Cardiovascular Parasites Flashcards

1
Q

Provide the taxonomy for Dirofilarial species

A

Sub class: Secernentea

Super family: Filarioidea

Family: Onchocercidae

Genus: Dirofilaria

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2
Q

List different species of Dirofilaria , along with animals do they infect and where the primary lesion site located

A

D. immitis Dogs/cats Cardiac/Pulmonary

D. repens Dogs/cats Ocular disease

D. tenius Raccoon Sub cutaneous

D. ursi Bear Sub cutaneous

D. subdermata Porcupine Sub cutaneous

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3
Q

Describe the life cycle of D. Immitis

A

Adults reach maturity and sexually reproduce in the pulmonary arteries and right ventricle

Female worms release larvae into circulation

True intermediate hosts Mosquitos ingest L1 when taking a blood meal. L1 mature into L3 whilst tin the vector

During a blood meal the L3 are injected into the bite wound by the mosquito

L3 will moult to L4 which will remain in subcutaneous tissue for a period of time

Once matured to L5 they migrate into the pulmonary arteries. Can be prepatent for 6-7months

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4
Q

Outline the factors which affect the spread of D. Immitis

A
  • Maturation of microfilariae to infective L3 requires 2 weeks >27degreesC and the temperature should not be below 14degreesC
  • Mosquito breeding on water (juvenile stages are aquatic)
  • The presence of susceptible hosts (e.g., canids) ~40 million domestic dogs in the USA and 13 million in the UK
  • Mosquito species which support the microfilariae (more than 50 known and many are in UK
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5
Q

What are the common diseases that can occur following an infection of D. Immitis?

A

Narrowing of pulmonary artery
Lead to rhs heart failure
Exercise intolerance

Hydrothorax

Hydroperitoneum

Chronic cough

Dyspnoea

Haemoptysis (cough up blood)

Eosinophilia in lung

Oedema in lung parenchyma

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6
Q

How does D. Immitis lead to pulmonary hypertension

A

Hypertension is NOT caused by blockage but by hypertrophy (inflammation)of the medial layer of the pulmonary artery

Adult D. immitis in the pulmonary artery

Disruption of intima leads to platelet (thrombocyte) influx and production of platelet derived growth factor (PDGF)

PDGF increases proliferation of medial smooth muscle cells and fibroblasts

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7
Q

What are the key immune cells involved in D. Immitis

A

Eosinophils
Basophils
Mast Cells

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8
Q

What are the roles of eosinophils in D. immitis?

A

Important in parasitic and allergic diseases (migrate from blood into tissue)
Increased numbers (eosinophilia) occur in blood and tracheal washes during cardiorespiratory parasitism

Degranulation at parasite surface causes damage to parasite (and sometimes host tissue also)

2 types of granule:
		
		Large Specific Granule
		Major basic protein, eosinophil cationic protein, eosinophil derived 
                    neurotoxin, eosinophil peroxidase
		
		Small Granules
		 Aryl sulphate, acid phosphatase, gelatinase

Cytokines involves:
	 IL-3, IL-5 (Eosinophil growth factors)
	 IL-1, IL-6, IL-8, TNF-alpha
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9
Q

What are the roles of basophils in D. immitis?

A

Basophils degranulate at surface of blood borne parasites (microfilariae).

Although factors, such as histamine are produced, the granules also contain the same substances as eosinophil large specific granules

Histamine is an important vasodilator which increases the number of immune cells in tissue

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10
Q

What are the roles of mast cells in D. immitis?

A

Closely related to basophils (tissue version)

Activated & produce amines such as histamine

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11
Q

If neutrophils respond to bacteria and fungal infection why do we see them in the walls of the pulmonary artery during heartworm disease of dogs?

