L83b: parasitic vascular disease

what parasite causes heartworm?

dirofilaria immitis

what type of parasite is heartworm?

filarial nematode

who are the definitive hosts of heartworm?

dogs and cats

who are occasional hosts for heartworm?

1. ferrets

2. humans

where do adult heartworms live?

• pulmonary arteries

• severe infections = right heart

what is the lifespan of heartworm in the dog?

5-7 years

what is the lifespan of heartworm in the cat?

2-3 years

what is the lifecycle for heartworm?

indirect with mosquito as intermediate host

what stage are heartworm microfilariae?

L1

where do heartworm microfilariae circulate?

in blood of an infected host

what stage does L1 develop into in the mosquito for heartworm disease?

infective L3 stage

how long does it take for L1 to develop into L3 in the mosquito for heartworm disease?

10-14 days

what is the worm burden in dogs for heartworm disease?

variable (low to high)

what is the worm burden in cats for heartworm disease?

very low (less than 5 worms)

what are the clinical signs of heartworm disease in dogs?

1. cough

2. exercise intolerance

3. weight loss

4. hemoptysis

5. ascites

6. sudden collapse

what are the clinical signs of heartworm disease in cats?

1. coughing

2. dyspnea

3. vomiting (common and may be only sign)

what causes an immune response to heartworm in dogs?

adult worms in pulmonary arteries

what causes an immune response to heartworm in cats?

immature worms in lungs

what is the treatment for heartworm in cats?

• no adulticide approved

• supportive care and prevention

what is wolbachia pipientis?

an endosymiotic bacterium that lives within dirofilaria

what treatment do we use to target wolbachia?

doxycycline

why do we want to kill the wolbachia before we kill the adult heart worms?

decreases microfilarial viability and limits inflammation when adult worms die

what causes caval syndrome in dogs?

large worm burden in right heart and vena cava

which valve is obstructed with caval syndrome?

tricuspid valve

what are the clinical signs for a mild (class 1) case of heartworm in dogs?

no clinical signs or cough

what are the clinical signs for a moderate (class 2) case of heartworm in dogs?

1. cough

2. exercise intolerance

3. abnormal lung sounds

what are the clinical signs for a severe (class 3) case of heartworm in dogs?

1. cough

2. exercise intolerance

3. abnormal heart or lung sounds

4. hepatomegaly

5. ascites

6. sudden death

what are the clinical signs for a cava syndrome (class 4) case of heartworm in dogs?

1. hemoglobinuria

2. anemia

3. low-output heart failure

What clinical presentation is most characteristic of feline heartworm disease compared with canine infection?

acute respiratory distress with possible sudden death despite low worm burden

what occurs with stage 1 heartworm disease in cats?

immature lungs reach lungs → acute inflammation

what occurs with stage 2 heartworm disease in cats?

death of worms → severe inflammation (can be lethal)

what occurs with stage 3 heartworm disease in cats?

chronic lung remodeling and respiratory disease (may cause sudden death even with low worm burden)

A 4-year-old Labrador retriever presents for annual examination. The

owner reports no clinical signs. A heartworm antigen test is positive.

Which stage of the parasite is most likely being detected by this test?

adult female worms in pulmonary arteries

what are diagnostic methods for heartworm disease?

1. antigen testing (ELISA)

2. microfilaria tests

3. imaging

4. CBC and chemistry

what does the ELISA test detect for heartworm?

adult female uterine antigen

why may we get a false-negative with an ELISA test for heartworm?

1. low burden

2. all-males

what are some tests for microfilaria?

1. modified knott’s

2. wet mount

what will you find on CBC and chemistry for heartworm?

1. eosinophilia

2. mild anemia

3. may have elevated liver enzymes

how is acathocheilonema reconditum different that diofilaria imminitis?

