Canine heartworm Flashcards
1
Q
Pathophysiology
A
-
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
Q
Pathiophysiology: dead worms
A
- Proliferation smooth muscle
- Granulomas in vessel walls
- Thrombus formation
- Lung consolidation
- Acute CHF
3
Q
Signalment
A
- Signs seen in dogs >6mo
- Males, middle aged
- Outdoor
- Large breed
- Endemic areas
4
Q
History
A
- 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
Q
Physical exam
A
- 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
Q
Diagnostics
Laboratory: definitive diagnosis, specific tests
A
-
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
Q
Diagnostics
Laboratory: hematology, chemistries
A
- Hematology
- Thrombocytopenia common
- Inc. eos, basophils (maybe)
- Mild non-regenerative anemia–chronic inflammation
- Chemistry
- Maybe hyperglobulinemia (or hypoalbuminemia)
- Elevated liver enz
8
Q
Diagnostics
Imaging
A
- 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
Q
Diagnostics
ECG
A
R ventricular enlargement may be seen in moderate to severe cases
10
Q
Diagnosis summary
A
- Ag assay + microfilaria
- Rads = lung severity
- Ultrasound = heart severity
- General health profile
11
Q
Treatment
Goals
A
- Begin animal on prophylaxis–to prevent further infections
- Manage signs of mod/severe lung disease and heart failure
- Kill microfilaria
- Adulticide therapy
12
Q
Treatment: prophylaxis
General
A
- 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
Q
Treatment: prophylaxix
Specific drugs
A
- 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
Q
Treatment
Drugs–killing microfilaria
A
- 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
Q
Treatment: adulticide therapy
Goal
A
- Elimination of all adult heartworms
- HW antigen test should be negative by 16wks post-adulticide treatment
16
Q
Treatment: adulticide therapy
Melarsomine
A
- 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
Q
Treatment
Post-adulticide: problems?
A
- 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
Q
Treatment
Post-adulticide–treatment
A
- Oxygen, pred, bronchodilators, furosemide, fluids (w/ care)
- Aspirin–NOT recommended
19
Q
Treatment
Ivermectin
A
- Used when arsenicals/cagerest/melarsomine treatment is unavailable
- Slow adulticide activity (kills occur over a few years) w/ monthly administration
20
Q
Treatment
Surgical removal
A
- Flexible alligator forces + fluoroscopic guidance
- Improves survival in animals with high risk of pulmonary thromboembolism
21
Q
Prognosis
A
- 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
Q
Post-caval syndrome
Pathophysiology
A
- 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
Q
Post-caval syndrome
Clinical signs
Diagnosis
A
- 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
Q
Post-caval syndrome
Treatment
A
- 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
Q
Feline heartworms
General–incidence?
A
- 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
Q
Feline heartworm
Pathophysiology
A
- 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
- L5 arrive in lungs
- Ectopic infections more common than in dogs–may result in seizures, head tilt, blindness, etc.
27
Q
Feline heartworm
Signalment
History
A
- 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
Q
Feline heartworm
Usual findings on PE
A
- 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
Q
Feline heartworm
Special test findings
A
- 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
Q
Feline heartworm
Tests
A
- 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
- False (-)
31
Q
Feline heartworms
Treatment–adulticide therapy?
A
- Adulticide treatment no longer recommended
- Melarsamine not very effective + severe rxns and toxicities
- Survival w/ prophylaxis and symptomatic treatment = survival w/ adulticide therapy
32
Q
Feline heartworm
Treatment–“accepted” guidelines
A
- 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
Q
Feline heartworm
Prevention
A
- RECOMMENDED, esp. in endemic areas
- Heartgard, milbemax, revolution, advantage multi
- Ab tests might become +
- Questionable if screening tests necessary before prophylaxis
34
Q
Feline heartworm
Prognosis
DDx
A
- 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
