Parasites of red blood cells: Babesia and Mycoplasma (Proceedings)

BABESIA

Overview

     • Protozoal disease (genus: Babesia) of dogs and cats where merozoites (piroplasms) infect RBCs

     • Degree of illness is usually dependent on the severity and rate of anemia development.

     • Anemia mainly as a result of immune mediated hemolysis but also due to direct piroplasm damage to RBCs.

Etiology/Pathophysiology

     • Infection (by tick transmission, transplacental, blood transfusion, or, in the case of B. gibsoni, by bite wounds presumably by blood from infected dog entering a bite wound.) followed by 2 week incubation period during which piroplasms infect and multiply in RBCs, resulting in RBC damage mainly from immune mediated processes but also direct RBC lysis.

     • In the case of Rhipicephalus sanguineus tick, larvae, adults and nymphs can all transmit infection; ticks need to be attached for several days; in ticks, the parasite reproduces by sexual reproduction; ticks can be infected by eating a blood meal or by transovarial means.

Dogs

     • Large (4 – 7 µm): B. canis distributed worldwide; 3 sub-species based on biologic, genetic and geographic distribution:

           o B. canisvogeli – USA, Africa, Asia, Australia. Transmitted by R. sanguineus ticks, so disease found in southeastern, southern states, and California.

           o B. canis rossi - Africa (most virulent sub-species)

           o B. canis canis – Europe, areas of Asia

           o Small (2 – 5 µm): several genetically distinct sub-species:

           o B. gibsoni – world-wide distribution (especially Asia) including the USA.

           o B. conradae – (California – genetically distinct from B. gibsoni) – infects only dogs and only reported in California.

           o B. microti-like – Spain, but recently reported in a Pit Bull terrier dog from Mississippi (unknown if this is a local case or imported).

           o Theileria annae – (Spanish dog piroplasm). Reported in Spain and Europe.

Cats

     • Small (2 – 5 µm) – B. felis reported in Africa.

Signalment/History

     • History of tick attachment.

     • History of recent dog bite wound may be a risk for B. gibsoni infection.

     • Any age or breed of dog can be infected.

     • Severity of disease – depends on the strain of the organism, and the age and breed of the animal.

     • B. canis infections - more prevalent in Greyhounds (USA).

     • B. gibsoni infections - more prevalent in American Pit Bull, Staffordshire, and Tosa Inu breeds.

Clinical Features - Dogs

     • Peracute, acute, chronic, or asymptomatic (in some carrier animals).

     • Splenectomy and immunosuppression – severely worsens disease (B. canis rossi) or makes it apparent (B. canis in the USA).

     • Immunosuppression – may result in an increase in parasitemia and manifestation of clinical signs in chronically infected dogs (B. canis in the USA).

     • Most severe disease – caused by B. gibsoni in the USA, and B. canis rossi in Africa.

     • B. canis - rarely causes clinical disease in the USA.

Signs include: Lethargy, anorexia, weight loss, fever.

     • Pale mucus membranes, icterus.

     • Splenomegaly, lymphadenopathy, hemoglobinemia/uria.

     • Gastrointestinal signs - Some dogs develop vomiting, diarrhea, dark feces (from increased bilirubin excretion).

     • Cerebral babesiosis - weakness, disorientation, collapse (B. canis rossi in Africa).

     • Renal/urologic disease – results in renal failure (B. canis rossi in Africa).

Differential Diagnosis

     • Immune mediated diseases - hemolytic anemia, ITP, idiopathic, ehrlichiosis, RMSF, neoplasia, haemobartonellosis, cytauxzoonosis, SLE.

     • Non-immune mediated diseases - hemolytic anemia; heartworm caval syndrome, zinc toxicity, splenic torsion, Heinz body anemia, DIC, PK deficiency, PFK deficiency.

     • Causes of jaundice – hepatic or post-hepatic disease (obstruction or rupture of biliary tract).

Diagnostics

CBC

     • Mild to severe (PCV < 10%) regenerative anemia.

     • Peracute – animal may present before a regenerative response has time to occur.

     • Anemia - may not be present in all cases (e.g. carriers: Greyhounds with B. canis in USA)

     • Spherocytes, autoagglutination and positive Coombs test may also be present.

     • Thrombocytopenia - usually moderate to severe, and can occur without anemia.

     • Variable leukocytosis or leukopenia.

Biochemical profile/urinalysis

     • Hyperbilirubinemia/uria – if hemolysis acute and severe (African cases rather than USA).

