Dog Diseases: Babesia.

Babesia (synonym Nuttallia) is a genus of parasitic protists that cause the disease babesiosis in animals and humans. The parasite is transmitted by ticks and attacks red blood cells.

The protozoan responsible for Texas fever in cattle was first identified in 1888 by Romanian biologist Victor Babeş, after whom the genus of the microorganism and the disease it causes are named. The first documented case in humans did not occur until 1957 in the former Yugoslavia. Between 1982 and 2001, 200 cases of Babesia microti were reported in the US.

Although more than 100 species have been described, only a few cause infections in humans. Most cases identified in humans are caused by B. microti (sometimes called Theileria microti) and B. divergens. In animals, B. canis, B. bigemina and B. bovis cause a particularly severe form of the disease, including severe anemia. B. duncani (or Babesia WA-1) has shown high virulence in hamsters and can cause symptomatic disorders in humans. It is phylogenetically similar to B. equi and the canine pathogen B. gibsoni.

The life cycle of B. microti involves two hosts, usually a rodent and a tick. The explanation can be followed in the figure below.

Stages in the rodent. The sporozoites are introduced into the rodent's bloodstream through a tick bite. The sporozoites enter the erythrocytes, becoming trophozoites. A stage of asexual reproduction (budding) begins, releasing merozoites into the blood, most of which infect new erythrocytes. In the blood, some merozoites differentiate into male and female gametes, although these cannot be differentiated under a light microscope.

Stages in the tick (cycle A left). When a tick bites an infected rodent, the gametes fuse in the tick's intestine, giving rise to a zygote. The zygotes, in turn, become motile ookinetes that enter the tick's salivary glands. A sporogony cycle begins, resulting in new sporozoites, which can be reinjected into a rodent by the tick bite.

Stages in humans. Humans enter the cycle when they are bitten by infected ticks. Sporozoites are introduced into the blood through the bite. As in the rodent, the sporozoites enter the erythrocytes becoming trophozoites and merozoites are formed through budding. The multiplication in the blood is responsible for the clinical symptoms of the disease. Human beings are, for practical purposes, a dead end for the parasite, since the probability of the same person being bitten by another tick is very small. However, person-to-person transmission could occur through blood transfusion.

Clinical findings. Some of these signs are usually present:

• Hyperthermia
• Prostration
• Bilirubinuria
• Hemoglobinuria
• Anemia

There are dogs with Babesiosis and Proteinuria, therefore it would always be indicated to perform a smear on a suspicious dog or one that has had or has ticks. Hepatosplenomegaly may also be observed, which is due to passive congestion and hyperplasia of the mononuclear phagocytic system.

The dog may be in serious condition, which will require aggressive and urgent supportive treatment. It must be established before reaching a certain diagnosis. These dogs show a low hematocrit, pale mucous membranes with or without jaundice. In some cases petechiae may occur due to the beginning of DIC). Premortem dogs usually have respiratory failure (porcelain mucous membranes and pipe smoking). Moderate patients usually present febrile syndrome and urinary disorders (bilirubinuria, proteinuria and hemoglobinuria). Babesiosis can also present in a mild form with slight anemia and weakness, avoiding this way to the clinician.

Certainty diagnosis The diagnosis is made by observing pyriform basophilic trophozoites measuring 2.4 µm x 5 µm inside the red blood cells in blood smears.

Capillary blood smears should be performed because the accumulation of erythrocytes is greater in these vessels. A smear of peripheral blood obtained by puncture of the antebrachial cephalic vein, the external saphenous vein, etc. with a negative result, it does not rule out this pathology. For this reason, the sample must be obtained by puncture of the inner surface of the auricle, for which we must clean and then disinfect the puncture area, taking care that there are no traces of alcohol or antiseptic. Place a small drop of blood on one of the ends of the slide and with another, make a thin smear. Do not place the slide in the refrigerator, just air drying it is enough.