| Vol. 98(8) November 2003 |
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Infection Rate of Babesia spp. Sporokinetes in Engorged Boophilus microplus from an Area of Enzootic Stability in the State of Minas Gerais, Brazil Vol. 98(8): 999-1002, December 2003 Maria G Quintão-Silva, Múcio FB Ribeiro*/+ Universidade de Alfenas, Alfenas, MG, Brasil *Departamento de Parasitologia, ICB, Universidade Federal de Minas Gerais, Caixa Postal 486, 31270-910 Belo Horizonte, MG, Brasil The infection rates of Babesia sporokinetes in engorged Boophilus microplus were evaluated during a 2-year period in a dairy farm located in an area of enzootic stability. Every 14 days engorged females were collected from calves and from adult animals. Ticks were incubated at 27 ± 0.5oC and 80-90% relative humidity and Babesia infection rates were determined by microscopic examination of Giemsa-stained hemolymph smears. After 52 collections, 2105 ticks were obtained, from which 982 were collected from calves and 1123 from cows. The total Babesia infection rate was 10%, however the incidence was higher (p < 0.05) in ticks collected from calves (17.5%) than in those collected from cows (3.6%). Females collected from cows showed the highest infection rates in January, March, and August, and absence of infection in April and May. Ticks feeding on calves were infected throughout the experimental period. The infection rates of engorged females collected from naturally infected calves that were artificially infested with Babesia-free-larvae of B. microplus gradually decreased until the calves were four months old. No differences were observed among infection rates of ticks collected from calves maintained under natural conditions. Key words: Babesia sp. - tick - sporokinetes - Boophilus microplus - Minas Gerais - Brazil
Babesiosis is a disease caused by intraerythrocytic protozoan parasites of the genus Babesia, which infect domestic and wild animals, transmitted by ixodid ticks. In Latin America two species, Babesia bovis and B. bigemina, infect cattle, both transmitted by the one-host tick Boophilus microplus (Alonso et al. 1992). The state of Minas Gerais, Brazil, has an area of 588,386 km2 and the population of cattle is estimated in 20,082,067 heads, corresponding to 12.2% of the national heard (Anuário Estatístico de Minas Gerais 2002). In the state, bovine babesiosis has been a limiting disease for the cattle industry (Leite & Lima 1982, Ribeiro et al. 1983), although the region has been considered an area of enzootic stability (Patarroyo et al. 1987). The main factors interfering with transmission of Babesia are the tick parasitic load on cattle and the infection rate in the ticks (Friedhoff & Smith 1981). Several reports on seasonal variation of B. microplus ticks have been published and it is known that in Minas Gerais four generations occur per year with infestations throughout the year (Magalhães 1989, Lima et al. 2000). However, little is known about infection rates of Babesia spp. in B. microplus and the studies have been carried out under laboratory conditions. The implementation of strategic control programs against B. microplus ticks associated to new management measures in raising calves have contributed to the establishment of areas of enzootic instability in some farms, increasing economic losses due to clinical cases of babesiosis. As a consequence, considerable efforts have been made to a better understanding of epidemiological aspects of babesiosis. In addition to estimation of cattle serum reactivity to B. bigemina and B. bovis, the knowledge of infestation levels and the infection rates in the ticks are essential information for a comprehensive epidemiological study on bovine babesiosis (Alonso et al. 1992). The present study had the objective to determine the infection rates of Babesia spp. in B. microplus ticks infesting calves and adult cattle, during the dry and the rainy seasons in a dairy farm located in an area of enzootic stability.
Financial support: Fundação de Amparo à Pesquisa do Estado de Minas Gerais +Corresponding author. Fax: +55-31-3499.2970. E-mail: muciobr@mono.icb.ufmg.br Received 5 June 2003 Accepted 14 October 2003 |