     • Hyperglobulinemia - common in chronic cases (sometimes the only blood chemistry abnormality in these cases).

     • Mild elevated liver enzymes - due to anemia/hypoxia.

     • Renal failure and metabolic acidosis (B. canis rossi in Africa).

     • Bilirubinuria – common.

     • Hemoglobinuria – detected less commonly in the USA than in Africa.

Other tests

     • Microscopic examination of stained thin or thick blood smears – can provide definitive diagnosis but sensitivity depends on experience of microscopist; modified Wright's stain best for viewing organism; blood from peripheral capillary (ear prick) may improve sensitivity; can not differentiate sub-species using microscopy.

     • B. canis - large piriforms within RBCs but also ring forms.

     • B. gibsoni - smaller and often single forms are found per RBC.

     • Serology – IFA; false negatives in young dogs and in some infections; does not differentiate species and sub-species; use if microscopic examination negative with high clinical suspicion of disease, but if negative, need to confirm with a PCR.

     • PCR - tests for presence of Babesia DNA in a biological sample (usually EDTA anti-coagulated whole blood), and can differentiate sub-species and species; more sensitive than microscopy.

     • A combination of serology and PCR is considered to offer the highest sensitivity.

Therapeutics

     • Anemic patients - transfusion of whole blood or packed RBCs (for loss of RBC mass).

     • Polymerized bovine hemoglobin solution. May be used if fresh blood is not available.

     • Severely affected patients require aggressive fluid therapy for hypovolemic shock from blood loss (usually as a result of thrombocytopenia with bleeding).

Drugs of choice: no drug regimen is 100% effective, so an infected dog is infected for life.

     • Imidocarb diproprionate (Imizol® , Schering-Plough) - preferred therapy; may clear B. canis infections usually but not B. gibsoni (Asia). Certainly decrease morbidity and mortality

     • Diminazine aceturate (not available in US and not FDA approved). Similar efficacy to Imazol®

     • Metronidazole, clindamycin, and doxycycline: - decrease clinical signs but do not clear infection.

     • Azithromycin – give in combination with atovaquone is preferred Tx for B. gibsoni infections.

     • Prednisone - treat immune mediated component of anemia

ERYTHROCYTIC MYCOPLASMAL INFECTIONS

Definition/Overview

     • Red blood cell destruction and anemia caused by parasite attachment to the external surface of RBCs and immune response by the host.

Etiology/Pathophysiology

     • Haemobartonella felis (cats)and Haemobartonella canis (dogs) – classified at rickettsial bacteria.

     • Recently recognized to be mycoplasmal bacteria based on genetic determinations.

     • Proposed new names:-

           o Mycoplasma haemofelis for a large form of H. felis.

           o Mycoplasma haemominutum for the small form of H. felis.

           o Mycoplasma turicensis – found on PCR only, not seen cytologically

           o Mycoplasma haemocanis for H. canis (dogs).

     • The large species of mycoplasmal organisms infecting cats – generally causes more severe disease than small species.

     • Cats – anemia more severe if FeLV infected. Splenectomy does not make disease worse.

     • Dogs – likelihood of severe anemia greatly increased if splenectomized or with pathologic changes in the spleen.

Signalment/History

     • Worldwide distribtution.

     • Most common in adult (dogs and cats).

     • More common in males cats and FIV-infected cats.

     • No sex prevalence in dogs.

Clinical Features

Cats

     • Variable disease severity – ranges from inapparent infection to marked depression and death.

     • Intermittent fever (50% of the time) during the acute phase.

     • Depression, weakness, anorexia, pale mucous membranes.

     • Splenomegaly.

     • Icterus - rare.

Dogs

     • Mild or inapparent signs – pale mucous membranes and listlessness.

     • In splenectomized dogs – signs more like cats.

Differential Diagnosis

     • Other causes of hemolytic anemia:- IMHA; babesiosis (not in cats in the U.S.); cytauxzoonosis (cats only); Heinz body hemolytic anemia; microangiopathic hemolytic anemia; pyruvate kinase deficiency; phosphofructokinase deficiency (dogs only).

     • Differentiated from IMHA – only by recognition of parasites in blood (stained blood film or PCR-based assays); both disorders may be Coombs test-positive.

     • Babesia and Cytauxzoon spp. – differ in morphology from these mycoplasmal organisms.

     • New methylene blue stains – used to identify Heinz bodies.

     • Enzyme assays or specialized DNA tests – used to diagnose pyruvate kinase and phosphofructokinase deficiencies.

