**2. Classification**

Babesia organisms are frequently classified as large or small. Historically, *Babesia* spp. in dogs was identified by their morphological appearance in erythrocytes of blood smears (intraerythrocytic merozoite stage). Initially, all large forms measuring between 3 and 5 μm were classified as *B. canis*, whereas all small forms measuring 1–3 μm were designated as *B. gibsoni*, but molecular analysis and DNA

sequencing have revealed that there are at least three small piroplasms infecting dogs, viz. *B. gibsoni*, *B. conradae* and the recently reported "*Babesia vulpes*" [4].

In former times, on the basis of cross immunity, serological testing, vector specificity and molecular phylogeny, *Babesia canis was* categorised into three subspecies (*B. canis canis*, *B. canis rossi*, *B. canis vogeli*) [5, 6], but now these subspecies are considered as separate species [7, 8].

### **3. Prevalence**

Out of three previously considered subspecies, *Babesia rossi* is the most virulent species and occurs predominantly in southern Africa. *Babesia vogeli* is the least pathogenic species occurring in France, Australia, Japan, Brazil, South Africa and the USA and usually causes mild disease in adult dogs but severe disease in some puppies [9]. *Babesia canis* is of intermediate pathogenicity and is widespread in Europe and Asia.

*B. gibsoni*, the smaller piroplasm is prevalent mainly in the Middle East, southern Asia, Japan, North Africa and South America and is an emerging infectious disease in the USA, as well as having been detected lately in Italy, Hungary and Australia [10]. A more virulent subspecies of *B. gibsoni* has also been identified in California [11]. *Babesia microti*-like piroplasma, *B. annae* (also known as *Theileria annae*), has been found to be endemic in dogs in northwest Spain [12]. In India both *B. canis* [13, 14] and *B. gibsoni* [15, 16] are prevalent, and almost all states of the country are affected.

#### **4. Zoonotic importance**

*Babesia* species affecting dogs and/or cats are not reported to be of zoonotic importance [17]. However, dogs and cats are close companions of people and can serve as a source of infected ticks for humans [18]. Human babesiosis is a rare disease and primarily involves just two species of *Babesia*: *Babesia divergens*, a parasite of cattle in Europe, and *Babesia microti* that parasitizes small rodents in the USA.

#### **5. Transmission**

There are two hosts for transmission of *Babesia* spp., viz., invertebrate (tick) and vertebrate host. Dogs are one among the many targets of *Babesia* spp., causing canine babesiosis (formerly called canine piroplasmosis).

Hard ticks are the main vectors for *Babesia* spp. Species such as *Rhipicephalus sanguineus*, *Dermacentor* spp. and *Haemaphysalis ellipticum* can transmit the large *Babesia* of dogs, whereas *B. gibsoni* is transmitted by *Haemaphysalis bispinosa* and *Haemaphysalis longicornis*. *Babesia annae* is thought to be transmitted by *Ixodes hexagonus* [19]. Both trans-stadial and transovarial transmissions can occur, and ticks are believed to remain infective for several generations.

*Babesia* spp. undergoes the sexual conjugation and the sporogony portions of their life cycles inside the lumen of the intestine and then within the haemocoel of the tick. Then the sporozoites from the tick's salivary gland are transmitted to their new vertebrate host via a blood meal, and thereafter the protozoan life cycle is completed within the red blood cells by asexual replication (merogony), where the parasites appear as merozoites [20], which leaves the host cell and enters another red blood cell. This cycle continues for the entire life tenure of vertebrate host or

*Overview of Canine Babesiosis DOI: http://dx.doi.org/10.5772/intechopen.82243*

until the host's immune system terminates the process. However, in many countries for the last one decade, *Babesia gibsoni* infections have been reported in the absence of tick vectors. There is now convincing evidence that these cases have arisen due to biting and fighting between infected and noninfected dogs [21, 22], but these parasites are primarily transmitted through tick bites. This association arose as a by-product of the tick's adaptation to feed on blood.

The first clinical evidence of possible vertical transmission has been documented for *B. canis* [23] and *B. microti-*like spp. [24]. Although *Babesia* undergoes part of their life cycles in ticks, the merozoites circulating in the blood may be transmitted to a healthy host directly by blood transfusion. This scenario has been described for *B. gibsoni* infection [25] and by direct contact between dogs through wounds (fighting dogs), saliva or blood ingestion [21, 22, 26].

