Babesiosis is a disease of the red blood cells and results in varying degrees of hemolytic anemia (essentially destruction of the RBCs that carry oxygen to the blood). It seems to hit greyhounds extremely hard but any dog that contracts it may become severely ill. It can come on sharply (acute) or violently (peracute) though neither of these stages is common in the US...or perhaps the disease simply isn't often recognized for what it is in either of these stages. It's generally found in the subclinical stage, where there are no apparent symptoms, or the chronic stage in which the disease is well-entrenched and symptoms are obvious.
The brown dog tick, Rhipicephalus sanguineus, is the usual culprit in the transmission of babesiosis; however, transmission has also occurred by direct, blood to blood transfer in fighting dogs, and by the transfusion of infected blood. Infected bitches have been known to pass the disease to pups in the womb.
In the United States, Babesiosis canis shows up mostly in the South but it does occur in other areas.. Babesiosis gibsoni is found all over the country but most often appears in pit bull terriers.
The dogs most at risk are those brought into an endemic area. These dogs are prone to severe infection. Evidently, those that are born in an area where babesiosis is prevalent get the infection while they're still protected by the colostrum in the dam's milk and, as a result, become immune carriers.
Clinical signs include fever that comes and goes, red or orange-colored urine, loss of appetite and 'loss of condition', which in my parlance means the dog becomes too thin, his bones are more prominent, his coat is dull and there is at least some loss of muscle mass.
Because there is a foreign invader in the red blood cells, the dog's immune system will start to destroy them, adding to the destruction the babesia are causing. A drop in the platelets which aid in blood clotting can make things even worse; this is especially a problem in B. gibsoni. As if that weren't enough, the immune system may begin destroying uninfected RBCs as well. Half of all dogs with babesiosis will need transfusion. Severe inflammation is common and localized inflammation of the central nervous system can occur.
Because dogs native to areas where babesiosis is common will most likely have antibodies against the disease, a positive test has to be interpreted carefully by the vet. A positive may not mean 'active' infection. Dogs brought into these areas have to be watched or seen often enough by the vet that any infection can be caught early. Older dogs don't get the disease as often as younger ones but they are more likely to die if they do. On the other hand, younger dogs seem to get more severe infections. I'm not sure if that's conflicting information from the experts or not; it could be that older dogs are better at holding it off than young ones but not so good at dealing with it once they do become infected.
Finding the parasites in blood smears removes any doubt about whether or not the dog is infected but they may not always show up in a smear. Polymerase chain reaction tests (PCRs) are a good choice for detecting the disease since they are able to find it even when there are a low number of parasites in the blood. IFAs are also supposed to be reliable tests for the B. canis organisms.
If it's caught soon enough, Imizol is effective in treating it.
Cross infection with other tick-borne diseases is common.