Diagnostics

CBC

     • Anemia – usually with reticulocytosis if regenerative. Also anisocytosis, macrocytosis, Howell-Jolly bodies, and occasionally marked normoblastemia.

     • Anemia – may appear poorly regenerative if a precipitous decrease in PCV has occurred early in the disease or if there are other concurrent disorders (e.g., FeLV or FIV infections in cats).

     • Autoagglutination – may see in feline blood samples after they cool to below body temperature.

     • Variable total and differential leukocyte counts of little diagnostic assistance.

     • Hemoglobinemia – rarely observed, so no hemoglobinuria reported.

Biochemical profile

     • Hyperbilirubinemia – seen in some cases but seldom severe.

     • Substantial bilirubinuria – seen in some dogs.

     • Abnormalities related to anemic hypoxia or profile can be normal.

     • Hypoglycemia – possible in moribund cats (not specific to this disease).

     • Plasma protein concentrations – usually normal but may be increased.

     • Routine blood stains (e.g., Wright - Giemsa) to identify organisms in blood films; overall, low sensitivity; examine before treatment is begun as treatment increases false negatives.

     • Reticulocyte – stains can't be used as punctate reticulocytes (cats) appear similar to parasites.

     • Organisms must be differentiated from precipitated stain – refractile drying or fixation artifacts, poorly staining Howell-Jolly bodies, and basophilic stippling can confuse diagnosis.

     • Feline organisms – small blue-staining cocci, rings, or rods on RBCs.

     • Canine organisms – commonly form chains of organisms that appear as filamentous structures on the surface of RBCs.

     • Parasitemia – cyclic, and thus organisms not always identifiable in blood (especially in cats).

     • PCR-based assays (on whole blood or dry) – significantly more sensitive than cytology.

     • Direct Coombs test – may be positive.

Therapeutics

     • Without therapy – mortality with the larger form may reach 30% in cats.

     • Outpatient treatment – unless severely anemic or moribund.

     • Blood transfusions – required when the anemia is considered life-threatening.

     • IV administration of glucose-containing fluid – recommended in moribund animals.

Drugs of choice

     • Doxycycline (10mg/kg/day, PO, for 2 wks) – drugs of choice.

     • Enrofloxacin (5mg/kg/day, PO) – efficacious alternative to doxycycline.

     • Prednisolone – may be given to severely anemic animals (to treat immune mediated destruction of RBCs); gradually decrease dosage as the PCV increases.

Precautions/interactions

     • Tetracycline antibiotics – may produce fever or evidence of gastrointestinal disease in cats; use a lower dosage or a different drug, or discontinue drug therapy altogether.

     • Doxycycline – may cause esophagitis and stricture in cats; use liquid form or give with food.

     • Enrofloxacin – has been associated with blindness in cats; may cause arthropathy in young cats.

     • Chloramphenicol – may use in dogs; can cause dose-dependent erythroid hypoplasia in cats.

Comments

     • Examine animal after 1 week of treatment – to confirm that PCV has risen.

     • Alert owner – cat may remain carriers even after completion of treatment but seldom relapse with disease once PCV returns to normal.

     • Prognosis usually excellent in cats – if treated early in disease.

REFERENCES

1. Willi B, Boretti FS, Cattori V, et al: Identification, molecular characterization, and experimental transmission of a new hemoplasma isolate from a cat with hemolytic anemia in Switzerland. J Clin Microbiol 2005;43(6):2581-5.

2. Sykes JE, Drazenovich NL, Ball LM, et al: Use of conventional and real-time polymerase chain reaction to determine the epidemiology of hemoplasma infections in anemic and nonanemic cats. J Vet Intern Med 2007;21(4):685-93.

3. Tasker S, Peters IR, Papasouliotis K, et al. Description of outcomes of experimental infection with feline haemoplasmas: Copy numbers, haematology, Coombs' testing and blood glucose concentrations. Vet Microbiol 2009;139(3-4):323-332.

4. Sykes JE, Terry JC, Lindsay LL, et al: Prevalences of various hemoplasma species among cats in the United States with possible hemoplasmosis. J Am Vet Med Assoc 2008;232(3):372-9.

5. Jefferies R, Ryan UM, Jardine J, et al.Babesia gibsoni: Detection during experimental infections and after combined atovaquone and azithromycin therapy. Exp Parasitol 2007;117:115-23.

6. Irwin PJ. Canine babesiosis: from molecular taxonomy to control. Parasites & Vectors 2009;2 (S1):1-9.