### **6. Clinical signs and pathogenesis**

Dogs of all ages can be affected with *Babesia* spp., but young puppies are more commonly affected. The incubation period varies from 10 to 21 days for *B. canis* and 14–28 days for *B. gibsoni*. Mortality for *Babesia* spp. infections ranges from 12% for *B. rossi* to approximately 1% for *B. vogeli* [19].

The most predominant feature of babesiosis in infected dogs are haemolytic anaemia and thrombocytopenia. Multiple causes like extra- and intravascular haemolysis, RBC destruction due to increased osmotic fragility, shortened life span of RBCs, erythrophagocytosis and immune-mediated destruction of RBCs because of parasitic antigens, parasite-induced membrane damage and possibly other membrane-associated antigens leads to anaemia [27–29]. Impaired haemoglobin function, oxidative damage, sludging and sequestration of erythrocytes also likely occur [27, 28, 30].

Recent study revealed about the renal involvement in babesiosis. Hypoxaemia, glomerulonephritis and haemoglobinuric nephropathy are considered possible mechanisms and supported by histological studies [31]*.*

Pancreatitis is frequently associated with other complications and has a mortality rate of 20%. Common finding includes vomition, melaena, icterus, abdominal pain and diarrhoea. In addition, 65% of the dogs with pancreatitis also had icterus, 30% had acute respiratory distress syndrome (ARDS), 30% had immune-mediated red blood cell destruction (IMHA), and 15% had acute renal failure (ARF), while 10% had haemoconcentration, and another 10% had cerebral syndrome. It is postulated that pancreatitis is formerly described "gut" form of babesiosis [32].

The severe form of disease is characterised by marked haemolytic anaemia and acid–base abnormalities [33] with secondary multiple organ failure and complications such as ARF, hepatopathy, hypoglycaemia [34], ARDS, IMHA and cerebral pathology [35]. Small subset of dogs presents with high haematocrits (relative haemoconcentration), despite vigorous haemolysis, due to shifting of fluid from intravascular to extravascular component. These dogs are at increased risk of developing ARF or cerebral complications, as well as other organ failures [36].

The severity of the disease depends on the species of *Babesia*, presence of concurrent infections, age and immune status of the host. The disease presentation varies widely from peracute to chronic or even subclinical. *Babesia rossi*, the dominant species found in South Africa, is very virulent and causes peracute and acute disease. Most common signs include fever, anorexia, weakness, depression, pale mucous membranes, tachycardia, tachypnoea and splenomegaly. Clinical signs are because of tissue hypoxia following anaemia and a concomitant systemic inflammatory response syndrome caused by marked cytokine release [19].

*Babesia vogeli* causes clinically inapparent infection in mature dogs. The parasitaemia is very low, and infection may be missed while routine examination of blood smear. Subclinical infections are common in adult dogs, but puppies tend to present with marked anaemia [37]. It is endemic in greyhound kennels in the USA, and particular care should be taken when relocating greyhounds that can harbour subclinical infections.

*Babesia canis* infections result in a more variable pathogenicity, intermediate between *B. rossi* and *B.vogeli*. Anaemia is reported in majority of dogs and thrombocytopenia in all cases [38].

*Babesia gibsoni* infection follows either hyperacute, acute or chronic course. Among these acute course is the most common and is characterised by fever, lethargy, haemolytic anaemia, thrombocytopenia, lymphadenopathy and splenomegaly [39]. The hyperacute state is rare and is characterised by shock and extensive tissue damage. Mostly a disease of American Pit Bull and Staffordshire Bull Terriers is transmitted via dog bites [21]. In Australia and the USA, subclinical *B. gibsoni* infections have been reported, where they are PCR positive, but neither show clinical illness nor microscopic parasitaemia [40]. Such cases can have dire consequences if imported into non-endemic areas.

*Babesia conradae* is considered to be more pathogenic than *B. gibsoni*, resulting in higher parasitaemias and more severe anaemia [11].

#### **6.1 Cardiac dysfunction**

It's a rare complication of canine babesiosis; reported macroscopic cardiac lesions are effusions in pericardium, epicardial and endocardial haemorrhage involving one or more chambers with left ventricle being most commonly affected. Histopathological changes include necrosis, haemorrhage, fibrin micro-thrombi in the myocardium and inflammation. Lesions may be multifocal, but more generally they are limited to one area within the myocardium [41].

