Current advances in detection and treatment of babesiosis

Abstract

Babesiosis is a disease with a world-wide distribution affecting many species of mammals principally cattle and man. The major impact occurs in the cattle industry where bovine babesiosis has had a huge economic effect due to loss of meat and beef production of infected animals and death. Nowadays to those costs there must be added the high cost of tick control, disease detection, prevention and treatment. In almost a century and a quarter since the first report of the disease, the truth is: there is no a safe and efficient vaccine available, there are limited chemotherapeutic choices and few low-cost, reliable and fast detection methods. Detection and treatment of babesiosis are important tools to control babesiosis. Microscopy detection methods are still the cheapest and fastest methods used to identify Babesia parasites although their sensitivity and specificity are limited. Newer immunological methods are being developed and they offer faster, more sensitive and more specific options to conventional methods, although the direct immunological diagnoses of parasite antigens in host tissues are still missing. Detection methods based on nucleic acid identification and their amplification are the most sensitive and reliable techniques available today; importantly, most of those methodologies were developed before the genomics and bioinformatics era, which leaves ample room for optimization. For years, babesiosis treatment has been based on the use of very few drugs like imidocarb or diminazene aceturate. Recently, several pharmacological compounds were developed and evaluated, offering new options to control the disease. With the complete sequence of the Babesia bovis genome and the B. bigemina genome project in progress, the post-genomic era brings a new light on the development of diagnosis methods and new chemotherapy targets. In this review, we will present the current advances in detection and treatment of babesiosis in cattle and other animals, with additional reference to several apicomplexan parasites.

Fig. (1)

The life cycle of Babesia bovis. A. A B. bovis sporozoite invades an erythrocyte and transforms into a trofozoite. B. The trofozoite in a ring shape. C. Two merozoites are generated from each trofozoite by binary fission. D. Merozoites are initially bound together resembling two pears in an acute angle. E. The mature merozoites separate before escaping the erythrocyte. F. Merozoites are liberated from the erythrocyte. Some of them will invade new erythrocytes and develop into trofozoites, while others will be picked up by adult ticks to continue their cycle in the invertebrate host. G. Sexual stages are freed from the red blood cells in the intestinal tick lumen and develop to gametocytes. H. The gametocytes transform into male and female gametes that form a zygote after fusion. I. The zygote develops into an infecting stage and penetrates the tick intestinal cells. J. Fission bodies form and from them motile kinetes develop. K. Kinetes destroy the intestinal cells, escape into the haemolymph and distribute into the different cell types and tissues, including the ovaries. L. In the ovary, embryo cells are infected by kinetes (transovarial transmission). M. When the female tick lays her eggs, the embryos are already infected. N. Hatched infected larvae attach to a bovine and the kinetes migrate to the salivary glands of the tick, where they form a sporoblast. O. Thousands of sporozoites develop from each sporoblast. P. Tick larvae feed from the bovine blood and the sporozoites are liberated with saliva into the animal’s circulatory system.

Fig. (2)

Babesia especies in various hosts and tissues. A) Babesia bigemina in bovine erythrocytes. Blood smear stained with Giemsa. B) Babesia bovis in bovine erythrocytes. Blood smear stained with Giemsa. C) Babesia microti in mouse erytrocytes. Blood smear stained with Giemsa. D) Babesia bigemina kinetes in Rhipicephalus (Boophilus) microplus haemolymph. Haemolymph smear stained with Giemsa. E) Babesia bovis in a bovine brain capillar. Histological section of brain tissue stained with Giemsa. F) Detection of antibodies against Babesia bigemina by the Indirect Fluorescent Antibody Test (IFAT). Bovine antibodies were detected by a secondary, donkey IgG anti- bovine IgG bound to Alexa-Fluor 488. Images were obtained with an objective of 100X.

Fig. (3)

Chemical structures of current and novel drugs against babesiosis.