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Flashcards in Canine heartworm Deck (34):
1

Pathophysiology

  • Dirofilaria immitis
    • Transmitted >60 mosquito species
    • Worldwide, prevalent in Eastern and Southern US
    • Dogs may have up to 250 worms (ave. ~15)
  • Adult worms destroy endothelium of small pulmonary arteries, esp. caudal lung lobes
    • --> inc. permeability--edema, coughing, dyspnea
  • Myointimal proliferation--> thickening + narrowing--> lose normal tapering/bronchial pattern
  • Pulmonary hypertension--> cor pulmonale w/ R ventricular eccentric hypertrophy
  • Worms release substances
    • Vasoconstriction, bronchioconstriction
    • Inflammation, fibrosis
  • Wolbachia
  • Glomerulonephritis, proteinuria

2

Pathiophysiology: dead worms

  • Proliferation smooth muscle
  • Granulomas in vessel walls
  • Thrombus formation
  • Lung consolidation
  • Acute CHF

3

Signalment

  • Signs seen in dogs >6mo
  • Males, middle aged
  • Outdoor
  • Large breed
  • Endemic areas

4

History

  • No macrocyclic lactone use
  • Most asymptomatic--(+) at routine tests
  • Wt. loss
  • Anorexia
  • Chronic non-productive cough
  • Dyspnea
  • Exercise intolerance
  • Hemoptysis (rare/severe dz)
  • Abdominal enlargement--RCHF/caval syndrome

5

Physical exam

  • Depends on severity
  • Split second heart sound
  • Tracheal sensitivity
  • Inc. RR/depth
  • Harsh lung sounds, crackles
  • Wt. loss
  • Right heart failiure signs
    • Ascites
    • Hepatosplenomegaly

6

Diagnostics

Laboratory: definitive diagnosis, specific tests

  • Definitive diagnosis--ID D immitis microfilaria in blood
    • Appear 6-7mo post-infection
  • Conc. tests: 10-67% false (-)
    • Reproductively senile worms
    • Prepatent infections
    • Unisex infections
    • Immune responses kill microfilaria (eos. pneumonia)
    • Sporadic use of microcyclic lactones
  • Antibody tests: false (+)
  • Antigen tests: glycoprotein (females), specific + sensitive (>80s%)

7

Diagnostics

Laboratory: hematology, chemistries

  • Hematology
    • Thrombocytopenia common
    • Inc. eos, basophils (maybe)
    • Mild non-regenerative anemia--chronic inflammation
  • Chemistry
    • Maybe hyperglobulinemia (or hypoalbuminemia)
    • Elevated liver enz

8

Diagnostics

Imaging

  • Changes seen early useful for characterizing severity
  • VD for R heart and main pulmonary artery
  • DV for caudal lobar arteries
  • R ventricular enlargement
  • Prominent main pulmonary artery (1 o'clock, giving an inverted D)
  • Enlarged lobar arteries (esp. R caudal pulmonary artery)
  • Poss. broncho-alveolar patterns

9

Diagnostics

ECG

R ventricular enlargement may be seen in moderate to severe cases

10

Diagnosis summary

  • Ag assay + microfilaria
  • Rads = lung severity
  • Ultrasound = heart severity
  • General health profile

11

Treatment

Goals

  • Begin animal on prophylaxis--to prevent further infections
  • Manage signs of mod/severe lung disease and heart failure
  • Kill microfilaria
  • Adulticide therapy

12

Treatment: prophylaxis

General

 

  • Animal placed on preventative and adulticide trtmt delayed 2-3 months (esp. during peak/summer months
  • + doxycycline for ~1mo should kill most Wolbachia
  • Doxy and ivermectin prevent embryo formation in females and stunt growth
    • Poss. less lung pathology
    • Smaller mass of worms
  • Indicated for all dogs at risk starting 6-8wks old
  • Lack of efficacy reports (mult. reasons)
  • DEC (filaribits)--L3-L4 moult; microfilaria
  • Ivermectin and collies
    • L3 and L4--1m reachback/safety net
    • Microfilaria--6-8mo
    • Adulticidal--2.5yrs (resistance)

