Cardiovascular Parasites Flashcards
Provide the taxonomy for Dirofilarial species
Sub class: Secernentea
Super family: Filarioidea
Family: Onchocercidae
Genus: Dirofilaria
List different species of Dirofilaria , along with animals do they infect and where the primary lesion site located
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
Describe the life cycle of D. Immitis
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
Outline the factors which affect the spread of D. Immitis
- 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
What are the common diseases that can occur following an infection of D. Immitis?
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
How does D. Immitis lead to pulmonary hypertension
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
What are the key immune cells involved in D. Immitis
Eosinophils
Basophils
Mast Cells
What are the roles of eosinophils in D. immitis?
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
What are the roles of basophils in D. immitis?
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
What are the roles of mast cells in D. immitis?
Closely related to basophils (tissue version)
Activated & produce amines such as histamine
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?
D. immitis carries Wolbachia (a Rickettsial bacterium) which plays a role in neutrophil-induced inflammation seen in heartworm infection
Outline Caval Syndrome
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
Outline the diagnostic tests used for D. Immitis
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
Discuss the limitations of diagnostic tests
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)
What are the treatments available for D immitis
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.
