Dog Babesiosis

Introduction

Babesiosis is an infectious tick-borne disease of small mammals, including dogs and cats. It also can affect people. Babesia are tiny organisms that live inside of their host's red blood cells. Babesia eventually destroy those cells, causing the infected animal to become anemic. Anemia is a condition that develops when the number of red blood cells in an animal's blood stream becomes abnormally low. Anemia – whether caused by babesiosis or some other condition - can be fatal.

Causes & Prevention

Causes of Babesiosis
Babesiosis is caused by a tiny parasite that infects the red blood cells of dogs and other mammals. Two species of this parasite have been identified in the United States: Babesia canis ("large babesia") and Babesia gibsoni ("small babesia"). Babesia organisms are transmitted to dogs in the saliva of ticks. Ticks pick up these parasites when they bite infected rodents, like mice, rats, rabbits and squirrels. The infective form of the parasite is called a "sporozoite." Sporozoites are carried in the salivary glands of ticks – especially the brown dog tick. Brown dog ticks like to live on mice and deer. When an infected tick bites a dog, it transfers the organisms into the dog through its saliva. Babesia can also enter a dog's blood stream through blood transfusions and dog bite wounds. Unborn puppies can become infected with Babesia across the placenta (this is called "transplacental transmission"), if their mother is infected during her pregnancy.

Regardless of how they get into a dog, these parasites invade its red blood cells and multiply there over an incubation period of about two weeks. During this time, they stimulate the production of "fibrin-like proteases," which cause the infected dog's red blood cells to become sticky and clump together. Eventually, the damaged red blood cells rupture. This is called "hemolysis." Hemolysis causes the contents of the red blood cells to spill into the dog's blood stream. The dog's immune system will also attack the abnormal RBC clusters that are caused by Babesia.

Prevention of Babesiosis
The best way to prevent babesiosis is to control the tick population. Ticks must remain attached to a dog for many hours before they can transfer disease to it through their saliva. Any ticks found on a dog should be physically removed as quickly as possible. Special tick-removal devices are widely available. Tweezers can also be used. Because microorganisms in the blood of ticks can be dangerous to people, gloves should be worn whenever removing ticks from dogs or other animals. Before disposing of the tick, it may be worth a call to the dog's veterinarian, to see whether the tick should be brought into the clinic for identification and determination of whether it is carrying any infectious diseases. It is best to dispose of ticks in a tightly closed container, such as a jar or a sealed plastic bag, containing a bit of rubbing alcohol or dish detergent. The container should be discarded in an outdoor garbage receptacle. Believe it or not, ticks can survive and infect other animals after being flushed down a toilet, so that is not the best disposal route.

A number of topical products that can protect dogs from being bitten by ticks are available over-the-counter or from a veterinarian. These come in liquid form, as well as in collars. Discuss these products with a veterinarian to determine whether they are appropriate and safe for use on your dog, especially if you have young children and/or other pets in the household. Outdoor tick control should include regular cutting of tall grass, brush and weeds, because this type of vegetation is a prime habitat for adult ticks. Pet-safe outdoor insecticides are also commercially available.

Potential blood donor dogs should all be screened for babesiosis before their blood is accepted for donation to a veterinary blood bank.

Special Notes
Babesia gibsoni is considered to be an emerging pathogen in North American companion dogs. It is particularly common in Greyhounds and American Pit Bull Terriers. Babesia has been detected from the deep south (Texas and Florida) to the far north (Wisconsin and Michigan), as well as in other states. Certain species and subspecies of Babesia are widespread throughout Asia, while others cause extremely severe disease throughout the South African dog population.

Symptoms & Signs

How Babesiosis Affects Dogs
How badly a dog feels when it is infected with Babesia probably depends mostly upon the extent of damage to its red blood cell supply. Dogs of any age or breed can become infected with these parasites. Dogs with severe babesiosis will be weak, tired and depressed. They will be reluctant to rise and move around and probably will lose their appetite. They may also lose weight.

Symptoms of Babesiosis
Babesiosis can cause extremely debilitating disease in some dogs. It can even be deadly. Some dogs, however, show few if any symptoms of illness. When signs are present, they can be virtually indistinguishable from the symptoms associated with anemia due to other causes. Dogs infected by Babesia often develop one or more of the following symptoms:

Weakness
Lethargy
Exercise intolerance
Reluctance to rise
Pale mucous membranes (pallor of the gums and tongue)
Ocular discharge (from the eyes)
Nasal discharge (from the nose)
Lack of appetite (inappetance; anorexia)
Weight loss
Shortness of breath
Fever
Dark urine ("port-wine" urine; hemoglobin in the urine; hemoglobinuria)
Icterus (yellowness of the skin, mucous membranes, sclerae [the tough, usually white outer surface of the eyeballs] and bodily excretions; also called "jaundice")
Discolored stool
History of tick bites
History of dog fights/bite wounds
Enlarged spleen (splenomegaly)
Enlarged lymph nodes (lymphadenomegaly)
Enlarged liver (hepatomegaly)
Disorientation
Lack of coordination (ataxia)
Collapse
Vomiting
Diarrhea
Dark, tarry stools