13

Treatment: prophylaxix

Specific drugs

  •  Diethylcarbazamine (DEC, filaribits)
    • Safe/effective when given daily
    • L3-L4 molt stage
    • Microfilaria (severe rxns if dog not amicrofilaremic)
  • Ivermectin (Heartgard)
    • L3 & L4 (1m); reachback/safety net
    • Microfilaria--6-8mo
    • Adulticidal--2.5yrs (resistance)
  • Milbemycin (Interceptor, Sentinel)
    • L3 & L4 (1m)
    • Good microfilaricide
    • Not adulticidal
  • Selamectin (Revolution)
    • L3 & L4 (1m)
    • Slow microfilaricide
    • Slow adulticide
  • Moxidectin (Advantage multi, Proheart)
    • L3 & L4 (1m)
    • Registered microfilaricide
    • Slow adulticide

14

Treatment

Drugs--killing microfilaria

  • Poor--selamectin
  • Best--moxidectin***, milbemycin (10% signs)
    • Before or after adulticide?
  • 2nd best--ivermectin
    • 5mcg/kg for 6-8 mo
    • Resistance potential
  • Ivermectin + doxy more effective

15

Treatment: adulticide therapy

Goal

  • Elimination of all adult heartworms
  • HW antigen test should be negative by 16wks post-adulticide treatment

16

Treatment: adulticide therapy

Melarsomine

  • Immiticide
  • Now the drug of choice for heartworm trtmt
  • Kills immature (4m, L5) and mature adult stages
  • Rarely causes hepato- or nephrotoxicity (at correct dosing)
  • Dogs asymptomatic (Class 1) or w/ mild signs (class 2): 2 im injections at 24hrs
  • Dogs w/ severe disease (class 3) or w/ caval syndrome (class 4): 1 im injection then 2 more ~a month later
  • Pred/NSAID?

17

Treatment

Post-adulticide: problems?

  • Cage rest (at least 4-6 wks after treatment)
  • Worms die at 3-21 days; most severe comlications arise 2-3 wks after treatment 
  • Pulmonary thromboembolism
  • Dyspnea (>40-50 bpm), coughing, hemoptysis, fever
  • Dyspnea in a dog post adulticide treatment is an EMERGENCY
    • Strict cage rest, oxygen therapy, prednisolone, bronchodilators
  • Fluids--CAUTION: may exacerbate pulmonary edema and R heart failure
  • DIC (severe pulmonary signs, bleeding), thrombocytopenia (<100,000)

18

Treatment

Post-adulticide--treatment

  • Oxygen, pred, bronchodilators, furosemide, fluids (w/ care)
  • Aspirin--NOT recommended

19

Treatment

Ivermectin

  • Used when arsenicals/cagerest/melarsomine treatment is unavailable 
  • Slow adulticide activity (kills occur over a few years) w/ monthly administration

20

Treatment

Surgical removal

  • Flexible alligator forces + fluoroscopic guidance
  • Improves survival in animals with high risk of pulmonary thromboembolism

21

Prognosis

  • Asymptomatic/mild disease--good (<5% mortality)
  • Marked disease--guarded prognosis (up to 20% mortality)
  • Lung changes may persist w/ chronic cough
  • Some cases so severe only symptomatic treatment

22

Post-caval syndrome

Pathophysiology

  • Aka 'vena-caval syndrome)
  • Heavy burdens of worms not only in pulmonary arteries but also in R atrium and even caudal vena cava
  • --> incomplete closure of tricuspid valve and inc. resistance to flow in posterior vena cava
  • --> hepatic congestion--> ascites
  • Intravascular hemolysis--> anemia, hemoglobinemia, hemoglobinuria, jaundice, DIC

23

Post-caval syndrome

Clinical signs

Diagnosis

  • Dogs usually present after acute collapse and are in shock
  • Echodardiology--shows worms in R atrium and posterior vena cava, and shows tricuspid valve insufficiency

24

Post-caval syndrome

Treatment

  • Jugular venotomy and removal of worms w/ forceps/retrieval basket immediately
  • Don't crush worms--can result in acute resp. distress or acute heart failure
  • Remaining worms removed via chemotherapy

25

Feline heartworms

General--incidence?

