6.13 Spirurid Nematodes Flashcards
The Spiruridia order includes what worms
spirurids, filarids, guinea worm (Dracunulus)
what is the location of most Spiruridia
stomach worms, but also connective tissue and eyes
what is the stomach worm of dogs
Physaloptera
what is the stomach worm of dogs and cats
Spirocerca
what are the eye worms
Thelazia
what are the stomach worms of horses
Habronema/Draschia
All Spirurids have (direct/indirect) lifecycles and use ________________ hosts
indirect; arthropodan intermediate (also paratenic)
what are the migrations of Spirurids
simple (no tracheal or somatic and therefore no vertical transmission)
do Spirurids have a relatively long or short PPP
long
what are the intermediate hosts of horse stomach worms (Habronema/Draschia)
muscid flies: house flies and stable flies
describe the lifecycle of Habronema/Draschia
stable flies or house flies pick up larvae -> L3 or the flies are ingested by the horse -> mucosal migration in the gastric pits produces adults
what is the pathogenesis of Habronema and Draschia
Habronema invades the mucosa, causing chronic gastritis
Draschia invades the submucosa, forming tumor-like caseous nodules
T/F the gastritis and tumor-like nodules formed by Habronema and Draschia are responsible for the main disease
F; it is the larvae that cause the main burden of disease
Describe the pathogenesis and clinical signs of Habronema/Draschia megastoma
occurs in an immune host when flies lay larvae on the skin or conjunctiva that then attempt to migrate -> granulomatous inflammation activated by host -> inflammatory lesion produces sore -> weeping of sore attracts more flies -> propagation of the problem
can Draschia or Habronema be treated? with what?
Draschia cannot due to the tumor-like lesions
Habronema can be with moxidectin or ivermectin
Habronema and Draschia in the skin can be treated with ivermectin
what are the general features of all filarid nematodes
- host-specific
- require a blood-sucking insect as an intermediate host
- generally infect CT or body cavities
- long, slender adults
- have microfilaria (pre-L1) stage
describe the pathogenesis and disease caused by Guinea Worm (Dracunulus)
adults live in the connective tissues of the legs -> creates hot blistering lesion -> when host puts their leg in water to relief the burning the female contracts uterus to release eggs -> intermediate host takes up eggs within the water -> intermediate host ingested
what is the intermediate and definitive host of Acanthocheilonema reconditum
fleas; dogs
where are adult Acanthocheilonema reconditum found
CT
what is the morphology of Acanthocheilonema reconditum
- adults
- microfilaria
adults are up to 5cm, slender
microfilaria parallel-sided anterior end
describe the lifecycle of Acanthocheilonema reconditum
microfilaria in the blood of infected dogs -> fleas ingest microfilaria -> develop to L3 within the flea -> re-enters dog (grooming) -> adults in CT -> microfilaria produced by adults
what is the pathogenesis and clinical signs of Acanthocheilonema reconditum
non-pathogenic and no clinical signs
what are the IH and DH of Dirofilaria immitis
IH: mosquitos
DH: dogs, cats, ferrets, wild canids, seals, sea lions, humans
what is the location of adult Dirofilaria immitis
right caudal lobar artery; other branches of pulmonary arteries; right ventricle in heavy infections
what is the morphology of adult and microfilaria Dirofilaria immitis
adults: slender, up to 35cm
microfilaria: tapered anterior end
how can you tell apart male vs female Dirofilaria immitis
males have a curly tail
how can you distinguish Acanthocheilonema reconditum and Dirofilaria immitis
A. reconditum does not taper at the anterior end whereas D. immitis does; D. immitis makes more serpentine movements
what is the life cycle of Dirofilaria immitis
microfilaria in blood of host -> mosquito ingests microfilaria -> microfilaria develop to L3 in the mosquito under the correct conditions -> L3 move to the proboscis -> transmitted with next blood meal -> larvae move subcutaneously and lodge in the pulmonary circulation -> mature in the pulmonary arteries
what environmental conditions are needed for Dirofilaria immitis to develop in the mosquito
above 14 C for at least 7 days
when is heartworm transmission season in Canada
June - Oct
what is the pathogenesis of heartworm (assuming in a patient in an endemic area in the South)
arteritis in the pulmonary circulation; dead worms produce thromboemboli in the lung capillaries and arterioles -> inflammation
Overall: increased vascular resistance and pulmonary hypertension
Pulmonary hypertension produces right sided hypertrophy and CHF
Congestion can produce liver damage
what is the presentation of heartworm in most dogs in Canada
asymptomatic
what are the ways to diagnose heartworm
- antigen test
- Knotts test or Difil test for microfilaria
what is an important caveat to the test for heartworm:
- antigen
- microfilaria
antigen: most depend on antigen from reproductively active females (will not see if no females, senescent females, single worm infection, or prepatent period)
microfilaria: some dogs amicrofilaremic but infected
what are the ways to treat Dirofilaria immitis
- adulticide (Immiticide)
- surgery
- microfilaricides (ivermectin, milbemycin)
- prevention (ivermecin, milbemycin)
describe heartworm in cats
- very rare, more common in highly endemic regions
- more extensive clinical signs with fewer worms (chronic tachypnea, coughing, abnormal lung sounds, vomiting)
- usually amicrofilaremic
