Estudo experimental da infecção por Borrelia anserina em galinhas domésticas (Gallus gallus domesticus): caracterização clínica, molecular e patológica

Abstract

Avian borreliosis is an acute and septicemic disease that can affect a variety of avian species and is caused by the bacterium Borrelia anserina. It is an extremely mobile spirochete and can be detected in the blood plasma of sick fowls during the acute phase of the disease. The vector responsible for the transmission is the Argas (Persicargas) miniatus tick. The experimental study aimed to study the evolution of B. anserina infection in domestic chickens, clinically characterizing the disease through the use of molecular and pathological techniques. A total of 38 fowls were infested with B.anserina infected third stage (N3) nymphs and for study control, two fowls were infested with B.anserina free third stage nymphs. The course of infection was evaluated for 44 days after exposure of ticks to fowls and the experimental procedures were divided into over-acute phase corresponding to day 1 to day 4 post-infection (DPI), acute (5 to 10 DPI) and subacute (14 to 44º DPI), considering the progression of the disease. In the three phases, serum samples were collected daily from 10 fowls and organ fragments during autopsy. The collected material was used in molecular, histopathological and immunohistochemical exams. In all stages, negative samples from healthy birds submitted to the same experimental conditions were analyzed. In PCR, the fowls presented positive organs for B. anserina from the 4th to the 8th DPI, especially the liver, spleen and heart, which presented larger amounts of amplified DNA for the flaB gene. As for serum samples, B. anserina DNA amplification was obtained from the 5th to the 10th DPI. Histopathological analysis revealed significant mild to severe changes and lesions in all organs studied, especially at the liver and splenic level. From the 5th DPI it was possible to detect spirochetes in the liver, kidneys, spleen and heart of infected fowls when impregnated with silver. They could be visualized in these and other tissues up to the 8th DPI, when the massive presence of spirochetes in the bone marrow and ovaries were marked and evidenced, more precisely within the ovarian follicles. Immunohistochemistry was standardized to aid the diagnosis and after performing the technique it was possible to visualize the presence of spirochetes inside vessels and macrophages in the affected renal tissue, as well as confirm the antigen-antibody reaction. Infection by B.anserina caused mild and severe macro and microscopic changes in the organs studied, especially in the liver, kidneys and spleen, and the presence of spirochetes in all tissues evaluated in the acute phase of the disease. This information confirms its septicemic character. The interaction of techniques such as clinical semiology, molecular biology and histopathology in the study of infection, more faithfully portrayed the health status of fowls and contributes to a more appropriate treatment of the disease.