1. smaller

2. curved

3. progressive motility

4. blunt head and hooked tail

A 4-month-old intact male Labrador Retriever is presented for a routine examination. The puppy is clinically normal. The breeder reports that heartworm prevention was started recently but cannot provide complete medical records. Diagnostic testing yields:

Heartworm antigen: negative

Modified Knott’s test: microfilariae morphologically consistent with Dirofilaria immitis

Which of the following is the most likely explanation for these findings?

The puppy acquired D. immitis shortly after birth, and microfilariae became detectable before

maturation of antigen-producing females

what is used to prevent heartworm infection?

macrocytic lactones

how do macrocytic lactones work against heartworm?

kills L3/L4 larvae acquired in the previous month

what is essential through out heartworm treatment?

exercise restriction

what is the protocol in dogs for heartworm treatment?

three-dose melarsomine protocol

what is done on day 0 of the melarsomine protocol?

1. diagnosis confirmed

2. start heartworm preventative

3. start doxycycline

4. start prednisone (if symptomatic)

5. begin exercise restriction

what is done on day 60 of the melarsomine protocol?

1. first melarsomine injection

2. start prednisone dose

what is done on day 90 and 91 of the melarsomine protocol?

1. second and third melarsomine injections

2. prednisone

what are the benefits of giving doxycycline before heartworm adulticide therapy?

1. disrupts heart worm transmission

2. reduces pathology associated with dead worm

what does prednisone do in the treatment for heartworm?

reduces inflammation caused by dying heartworms

what are the benefits of giving prednisone in heartworm treatment?

1. decreases pneumonitis

2. reduces coughing and respiratory signs

3. lowers risk of thromboembolic complications

why is melarsomine included in heartworm therapy?

kills adult heartworms residing in the pulmonary arteries and heart (DOGS ONLY)

what is the longest strongyle of equine?

strongulus vulgaris

what is the lifecycle of strongulus vulgaris?

• direct

• egg passed in feces → L1-L3 develop on pasture → horse ingest infective L3 larvae

where does L3 of strongulus vulgaris go once in the horse?

penetrates the intestinal wall to migrate to cranial mesenteric artery

where do adult strongulus vulgaris go in the horse?

cecum and colon

what are the clinical signs of strongulus vulgaris in a horse?

1. colic

2. ileus

3. possible intestinal rupture

4. fever

5. depression

6. anorexia

what is the treatment for adult strongulus vulgaris in horses?

antiheminthics

what is the treatment for strongulus vulgaris larvae in horses?

ivermectin or moxidectin

what can be used in the diagnostic of strongulus vulgaris in horses?

1. fecal egg count

2. serology for antibodies

3. ultrasound

what is the issue with fecal egg count for strongulus vulgaris?

cannot differentiate strongulus vulgaris from other strongyles

a dog with severe heartworm disease develops intravascular hemolysis and dark reddish-brown urine. Echocardiography demonstrates worms obstructing the tricuspid valve. which explanation best accounts for the hemoglobinuria?

mechanical disruption of erythrocytes associated with intracardiac worm obstruction

A horse with inadequately controlled strongyle infection is found to have thickening and thrombosis of the cranial mesenteric artery. Which pathological mechanism best explains this lesion?

verminous arteritis caused by migrating larvae

An 8 year old horse develops acute severe colic, ileus, and signs of intestinal ischemia. A history of poorly controlled strongyle infection raises suspicion for strongylus vulgaris. Which event most directly produces intestinal ischemic injury?

thromboembolism originating from damaged mesenteric arteries

A horse grazed on contaminated pasture approximately 2 months ago. The horse now has abdominal discomfort, but routine fecal examination is negative for strongyle eggs. Strongylus vulgaris infection remains suspected. Which explanation best accounts for these findings?

the parasite has a prepatent period of approximately 6-7 months, so migrating larvae may cause disease before egg production

A horse develops verminous arteritis due to strongylus vulgaris infection. Several weeks later, the horse exhibits severe abdominal pain and decreased intestinal motility. Which sequence best connects the parasitic infection to clinical signs?

arterial larval migration → endarteritis and thrombosis → impaired intestinal perfusion → ischemia and ileus