Lesson 41 - Vector Borne diseases of Equine

What is the difference between rickettsieae and anaplasmataceae intracellular location?

1. rickettsiaceae replicates in cytoplasm

2. anaplasmataceae replicates inside membrane-bound vacuoles (morulae)

What is the difference between rickettsieae and anaplasmataceae target host cells?

1. rickettsiaceae infects endothelial cells

2. anaplasmataceae infects leukocytes such as granulocytes or monocytes

What is the difference between rickettsieae and anaplasmataceae pathology and clinical presentation?

1. rickettsiaceae causes fever, rash, severe vasculitis

2. anaplasmataceae does not typically cause vasculitis

What rickettsia disease is in horses?

Rickettsia raoulti

What is the vector for Rickettsia in horses?

Dermacentor

What are the clinical signs of Rickettsia in horses?

1. often asymptomatic

2. fever, lethargy, anorexia

3. muscle issues

What can horses act as for Rickettsia raoulti?

reservoir for ticks

What is the concern with Rickettsia raoulti?

zoonosis

What is the causative agent for potomac fever?

1. neorickettsia risticii bacteria

2. aquatic snails

3. aquatic insects

How is potomac fever transmitted?

horses ingest infected insects while grazing especially in the summer/fall

Is potomac fever contagious?

no

What cells does neorickettsia risticii infect?

1. macrophages

2. monocytes

3. intestinal epithelial cells

What is the inflammatory response to N. risticii?

severe inflammation of the intestinal wall particularly in the small intestine, colon, and cecum

What is a sequela to N. risticii causing intestinal lining damage?

endotoxins enter the bloodstream causing symptoms fever, leukopenia, and shock

What are the clinical signs of potomac fever?

1. fever, lethargy, depression

2. anorexia

3. colic

4. profuse watery diarrhea

5. laminitis

6. abortion in pregnant mares

What is the diagnostic test used for potomac fever?

PCR of blood or feces

How is potomac fever treated?

1. IV oxytetracycline

2. IV fluids

3. NSAIDs

4. digital cryotherapy to prevent laminitis

How do we prevent potomac fever?

1. remove from water sources

2. isolate cases while ruling out other diseases

3. vaccination is available but not 100% effective

What is the prognosis for potomac fever?

1. good with early diagnosis and aggressive treatment especially if laminitis is prevented

2. guarded if severe laminitis develops

What is anaplasmosis called in equine?

equine granulocytic ehrlichiosis

What is the anaplasma agent in equine?

Anaplasma phagocytophilum

What is the vector for A. phagocytophilum?

Ixodes tick bite

When does bacteremia develop after infection with A. phagocytophilum?

5-7 days; bacteria is in the skin until then

What is the immune response to A. phagocytophilum?

TH1 immune response with cytokine related inflammation in small vessels causing vasculitis

What are the clinical signs of A. phagocytophilum?

1. adult horses

2. fever accompanies bacteremia lasting several days

3. stiffness

4. limb edema

5. anorexia

6. icterus

7. petechiae

What are other less common syndromes associated with equine anaplasmosis?

1. myopathy

2. cavitary effusion

3. DIC/acute death

4. myelitis/encephalitis

5. hepatitis

6. pulmonary distress

What are the pulmonary lesions seen with A. phagocytophilum?

1. mild perivascular lymphohistiocytic infiltrates

2. patchy, alveolar wall edema

3. infiltrates mostly macrophages and lymphocytes

What are the liver changes seen with A. phagocytophilum?

1. increased liver enzymes with GGT increased

2. nuclear cell infiltrates to slight lobular hepatits

3. intra-sinusoidal aggregates of macrophages

4. focal apoptotic cells

What is the clinical pathology with A. phagocytophilum?

1. severe leukopenia during early clinical signs

2. thrombocytopenia

3. mild anemia

4. lymphoid depletion in spleen but little effect on bone marrow

5. bands don't have inclusions

6. neutropenia variable

What are the diagnostics used for A. phagocytophilum?

1. clinical signs and tick exposure

2. PCR on whole blood during febrile stage

3. Giamsa stain of blood

4. IFA on serum after febrile stage

5. Snap 4Dx has 50% sensitivity

What are the cbc key changes with A. phagocytophilum?

1. thrombocytopenia

2. neutropenia

How long will horses be PCR positive after treatment of A. phagocytophilum?