A

D. immitis carries Wolbachia (a Rickettsial bacterium) which plays a role in neutrophil-induced inflammation seen in heartworm infection

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12
Q

Outline Caval Syndrome

A

It is a clinical Emergancy

Large worm burden in the right atrium and posterior vena cava

Increased venous pressure damages liver parenchyma

Increases cholesterol content of erythrocyte membranes leading to more fragility and haemolysis

Severe (regenerative) anaemia (many immature/nucleated red cells may be seen in blood as
erythrocytes are replaced (may see immature RBC in circulation)

Erythrocyte haemolysis leads to haemoglobinaemia (free haemoglobin in blood) and bilirubinaemia (bilirubin in blood) and haemoglobinuria (blood in urine) and jaundice

Dog may suddenly collapse/die

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13
Q

Outline the diagnostic tests used for D. Immitis

A

Complete blood count (CBC) (same as haematology) - may see increase eosinophils and basophils (may not see this and is non specific finding)

Knotts test/Milipore filter (acidic phosphatase staining or methylene blue) to enrich the microfilariae (MFs). Test to vie larvae within the blood

Thoracic radiographs

Electrocardiogram (ECG)/Echocardiogram (more helpful then electrocardiogram). May see worms in righ ventricle

Arteriogram

Indirect fluorescent antibody (IFA)

ELISA (Adult antigen) looking for antigens form female worms

Tracheal wash

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14
Q

Discuss the limitations of diagnostic tests

A

No test is the definitive

CBC.
Some other diseases will give similar results

Smears and concentration tests.
Microfilariae may not be seen if few are present. In both tests, occult infections are
not detected

Echocardiogram.
May be difficult to interpret

Radiology.
Signs may be similar to other diseases

ELISA.
Only adult female antigens detected. False negatives occur if immature females p
resent or male only infection (or problem with the kit)

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15
Q

What are the treatments available for D immitis

A

Adult worms:
Melarsomine dihydrochloride (Immiticide®)

Microfilariae:
Ivermectin- contraindicated in CNS pathology
Milbemycin

Both can be used as preventatives for prophylaxis
(Ivermectin = Heartguard®)
(Milbemycin = Interceptor®)

Surgical Removal

 In very heavy infections adulticide treatment may lead to severe pathology (dead 
 worms may cause thromboembolism)

 During caval syndrome worms should be removed very quickly

Prognosis and complications from treatment as well as cost should be communicated 
to and discussed with clients before it is undertaken.
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16
Q

What is the significance of Dipetalonema reconditum in relation to D. Immitis

A

Common in USA, and adults are sub-cutaneous and not thought to be of clinical significance

We may need to distinguish D. reconditum microfilariae from D. immitis microfilariae in heartworm endemic regions

Its significance is probably in false positive D. immitis results. But, acid phosphatase test can determine the species.

17
Q

Compare Canine D. Immitis and Feline D. Immitis

A

Cats are much more resistant but are still receptible

Adult worms do not live as long in cats (2-3 years) as in dogs (5-7 years)

Increased immune response with fewer adult worms

Primarily resides in lungs in cats whereas is in the lungs and heart of dogs

Overall effect is that cats are not as good of reservoir of D. Immitis and very few worms can cause significant disease

18
Q

What complications arise when diagnosing feline D. immitis

A

Usually amicrofilaraemic (no microfilariae in blood) (<20% and only for about 1 month) therefore blood smears may give false negative (Occult infections)

Diagnosis may be improved by analysing blood samples acquired in the evening where the parasites are more active (called nocturnal periodicity)

Clinically infected cat may have very low worm burdens. Therefore, ELISA analysis to detect antigen may give false negative

Single sex infections occur more in cats (No microfilariae produced)

19
Q

How has the ELISA test been adapted to better suit diagnosis of feline D. immitis

A

In cats very few worms may cause significant pathology

ELISA which detects antigen (used in dogs) may not be sensitive enough

The ELISA developed for use in cats therefore measures antibody to parasite (rather than parasite antigen)

20
Q

Outline the limitations of the antibody based ELISA test

A

Positive antibody results may not tell you current status since blood antibody can be present in cats which have previously been infected

Although antibody titre can be raised in on-going infection it is difficult to correlate antibody titre with worm burden or current/previous infection

It is therefore a less appropriate screening test and should be interpreted in relation to clinical signs and other diagnostic findings

21
Q

If D. immitis infection in cats predominantly presents as lung disease. What other diagnostic tests may we need to do?

A

BAL is a valuable diagnostic tool for evaluation of cats with lower respiratory tract disease.

22
Q

What factors may increase the possibility of becoming an important UK pathogen in the future?

A

Introduction of exotic infection with imported rescue pets or with pet returning from endemic areas abroad

Climate change/global warming and increase in vector population and activity season (i.e., adult mosquito can live long enough in warmer climates for heartworm to complete its life cycle