RESUMO
Bovine anaplasmosis, caused by the rickettsia Anaplasma marginale, has a worldwide distribution and is the cause of great economic losses in developing countries where it is highly endemic. Transmission is carried mainly by ixodid ticks: Dermacentor spp. and Rhipicephalus (Boophilus) spp. Mechanical transmission is important in disseminating the disease within and across herds. The relationship between the rickettsia, the host and the vector is complex. Several surface proteins (Msps) have been described with functions that span from adhesins towards the erythrocyte and tick cells to evasion of the immune system of the host through the generation of antigenic variants. Biologic transmission of A. marginale through Dermacentor ticks has been well studied but many questions are unresolved as to how this organism spreads within and across herds and little is known about the role Rhipicephalus (Boophilus) ticks play in transmission in the Americas. Mechanical transmission in the absence of ticks and lack of transmission through ticks are questions that need to be addressed. Phylogenetic studies of the rickettsia show wide antigenic and genetic mosaics which affects the design of new vaccines. In the present work we will discuss the molecular elements in the relationship between the rickettsia, the tick and the mammalian host associated to the distribution and persistence of the pathogen in nature.
Assuntos
Anaplasma marginale/genética , Anaplasmose/epidemiologia , DNA Bacteriano/genética , Anaplasma marginale/imunologia , Anaplasmose/etiologia , Animais , Antígenos de Bactérias/imunologia , Vetores Aracnídeos/microbiologia , Proteínas da Membrana Bacteriana Externa/imunologia , Bovinos , Dermacentor/microbiologia , Interações Hospedeiro-Patógeno , México/epidemiologia , Rhipicephalus/microbiologiaRESUMO
The seasonal occurrence of anaplasmosis (Anaplasma marginale) outbreaks in dairy and beef cattle was analysed for a region of Argentina (29 degrees to 31 degrees S and 58 degrees to 62 degrees W) that is free of Boophilus microplus ticks, using data collected from December 1978 to November 1995. The outbreaks were confirmed by inspection of blood smears obtained from sick or dead cattle. A total of 94 outbreaks were confirmed by inspection of blood smears obtained from sick or dead cattle. A total of 94 outbreaks were identified: 48 in beef cattle and 46 in dairy herds. The proportional seasonal distribution of outbreaks was different in beef and dairy cattle (chi-square = 15.08, P < 0.01). While no seasonal pattern of anaplasmosis outbreaks was found in dairy cattle, there was a concentration of outbreaks during the summer months (54% of the total) in beef cattle. Rural practices that are carried out more frequently on dairy than on beef cattle may have favoured iatrogenic transmission of A. marginale in the milk production system.