24. hemoparasites (bacteriology)

anaplasma marginale source

• infected ruminants

  • mainly, other infected cattle

  • other ruminants (including wildlife)

what is a major predisposing factor to anaplasma marginale?

age

• OLDER cattle = more severe illness

• young animals less severely affected

how is anaplasma marginale transmitted?

1. ticks → dermacentor species (main vector in U.S.)

2. biting flies

   • stable flies (stomoxys)

   • horse & deer flies (tabanus)

3. iatrogenic

   • fomites → blood-contaminated medical equipment

4. transplacental

anaplasma marginale virulence factors

• antigenic variability (evade host immune system)

• adhesins → outer membrane protein A

  • facilitate binding to host cells & uptake into both tick and mammal cells

• type 4 secretion system

  • helps invade host cells

anaplasma marginale pathogenesis

• causes hemolytic anemia

  • organism attaching to and entering RBCs → damages RBCs and decreases lifespan

  • extravascular hemolysis — RBC destruction

    • due to phagocytosis of parasitized RBCs by macrophages

where in the body does hemolysis mainly occur? (anaplasma marginale)

• primarily in the spleen (by splenic macrophages)

• also other macrophages (reticuloendothelial system)

anaplasma marginale clinical signs associated with anemia & decreased O₂ delivery

• pallor

• lethargy

• weakness

• icterus (from RBC breakdown — hemoglobin → bilirubin)

• labored breathing

other clinical signs of anaplasma marginale (cattle)

• nonspecific signs: fever, anorexia, weight loss, decreased production

• abortion

• death (severe cases)

anaplasma marginale diagnostics

• CBC → regenerative anemia suggestive

• cytologic exam of blood smear → organisms within RBCs

  • dense cocci at RBC margins

• PCR

• serology

anaplasma marginale treatment

• antimicrobials → tetracyclines

  • unlikely to eliminate carrier state

• supportive care

  • blood transfusion if severe anemia

  • maintain hydration and nutrition

anaplasma marginale prevention

• maintain anaplasma-free herds

• control ticks and biting flies

  • house in areas where ticks are less likely

• medical practices: good hygiene

  • prevent blood contamination of instruments

  • do not re-use needles when vaccinating

• vaccines not yet commercially available (in development)

is anaplasma marginale contagious? is it zoonotic?

• to other adult cattle → no; requires vector

• possible from cow to calf (transplacental)

• to humans → no; not zoonotic

• reportable in WI

mycoplasma gram stain/morphology

• gram negative

• very small

• lack cell wall

what disease does mycoplasma haemofelis cause?

hemolytic anemia in cats (“feline infectious anemia”)

hemotropic mycoplasmas (hemoplasmas) lifestyle

obligate RBC parasite

• epicellular: attach to surface of RBCs (NOT intracellular)

• requires host cell to survive

• cannot be cultured in lab

what are predisposing factors to mycoplasma haemofelis?

• male, outdoor cats

• if infected with M. haemofelis but otherwise healthy → usually asymptomatic

• clinical symptoms more likely if:

  • immune compromised (ex. FeLV or FIV infection)

  • other underlying disease

  • recent stress (ex. recent surgery, cat-bite abscess)

how is mycoplasma haemofelis transmitted?

transmission not definitively characterized

• blood sucking arthropods? (ex. fleas)

• queen to kittens (mode uncertain)

• cat bite/fight possible?

• iatrogenic → blood transfusion from carrier cat

mycoplasma haemofelis virulence factors

• adhesins → attach to RBCs

• antigenic variation

  • evade host immune system

  • contribute to cyclic increases and decreases in RBC #s

  • cyclic fever

mycoplasma haemofelis pathogenesis

hemolytic anemia

• organism attaches to RBCs → damage → decreased lifespan

• extravascular hemolysis — immune-mediated component suspected

  • RBC antigens exposed or altered

  • host makes antibodies to m. haemofelis organisms AND to parasitized RBCs

  • phagocytosis of parasitized RBCs → RBC lysis

    • by splenic macrophages

    • by other macrophages/reticuloendothelial system

mycoplasma haemofelis clinical signs

• pale mucous membranes (pallor)

• other symptoms related to anemia

  • lethargy, weakness, tachypnea

  • ± icterus (uncommon) due to RBC breakdown

• decreased appetite, weight loss

• dehydration

• ± splenomegaly

• ± fever

mycoplasma haemofelis diagnostics

• CBC → regenerative anemia

• observe organisms

  • peripheral blood smear (part of CBC)

  • epicellular tiny rods, cocci, or delicate rings seen in acute phase of infection

• PCR = diagnostic method of choice

mycoplasma haemofelis treatment

• antimicrobial treatment → tetracyclines (first choice)

  • may not eliminate organisms → chronic carriers

• if severe anemia: blood transfusion

mycoplasma haemofelis prevention

• keep cats indoors (prevents cat fights with unknown cats)

• good flea control

• screen blood donor cats

is mycoplasma haemofelis contagious? is it zoonotic?

• to other cats → possible via fighting; from queen to kittens

• to people → unlikely; may be possible if immunosuppressed

bartonella gram stain/morphology

small gram-negative rods

bartonella hosts

cats, dogs, humans

what cells does bartonella infect?

infects RBCs (intracellular) and endothelial cells

• stimulates endothelial cell proliferation

bartonellosis clinical signs in animals

• usually transient, subclinical

  • cats: usually mild signs — transient fever, lymphadenitis (rare endocarditis)

  • dogs: fever, lameness, lymphadenitis, endocarditis

how is bartonella transmitted in animals?

• vector: cat fleas (ctenocephalides felis)

• zoonotic

what disease does bartonella cause in humans? how is it transmitted?

• cat scratch fever/disease

• transmission: cat scratch

cat scratch fever clinical signs

• flu-like symptoms

  • fever, chills, malaise, headaches

  • usually self-limiting

• immune-compromised people, children

  • lymphadenitis

  • endocarditis

  • bacillary angiomatosis

    • vascular proliferation in the skin → purplish nodules

  • blood-filled cystic tumors