#### **6.2 Consequence of canine babesiosis**

Complicated babesiosis involves clinical manifestations that are not related to haemolytic disease. The most commonly documented complications include coagulopathy, ARF, ARDS, icterus and hepatopathy, haemoconcentration, immunemediated haemolytic anaemia (IMHA), pancreatitis, hypotension, myocardial pathology, cerebral babesiosis and shock. Rare complications include gastrointestinal disturbance, myalgia, ocular involvement, upper respiratory signs, necrosis of the extremities and fluid accumulation. These complications can overlap.

#### **7. Diagnosis**

A precise and fast diagnosis and prompt treatment is required in critical situations such as hyperacute to acute phase of *B. canis* infection, where high mortality is generally reported.

#### **7.1 Direct (microscopic) examination**

Historically, *Babesia* infection in dogs was identified based on the morphologic appearance of the parasite in the erythrocyte; thus, microscopic evaluation for detecting intraerythrocytic parasites in Giemsa or Wright's stained blood smears remains the simplest, most accessible and reasonably sensitive especially during

*Overview of Canine Babesiosis DOI: http://dx.doi.org/10.5772/intechopen.82243*

acute infections. Differentiation between large and small piroplasms is also relatively simple. Moreover, in many parts of the developing world where babesiosis is endemic, microscopy is still the only viable available option. The likelihood of spotting a piroplasm increases with proper sampling technique, viz. sampling from capillary beds (ear tip, toe nail) or examination of cells from beneath the buffy coat of a haematocrit tube [37, 42] or search along the periphery of the blood smear, as parasitized red blood cells tend to marginate while making the smear. For diagnosis of large forms of *Babesia* (e.g. *B. canis*) from the majority of sick dogs, light microscopy is highly specific [2, 43], but small piroplasms (*B. gibsoni*, *B. microti*-like sp.) are hard to observe by light microscopy, which has a relatively poor to moderate sensitivity [44], and expertise is needed. Moreover due to very low, often intermittent parasitaemias, identification of piroplasms in chronically infected and carrier dogs remains a significant challenge.

Diagnosis is more problematic in chronic cases of infection due to less virulent species such as *B. canis* and *B. vogeli*, where parasitaemia may be below the microscopic detection limit, and in such cases thick smears (not alcohol fixed) may be helpful in detecting the parasite.

#### **7.2 Haematological changes**

The major haematological changes include mild to moderately regenerative normocytic and normochromic anaemia, leucocytosis with normal to decreased neutrophil counts and most consistent finding thrombocytopenia which is severe in the acute phase of infection [45].

#### **7.3 Coagulation profiles**

In a recent study, it was reported that there is significantly lower mean platelet count, prolonged activated partial thromboplastin time, higher fibrinogen concentrations and D-dimer value in infected dogs as compared to healthy controls [46].

#### **7.4 Biochemical abnormalities**

Elevation of liver enzymes such as ALP, ALT and AST. Elevated serum bilirubin concentration is associated with degree and rapidity of the anaemia and accompanying hepatopathy. There will be low total serum protein and albumin level in dogs with babesiosis. Urea is disproportionately raised to creatinine, and this is probably due to increased urea production resulting from gastrointestinal haemorrhage or protein catabolism as a result of febrile inflammatory illness [47, 48]. In complicated cases with renal dysfunction, there will be proportionate increase in serum urea and creatinine levels indicating decreased renal perfusion, as a result of hypovolaemia, decreased blood pressure and/or decreased myocardial function. Hypokalaemia has been reported in severely affected dog, it has not connected directly with babesiosis, and this could be attributed to decreased potassium intake. Considerable elevation of positive acute phase protein (α1-acid glycoprotein) has been reported in dogs with *B. rossi* infection, but levels do not correlate with severity of disease or outcome [49].

#### **7.5 Metabolic abnormalities**

The most common complication is hypoglycaemia and is often associated with severe anaemia, icterus, young age (<6 months) and collapse [50]. Reduced survival has been associated with hypoglycaemia (<59.4 mg/dL) and hyperlactataemia. Hypoglycaemia-induced central nervous system signs should not be misdiagnosed as cerebral babesiosis.

## **7.6 Electrocardiogram (ECG findings)**

In canine babesiosis, variety of arrhythmias are reported including sinus arrest, sinoatrial block, first- and second-degree atrioventricular block, ventricular tachycardia and ventricular premature depolarizations. ECG abnormalities include prolonged QRS interval, low amplitude and notching of R waves, ST segment deviation and large T waves [41].