1-2 days

How long will horses be IFA negative after the febrile stage of A phagocytophilum?

up to 3 weeks or remain negative

What are the treatment options for A. phagocytophilum?

1. oxytetracycline

2. doxycycline/minocycline

3. natural immunity lasts 1 year

What drugs do we not want to use for A. phagocytophilum?

1. penicillin

2. ampicillin

3. chloramphenicol

4. streptomycin

What are the prevention measures for A. phagocytophilum?

1. environmental tick control

2. physical exam and regular inspection

3. insecticides

What insecticides can be used for tick control of A. phagocytophilum?

1. coumaphos spray or powder

2. pyrethrins

3. synthetic pyrethroids

4. zeta-cypermethrin dusting powders most commonly used

What does Borrelia burgdorferi infect?

1. leukocytes

2. synovial lining cells

What leads to the persistent clinical signs seen with B. burgdorferi?

persistence of bacteria within both synovial structures and tendons

What serology result may occur in a clinically healthy horse living in a lyme endemic area?

positive antibody levels

What are the main syndromes that occur due to B. burgdorferi?

1. neuroborreliosis

2. uveitis

3. shifting leg lameness

4. muscle wasting

5. herpesthesia

6. nuchal bursitis

7. pseudolymphoma

What are characteristics of lyme uveitis?

1. rapidly progressive bilaterally

2. organism found predominantly in vitreous fluid

3. may precede onset of CNS signs

What is pseudolymphoma?

atypical cutaneous nodular lymphoid hyperplasia

What clinical signs are reported with neuroborreliosis?

1. muscle atrophy

2. cranial nerve deficits

3. ataxia and paresis

4. changes in behavior like narcolepsy

5. fasciculations

6. hyperesthesia

7. neck and back stiffness with pain

8. concurrent uveitis

What does positive serology with lyme disease mean?

recent exposure not necessarily clinical disease

What are the diagnostics used for lyme?

1. known exposure to possible borrelia infected ticks

2. clinical signs

3. cytology, histopathology

4. response to treatment

What is used for cytology or histopathology for borrelia?

1. CSF but usually negative

2. ovular fluid typically positive on cytology and PCR

3. joint fluid

What is the most common histopathologic lesion of lyme disease in horses?

lymphohistiocytic and plasmacytic infiltrate

What lesion can be seen with neuroborreliosis?

gross thickening of the dura

When is serologic testing recommended for horses?

horses with compelling clinical signs

When is treatment for borrelia indicated?

seropositive horses with clinical signs consistent with lyme disease

What are the drugs used to treat lyme disease?

1. penicillin

2. ceftiofur

3. tetracyclines

What drugs are not recommended for lyme disease?

1. ceftriaxone

2. metronidazole

3. enrofloxacin

What gender tick is most responsible for transmitting lyme disease?

adult females in early spring or in fall

Is there a vaccine for lyme disease in horses?

no FDA-approved vaccine but canine lyme vaccine used off-label for partial short-lived protection in endemic areas

What is recommended prior to vaccinating horses for lyme?

pre-testing

What pathogen causes piroplasmosis?

1. babesia cabelli

2. theileria equi

What is the disease status of piroplasmosis?

reportable disease

What type of organism is babesia and theileria?

protozoa

What cells are infected with equine piroplasmosis?

erythrocytes

What are the different presentations seen with piroplasmosis?

range from subclinical to fatal

When do clinical signs appear after infection with piroplasmosis?

5-28 days

What are the clinical signs seen with piroplasmosis?

1. severe anemia

2. high fever

3. lethargy

4. icterus

5. anorexia

What are the acute clinical signs of piroplasmosis?

1. labored breathing

2. dark urine

3. colic

What are the clinical signs seen with chronic piroplasmosis?

1. weight loss

2. poor performance

What are the diagnostic tests used for piroplasmosis?

1. competitive ELISA and IFA for international movement

2. blood smear, PCR, paired serology for acute cases

3. cELISA or CFT for chronic/subclinical cases

What is the treatment plan for piroplasmosis?

1. imidocarb dipropionate IM

2. nutritional support

3. vitamin/mineral supplementation

What animal do we not give imidocarb dipropionate to?

donkeys

What is the medication protocol for B. caballi?

2 injections of imidocarb dipropionate 24 hours apart

What is the medication protocol for T. equi?

4 injections of imidocarb dipropionate at 72 hour intervals

What are the side-effects to imidocarb?

1. colic

2. diarrhea

3. restlessness

4. pre-treat with antispasmodics