Multisystemic and cerebral infection associated with Halicephalobus gingivalis in Brazilian Criollo horses.

Overview

• This study documents the first phylogenetic identification of the parasitic nematode Halicephalobus gingivalis in Brazilian Criollo horses, revealing its role in severe multisystemic and cerebral infections.
• The research highlights the clinical, pathological, and molecular characteristics of the infection, stressing its potential zoonotic importance.

Background

• Halicephalobus gingivalis is a rare parasitic nematode that infects equids (horses), cattle, and occasionally humans.
• The infection, known as halicephalosis, typically manifests as meningoencephalitis, which is inflammation of the brain and its coverings.
• Worldwide, reported cases are uncommon but often severe, leading to significant neurological impairment.

Study Context and Purpose

• This study focuses on two adult Criollo horses from Rio Grande do Sul state in Southern Brazil presenting neurological clinical signs linked to Halicephalobus gingivalis infection.
• It aims to detail the pathological findings observed, conduct molecular detection and phylogenetic analysis of the parasite, and emphasize the clinical and zoonotic importance of the disease in Brazil.

Clinical Presentation and Outcome

• Both horses showed severe neurological symptoms associated with halicephalosis, such as behavioral changes, motor deficits, or other signs indicative of central nervous system involvement.
• Due to the grave prognosis and severity of clinical signs, both animals were humanely euthanized.

Pathological Findings

• Gross Examination: Visible brain lesions were found at necropsy, supporting the neurological symptoms recorded during life.
• Additional pathological alterations were identified in non-neurological systems, specifically the kidneys and lymph nodes.
• Histopathology: Microscopic examination revealed granulomatous inflammation—a type of chronic immune response—in the brain (encephalitis), kidneys (nephritis), and lymph nodes (lymphadenitis).
• These types of lesions are consistent with prior reports of halicephalosis in both animals and humans, suggesting a pattern of multisystemic granulomatous infection.

Molecular and Phylogenetic Analysis

• Molecular diagnostics targeted the 28S ribosomal RNA (rRNA) gene, a common genetic marker used for nematode identification and phylogeny.
• The analyses confirmed the presence of Halicephalobus gingivalis DNA in the infected animals.
• Phylogenetic evaluation showed that the isolates belonged to Lineage 3 of H. gingivalis, which is known from previously characterized infections worldwide, especially in horses.
• This represents the first phylogenetic description of H. gingivalis from Brazil, indicating that the parasite’s genotypic variants are globally distributed.

Significance and Implications

• This report expands the geographic knowledge of Halicephalobus gingivalis infection to include Brazil, emphasizing the parasite’s presence in South America.
• The multisystemic granulomatous disease underscores the severity and complexity of halicephalosis, which often leads to euthanasia due to poor prognosis.
• The identification of a lineage shared with global isolates suggests that this parasite strain can infect horses in multiple regions, potentially indicating common infection sources or transmission routes.
• Significantly, as H. gingivalis can infect humans, particularly those with occupational exposure to horses or livestock, this study highlights its zoonotic potential and the need for awareness and preventive measures among veterinary and agricultural workers.

Conclusions

• The study documents severe neurological and systemic infections by Halicephalobus gingivalis in Brazilian Criollo horses, confirmed both pathologically and genetically.
• It establishes the presence of Lineage 3 H. gingivalis in Brazil for the first time, linking it to a known global phylogenetic group.
• Overall, the findings stress the importance of considering halicephalosis in differential diagnoses of equine neurological diseases and recognize its impact on animal health and possible risks to human health.