Horse anaplasmosis as a cause of CNS infections and the use of computed tomography as a diagnostic imaging tool to present of its cerebral form: literature review supplemented with a clinical case

Abstract

Anaplasma phagocytophilum is an intracellular bacteria that causes several non-specific symptoms (for instance, horse lying down), posing problems in differential diagnosis. Usually, symptoms appear few days after tick exposure. Less often their neurological forms are observed to be correlated with visible neuroanatomical localization, with computed tomography (CT) or magnetic resonance (MRI). The aim of this paper is to present the review of a neurological form of EGA in a horse as well as localization of hypodense cerebral changes with the use of CT. This work also describes a case of a horse suffering from anaplasmosis confirmed by positive PCR results for Anaplasma phagocytophilum from peripheral blood and cerebrospinal fluid, four months after exposure to ticks. In 30% of such cases blood smear tests showed no evidence of bacteria. Hypodense lesions were observed in the CT scan of the brain and brainstem. As demonstrated by literature in humans, anaplasmosis can be considered in differential diagnosis as a potential cause of non-specific neurological symptoms, particularly in areas endemic for anaplasmosis, where animals are exposed to contact with ticks. Possible neurological complications in horses as a result of anaplasmosis have been reported but there are no reports on the identification and diagnosis of the brain in cerebral anaplasmosis by using CT or MRI imaging tools. So far, such a diagnostic procedure in the case of tick diseases has been identified in case of humans only.

Equine Granulocytic Anaplasmosis: A Systematic Review and Meta-Analysis on Clinico-Pathological Findings, Diagnosis, and Therapeutic Management

“…In a naturally infected horse, PCR remained positive at 2 days but was negative after 28 days [ 51 ]. In the case of chronic anaplasmosis, the pathogen was detected 4 months after tick contact, so the detection period was almost equal to the one described in another experimental study, in which the pathogen persisted for at least 129 days, without any clinical or pathological abnormalities observed [ 41 , 54 ].…”

“…EGA was also reported in a case with rhabdomyolysis and in two cases with cavitary effusion, which led to cardio-respiratory compromise [ 46 , 50 ]. Despite the fact that EGA is considered an acute illness, one horse developed a fatal chronic cerebral anaplasmosis with clinical signs like loss of consciousness, strabismus, nystagmus, tachypnea, intensified gait disorders, and recumbency [ 41 ].…”

“…DNA of A. phagocytophilum can be isolated from whole blood, leukocytes, bone marrow, or fragments of the spleen [ 7 ]. In the selected publications, besides blood samples, cerebrospinal fluid, muscle tissue, pericardial fluid, and pleural effusion showed positive PCR results for A. phagocytophilum [ 41 , 46 , 50 ].…”

“…One sample was analyzed and reported positive by PCR assay that amplified 3 genes: 16S rRNA gene, ankA gene, and citrate synthase (gltA) gene (1/98; 1.02%) [5]. Besides blood samples, DNA was detected from cerebrospinal fluid (1/120; 0.83%), muscle tissue (1/120; 0.83%), pericardial fluid (1/120; 0.83%), and pleural effusion (1/120; 0.83%) [41,46,50].…”