit, RBC counts, hemoglobin concentration were significantly decreased in infected rats, as compared to the uninfected control rats (p < 0.05 or p < 0.001). These changes of hematological parameters are the clear indication of anemia in the infected SD rats. In case of human anemia was detected in 48 (44%) patients with proven brucellosis[10]. Crosby et al[25] studied hematologic abnormalities in 38 patients with brucellosis. Anemia was found in 74% of patients, leukopenia in 45%, neutropenia in 21%, lymphopenia in 63%, and thrombocytopenia in 39.5%.

Lymphocytes are white blood cells important in cell-mediated (T-cells) and humoral (B-cells) immune responses and both increases and decreases in lymphocytes can be signs of disease[26]. In this experiment, the value of WBC counts significantly increased at 21 days after infection, compared to the uninfected control rats (p > 0.001). However, significant decreases of WBC counts were recorded among experimentally infected rats after 21 days of infection, throughout the experiments (p < 0.05 or p < 0.001).

Conclusions

B. abortus induced hematological changes in SD rats during the acute and subacute stages of infection which could be useful for the diagnosis of free ranging wildlife.

ACKNOWLEDGEMENTS

The authors would like to thank Dr. S. M. Boyle (Virginia Tech, USA) for editing this manuscript and Islamic Development Bank, Saudia Arabia for providing the fund.

Conflict of interest

The authors have no conflicts of interest to declare.

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Peer reviewer: Kwabena Nsiah, Department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology, UPO, Kumasi, Ghana.

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