Experimental infection by Anaplasma marginale in buffaloes and cattle: clinical, hematological, molecular and pathological aspects

Abstract

The study aimed to evaluate and compare the clinical, laboratory and pathological aspects of buffalo and bovine experimentally infected with AmRio 2 strain of Anaplasma marginale. Four Murrah buffaloes and four crossbred cattle were used in the experiment, which two animals of each species were splenectomized. Strain AmRio 2 of A. marginale was inoculated in all experimental animals. Clinical exams, Packed Cell Volume (PCV), blood counts, blood smears, rickettsemia, necropsy and histopathology were performed in all cases. Semi-Nested-PCR (snPCR) for the msp5 and snPCR for the msp1α target gene for identification of A. marginale in blood samples from animals was done. From positive samples for msp1α snPCR, samples were analyzed for the amino acid sequences of this gene. Two splenectomized cattle presented apathy, pale mucous membranes, jaundice, hyperthermia, and severe anemia. The remaining experimental animals did not show clinical signs. The rickettsemia in all animals was less than 1%. The mean PCV of the splenectomized cattle was below 20% at two-time points after infection. On the blood count, the main changes were observed in splenectomized calves and were characterized by a decrease in red blood cells, hemoglobin, PCV and platelets (p <0.05). All animals presented leukocyte elevation by increased lymphocytes, however, with no significant difference. The average prepatent period was two days in all the animals. The average incubation period in cattle that became ill was 25.5 days, and death occurred, on average, 63 days after inoculation of the strain. The necropsy findings were characterized by pale carcass, ascites, enlarged liver, distended gallbladder, and thick bile. Histopathological findings included infiltration of macrophages and lymphocytes in various organs, hepatic sinusoidal dilatation, and necrosis of the large intestine. In snPCR for the msp5 gene, 100% of the animals were positive in at least one evaluation. And in the snPCR for the infection of the msp1α target gene was also found in all animals in at least one sample evaluated. However, sequencing revealed only five animals, including the bovine which died, with a similarity of the amino acid sequences with AmRio 2 strain of A. marginale. It is concluded that the splenectomized cattle died due to anaplasmosis caused by the inoculated strain and the buffalo were more resistant compared to cattle. Buffaloes can be an alternative to cattle rearing in areas with a high occurrence of clinical cases of anaplasmosis.

Gross and Histopathological Findings of Naturally Occurring Anaplasma marginale Infection in Cattle

“…Congestion and haemorrhages were also observed. In overall, the histopathological changes observed in the present study are in agreement with previous reports (Jaswal et al, 2015;Abba et al, 2016;Lima et al, 2019). It is well known that anoxia causes degenerative changes and necrosis in parenchymatous organs.…”

“…The post mortem examination also revealed presence of severely congested lungs (Fig 2D ), hepatomegaly with blunt edges and necrosis (Fig 2E), splenomegaly with discoloration (Fig 2F ) and distended gall bladder with dark colored bile (Fig 2G). Pulmonary congestion, distension of gallbladder, enlargement of liver and spleen has been documented in both natural and experimental bovine anaplasmosis (Jaswal et al, 2015;Abba et al, 2016;Lima et al, 2019). Splenomegaly with congestion and discoloration reported in the present study may be due to erythrophagocytosis that results in excessive destruction of defective erythrocytes by macrophages within the spleen (Devos et al, 2006).…”