Form and Function

Babesia canis is a cunning and well adapted parasite that has evolved in one of the most intelligent ways possible. This includes its relationship with the tick vector as well as the vertebrate host, primarily the dog. These relationships have aided in the movement, or transportation of this extremely well adapted species. B. canis has also formed special adaptations of structure that are unique to the many stages of its life cycle.

Specialized Structures
            B. canis has developed many specialized structures that fit certain functions. While B. canis is within the tick vector in sporozoite form, it will undergo further development and turn into a gametocyte. These gametocytes have elongated bodies that have arrowhead shaped rays characterize B. canis gametocytes, and are often called the “raybodies”. These rays aid in the fusing into tick lumen, or intestine, within the digestive tract. Once fused, the gametocyte will develop into a zygote which has an arrow-shaped organelle which releases enzymes that allow the zygote lyse through the digestive tract (Mehlhorn and Schein. 1984).

Motile Stages for Transmission
            B. canis has two motile stages within its life cycle. During true transmission from vector to host, B. canis must be in sporozoite form. All other parts of B. canis’s life cycle will deteriorate during transmission. However, when B. canis is within the tick vector it has many different stages that are mobile, each with a specific purpose. These include ookinets, and sporokinetes. Ookinetes, products of meiosis of the zygotic stage, are used to invade other tissues beside the digestive tract of the tick. Ookinetes, in order to undergo further development into sporozoites within the salivary gland, must first become sporokinetes (Melhorn and Schein 1984, Schein et al. 1980).
Adaptation for Lower impact in Host and Vector
            B. canis is a very well adapted organism. In fact, B. canis has evolved to have the lowest negative impact on both vector and host bodies. It seems that B. canis understands that if it were to heavily parasitize either the host or the vector, that it as a population would suffer greatly. Thus B. canis strives to stay at a low quantity within the host and vector. Though staying at a low quantity aMerozoites, within vectornd still surviving within a host who’s immune system does not want to it to be there is difficult. The host receives no benefit by having B. canis within itself. This is important as the vector and host is key to the transmission and thus the survival of B. canis within a given ecosystem (Chauvin et al. 2009).






Transovarial and Transstadial Transmission
            Two huge adaptations for B. canis are Transovarial and Transstadial Transmission. Transovarial Transmission occurs while B. canis is within the tick in ookinetes form, in which the ookinetes infect the eggs of a female tick. This allows B. canis to live and be spread to hosts throughout the entire lifecycle of the tick, from conception to death. This combined with the Transstadial transmission is a huge advantage for B. canis. Transstadial Transmission occurs if transovarial transmission does not occur. Transstadial, like transovarial transmission, involve B. canis being present at every stage of the tick’s lifecycle. Thus allowing B. canis to be present during the reproduction stage of the tick’s lifecycle (allows transovarial transmission to take place from this time on in females)(Young and Morzaria 1986, Joyner et al. 1963).

To learn more about other oraganism that feed off of the erythrocytes of other mammals, check out these other pages , Pediculus humanus, Anopheles earlei, and Ixodes scapularis.

Immune Response of Host
            An immune response in the canine host is caused by the injection of B. canis sporozoites via tick blood meal. This response is intensified as the sporozoites and the later merozoites divide through binary fission. Though some dog breeds are more resistant then others. It was found that the dog bread has a correlation to the resistance of B. canis. BFox Terriereagles, Fox Terriers, Dachshunds, and Mongrels are more resistant to B. canis. Where as Spaniels, Griffons, Yorkshires Terrier, and Doberman are less resistant. Though, once infected, if the dog is treated and is able to rid itself of B. canis, the dog is able to halt all forms of later infection (sterilizing immunity) (Martinod et al. 1986, Brandao et al. 2003).

The canine host was once able to combat B. canis naturally with the use of Bc28 proteins, however Bc28 is a very polymorphic antigen, and B. canis has evolved since to become resistant to it. Though further research has taken place and researchers have found that a merozoite surface antigen (found in those dog breads that are semi resistant to B. canis) has been found to prevent merozoites from being able to lyse erythrocytes of the host, thus      preventing any further spread of B. canis. This will hopefully prove to be a vaccine against B. canis in the near future (Carcy et al. 2006).

Immune response of Vector
            The tick vector is highly involved in the B. canis lifecycle. That being said, the Tick does not benefit by having a parasite such as B. canis within it. To counteract the B. canis, the tick has developed multiple methods to counter, and destroy B. canis cells. The two methods that are known to date are Longicine, and Longipain (Tsuji et al. 2007, Tsuji et al. 2008).Rhipicephalus sanguineus

Longicine is an antimicrobial peptide that is secreted into the tick digestive system where it adheres the membranes of merozoites (not common in the life cycle of B. canis while within the tick) and inhibits the proliferation of the parasite and kills it (Tsuji et al. 2007).   

Longipain is rather similar to Longicine, though it is part of a network of enzymes. Longipain like Longicine will attack merozoites while within the tick but can be found in the mid-gut of the tick, and may adhere to the lumen of the digestive tract. Longipain does this by attacking B. canis in vitro by adhering to the membrane of B. canis (Tsuji et al. 2008).                                                                      


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