Dogs at Increased Risk
American Pit Bull Terriers have an increased risk of becoming infected by Babesia gibsoni. Greyhounds in the United States are at increased for infection by Babesia canis. Dogs that spend significant time outdoors in tick-infested areas, including dogs used for hunting, tracking or field trial competitions, and dogs receiving blood transfusions, dogs that are prone to fighting with other dogsand puppies born to infected mothers, also are at increased risk of developing babesiosis. Dogs that have had their spleen removed, and those that are on long-term immunosuppressive steroid drug therapy, can develop especially severe complications from Babesia, irrespective of whether they are infected before, during or after the particular therapy or procedure.

Diagnosis & Tests

How Babesiosis is Diagnosed
Babesiosis is not particularly difficult to diagnose, although the more advanced diagnostic techniques will require sending blood samples out to a specialized veterinary pathology laboratory. Standard blood work performed on dogs suspected of having babesiosis includes a complete blood count and a serum biochemistry profile. In dogs with babesiosis, the results of these tests typically reveal low numbers of circulating red blood cells (this is called a low packed cell volume [PCV], or anemia). The test results also usually show a low number of circulating platelets (thrombocytopenia) and an increase in the amount of circulating bilirubin (hyperbilirubinemia). Bilirubin is one of the break-down products of red blood cells that is released when those cells rupture. Increased levels of glucose in the blood (hyperglobulinemia) are common in dogs with chronic babesiosis. Sometimes, this is the only identifiable blood abnormality.

A stained blood smear – which is a blood sample that is streaked very thinly across a glass slide, dipped in a special stain and examined under a microscope – will show either large or small Babesia organisms that can be identified by their distinctive shapes. However, the reliability of a diagnosis based on a blood smear depends upon the experience of the person examining the slide and the randomness of how many infective organisms are present in any given sample of blood. Analysis of a urine sample may reflect elevated levels of bilirubin (bilirubinuria) and/or hemoglobin (hemoglobinuria), due to the breakdown of red blood cells.

Another blood test, called a Coombs' test, is positive in up to 85% of dogs with babesiosis. This test can be used to differentiate between various types of hemolytic anemia. "Hemolytic" means something that pertains to the rupture of red blood cells. When red blood cells break down, they release bilirubin, hemoglobin and other substances into circulation. A dog with a positive Coombs' test will need additional tests to determine why it became anemic in the first place.

Advanced testing can be done with a polymerase chain reaction (PCR) test, which usually assesses a sample of uncoagulated whole blood for the presence of the genetic material (DNA) of Babesia organisms. PCR is highly sensitive and can not only identify the microscopic Babesia parasites, but also can differentiate between their species and even subspecies. Unfortunately, PCR tests for Babesia are only available at a few places in the United States. An immunofluorescent serum antibody test (IFA) is available at some laboratories. However, it does not differentiate between Babesia species or subspecies.

Special Notes
Since babesiosis can be transmitted across the placenta from an infected mother to her unborn fetuses, it should be on the list of differentials if all or most puppies in a litter are chronically weak, lethargic and pale. If one dog in a multi-dog household or kennel situation is diagnosed with babisiosis, the other dogs in that environment should also be tested for the presence of the infective organisms.

Treatment Options

Treatment Options
Dogs with babesiosis may or may not need to be hospitalized, depending upon the severity of their disease. Any attached ticks should be removed from the animal as quickly as possible. If the dog is dehydrated, supportive care will include aggressive administration of intravenous fluids. Blood transfusions, either with whole blood or packed red blood cells, may be necessary, especially if the animal is severely anemic. Certain oral medications that can potentially clear the organism from a dog's blood stream are commercially available; they can be quite expensive. The dog's veterinarian may recommend a course of treatment with prednisone or another steroid drug. Any medication can have adverse side effects, which owners should discuss with their dog's veterinarian before treatment begins.

If a dog lives in a heavily tick-infested area, it may not be realistic to remove all ticks from the dog's immediate environment. However, supportive care and anti-tick preventative treatments can improve the dog's comfort and greatly reduce the chances of infection.

Prognosis
The prognosis for dogs with babesiosis is good, as long as the infection is detected and treated in a timely fashion. Unfortunately, dogs that develop severe anemia (a low red blood cell count) and/or thrombocytopenia (a low platelet count) can have a guarded to grave prognosis.