Biologia, diagnóstico morfológico e molecular da infecção experimental e natural de Babesia equi (Laveran, 1901) em Boophilus microplus (Canestrini, 1887)

Abstract

The aim of the present study was to evaluate the natural and experimental infection of B. equi in nymphs and adult Boophilus microplus using optical microscopy and molecular analysis. The experimental infection was observed in nymphs, males and females of B. microplus fed on equines chronically infected with B. equi and in non fed larvae and eggs. For the experiments two equines, of not defined breed, proven to be infected with B. equi were used. The animals were infested with B. microplus larvae of generation F4 obtained from a laboratory maintained population, known to be free of Babesia spp. infection. Daily collections of ticks were realized using as starting point the ecdisys to nymph state. After the collection the hemolymph was examined and the intestine and salivary glands were dissected, smashed on glass slides for microscopy, methanol treated and stained with Giemsa. There were dissected 860 specimens (432 nymphs, 280 females and 148 males). The dissected salivary glands were divided into two parts. The first one was smashed on microscopy glass slides, stained and examined by optical microscopy for morphologic analyses. From the second part was realized DNA extraction and PCR with specific primers for the 18S rRNA. On optical microscopy of nymph hemolymph was possible to be observed the presence of kinetes with claviform aspect characteristic for the genus Babesia. In the salivary glands of B. microplus nymphs the morphology and the sequence of developmental stages of B. equi were observed initiating on day 4 after ecdysis, being possible to see in acinary cells the formation of sporoblasts and ovoid sporozoites measuring 1.5 μm of diameter and elongated sporozoites with 3.8 to 5.2μm of length and 0.8 to 1.5 μm of width. The PCR confirmed the presence of B. equi in DNA samples extracted from salivary glands of nymphs, male and female ticks as well as in larvae and eggs. To evaluate the natural infection were collected nymphs and adult B. microplus from two equines naturally infested by these ticks and naturally infected with B. equi. These horses were originated from Seropedica city in the state of Rio de Janeiro. There were dissected 324 specimens (145 nymphs, 138 females and 41 males). The proceedings with the salivary glands were identical to the previously described for the experimental infection. Of the salivary glands submitted to PCR, 70% showed to be infected with B. equi. Microscopical analysis of the salivary glands revealed the presence of sporoblast stages and the development of elongated sporozoites in acinary glands. The morphologic, morphometric and molecular analysis confirmed the experimental and natural infection of the salivary glands of nymphs and adult B. microplus with B. equi. The results of the present study show the ability of B. equi to develop in this tick species. The detection of B. equi DNA in eggs and larvae also suggests the possibility of transovarian transmission in B. microplus. The results allow to consider the tick B. microplus as a potential biologic vector of B. equi in horses from the studied region.