cardiovascular parasites Flashcards
what factors affect the distribution of dirofilaria immitis
- maturation of microfilariae to infective L3 requires 2 weeks >27 degrees celsius and the temperature should not be below 14C
- mosquito breeding on water
- the presence of susceptible hosts
- mosquite species which support the microfilariae
describe the lifecycle of dirofilaria immitis
list the clinical signs of cardiopulmonary disease followinf dirofilaria immitis infection
- narrowing of pulmonary artery
- exercise intolerance
- hydrothorax
- hydroperitoneum
- chronic cough
- dyspnoea
- haemoptysis
- eosinophilia in lung
- oedema in lung parenchyma
Describe how D.immitis infection in the pulmonary artery leads to pulmonary hypertension
- Adult D. immitis in the pulmonary artery.
- Disruption of (inner lining) leads to platelet (Thrombocyte) influx and production of platelet derived growth factor (PDGF).
- PDGF increases proliferation of medial smooth muscle cells and fibroblasts.
Therefore hypertension (HBP) is NOT caused by blockage but by hypertrophy of the medial layer.
Outline the roles of different immune cells in parasitic disease
- eosinophils are important in parasitic and allergic diseases. increased numbers occur in blood and tracheal washes during cardiorespiratory parasitism. they migrate from blood to tissue
- basophils are activated if antigen enters the bloof. they degranulate at surface of blood borne parasites
- mast cells are the tissue version of basophils and are activated and produce amines such as histamine. they are tissue fixed and activated in parasitic infection
Why are neutrophils seen in the walls of the pulmonary artery during heartworm disease of dogs?
Neutrophils respond to bacteria and fungal infections.
D. immitis carries Woolbachia and some studies have suggested that Woolbachia may also play some role in
neutrophil-induced inflammation seen in heartworm infection. Antibiotics can
be used to kill the bacteria which can kill the nematode.
What is Caval syndrome? What are the main clinical signs?
Caval syndrome is the most serious form of heartworm. Large worm burden in the right atrium and posterior vena cava- complete obstruction.
This results in an increased venous pressure which damages liver parenchyma. Damaged liver parenchyma, causing increased cholesterol content of erythrocyte membranes leading to fragility and haemolysis (RBCs rupture).
Resulting in severe (*regenerative) anaemia (many immature/nucleated red cells may be seen in blood as *erythrocytes are replace- to try to compensate for the blood loss).
Caval syndrome is an emergency.
- Erythrocyte haemolysis leads to haemoglobinaemia (free haemoglobin in blood) and bilirubinaemia (bilirubin in blood) clinical signs include haemoglobinuria (blood in urine) and jaundice.
The dog may suddenly collapse/die.
What diagnostic testing options are there for heartworm?
- CBC (complete blood count)
- Knotts test/milipore filter
- thoracic rads
- electrocardiogram/echocardiogram
- arteriogram
- indirect fluorescent antibody
- ELISA
- tracheal wash
what are the limitations of the diganostic tests for heart worm
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 mayh be similar to other diseases
ELISA only adult female antigens detected. false negatives occur if immature females present or male only infection
no test is definitive
What are the treatment options for heartworm disease in dogs?
Adult worms: Melarsomine dihydrochloride (Immiticide), Thiacetarsemide (Caparsolate).
Microfilariae:
- Ivermectin (contraindicated in CNS pathology)
- Milbemycin.
- Both can be used as preventatives (Ivermectin=Heartguard, Milbemycin = Interceptor).
Why must adult heartworms be treated before microfilariae? How can this be done?
- Adults must be removed before treatment of microfilariae but dead worms may induce significant inflammatory immune reactions.
- This can lead to pulmonary thromboembolism (clot in the pulmonary artery).
- Disseminated intravascular coagulation (DIC)- microcoagulation/very high platelet counts/endothelial damage.
- Probably some embolisation is expected following adulticide treatment.
Surgical removal- in very heavy infections adulticide treatment may lead to severe pathology (dead worms may cause thromboembolism). During caval syndrome worms need to be removed very quickly.
How can D. reconditum microfilariae be distinguished from D. immitis microfilariae? Why would this need to be done?
Dipetalonema reconditum is common in USA, 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.
Significance probably in false positive D. immitis results. Acid phosphatase test determines species- D. immitis have two spots of staining whereas D. reconditum is stained throughout.
How is D.immitis infection different in cats than dogs?
- Cats are much more resistant than dogs but are still susceptible- not really the natural host- ectopic infection- not necessarily infecting the heart.
- Increased immune response with fewer adult worms- as not the natural host. 1-6 rather than >30.
- Microfilariae often not detected in blood smears.
- Adult worms do not live as long in cats (2-3 years) as in dogs (5-7 years).
- The overall effect is that cats are not as good a reservoir (natural host) of D. immitis but very few worms can cause significant disease.
How is D.immitis diagnosed in cats? Why are there complications?
- 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 (called nocturnal periodicity). Single sex infections occur more in cats (no microfilariae produced).
- Clinically infected cat may have very low worm burdens. Therefore ELISA analysis to detect antigen may give false negative. But as very few worms may cause significant pathology, the ELISA developed for cats measures antibody to parasite.
Radiographs and echocardiograms can be used.
As D.immitis infections in cats predominantly presents as lung disease tracheal washes and swabs can be carried out.
therapy does little to help the cat. management is directed at alleviating signs, with emphasis on prevention for all
How is the ELISA analysis of microfilariae antibodies carried out in cats? What are the limitations?
- 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 parasite (rather than parasite antigen) (Antibody parasite refers to the antibody produced by the host’s immune system in response to a parasite infection. Parasite antigen, on the other hand, refers to the proteins or other molecules produced by the parasite itself.)
limitations:
- 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 and current/previous infection
therefore less appropriate screening test and should be interpreted in relation ot clinical signs and other diagnostic findings