  • Cats only incidental hosts--> 
    • <10% L3 reach adulthood
    • Prepatent infections are longer than in dogs (8mo)
    • Fewer adult worms develop (2-4) and have shorter lifespans
    • Occult infections common 
    • Microfilaria are few and short-lived
  • Though only 5-10% that of dogs, when clinical heartworm disease occurs in cats it is often serious and life-threatening

26

Feline heartworm

Pathophysiology

  • Clinical signs arise at 2 stages of infections
    • L5 arrive in lungs
      • Acute vascular and parenchymal inflammatory response (eosinophilic pneumonitis/HARD--heartworm-assoc. resp. disease)
      • Commonly confused w/ feline asthma
      • The few adult worms that dev. cause only local arteritis--> most established infections are asypmtomatic
    • Adult worms die (even only 1 worm)
      • Thromboembolism and host rxns in cat are very severe and can result in fatal lung changes
  • Ectopic infections more common than in dogs--may result in seizures, head tilt, blindness, etc. 

27

Feline heartworm

Signalment

History

  • Signalment: 3-6yr, male, indoor
  • History
    • Resp. signs (acute or chronic cough, dyspnea)
    • Vomiting
    • Asymptomatic
    • Sudden death
    • Weakness/syncope
    • Other signs from aberrant migration (esp. CNS)
    • Most cats present w/ chronic history of anorexia, wt. loss, exercise intolerance, cough and/or vomiting
    • Almost 50% present w/ acute case of dyspnea (L5 in lugs or when adult worms die)

28

Feline heartworm

Usual findings on PE

  • Usually normal
  • Poss. heart lung sounds (occasionally)
  • Ascites, heart murmurs and gallop rhythms are uncommon
  • Sometimes might be murmur when heartworms interfere w/ tricuspid valve fx

29

Feline heartworm

Special test findings

  • No single test--composite of signs (unlike in dogs)
  • Lab
    • Mild non-regenerative anemia
    • Eosinophilia often inconsistent and intermittent
    • Hyperglobulinemia poss.
  • Imaging
    • Abnormalities seen in 60-70%
    • Alveolar densities (respond to pred)
    • Enlarged caudal arteries (esp. on R)
    • Hyperinflation--feline asthma
    • Tortuosity/pruning rare, heart/main pulm artery signs rare
  • Angiography--enlargement, tortuosity, pruning of pulm. arteries may be seen
  • Echo--worms seen in 50%
  • EKG--maybe R axis deviation, VPDs

30

Feline heartworm

Tests

  • Microfilaria tests--90% false (-); 2-4 worms
    • All male
    • Immature/senile females
    • No males
  • Antibody tests--false (+)
    • L3, L4, L5 exposure
    • Prophylactics
    • Cleared adult infections--6mo; false (-)
    • Dif. antibodies
    • Lower titers in older infections
  • Antigen tests--specific (+ result CONFIRMS diagnosis of HW)
    • ​False (-)
      • Too few females
      • All male
      • Immature/senile females

31

Feline heartworms

Treatment--adulticide therapy?

  • Adulticide treatment no longer recommended
    • Melarsamine not very effective + severe rxns and toxicities
    • Survival w/ prophylaxis and symptomatic treatment = survival w/ adulticide therapy

32

Feline heartworm

Treatment--"accepted" guidelines

  • Asymptomatic, ag/ab positive, normal rads
    • No treatment; prophylaxis
  • Symptomatic, ag/ab positive, abnormal rads
    • No adulticide--just supportive pred as needed, no aspirin
    • Crisis--oxygen, dex/pred IV, furosemide, ACE, digoxin
  • Physical removal poss--jugular venotomy, thoracotomy, and atriotomy/pulmonary arteriotomy (var. results)
  • Ivermectin at prophylactic dose (1 study)

33

Feline heartworm

Prevention

  • RECOMMENDED, esp. in endemic areas
  • Heartgard, milbemax, revolution, advantage multi
  • Ab tests might become + 
  • Questionable if screening tests necessary before prophylaxis

34

Feline heartworm

Prognosis

DDx

  • Prognosis--guarded
    • Sudden death can occur w/ only 1 worm
    • Good if placed on preventatives and survives past 2 years
  • DDx
    • Coughing--parasitic lung disease--Aleurostrongylus
    • Paragonimus--feline asthma, cardiomyopathy
    • Dyspnea--pleural effusion, FIP, anemia, lymphosarcoma