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Filarids Flashcards

1
Q

What are the 4 families within Filarids?

A
  • Onchocerca cervicalis
  • Onchocerca lupi
  • Acanthocheilonema
  • Dirofilaria immitis
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2
Q

Filarids are in the order ______

A

Spirurida

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3
Q

Filarid - general characteristics

A
  • indirect life cycle

- intermediate host: blood sucking arthropods (biting flies, flea, tick, female mosquitoes) –> produce microfilariae

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4
Q

Vermiform embryo

A

Contains only cell clusters as primordia

  • pre L1 stages
  • ingested by IH
  • L1 to L2 to L3 in IH
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5
Q

_____ stage contains clearly recognizable organs

A

L1

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6
Q

Microfilariae are an example of _______

A

Vermiform embryo

  • develop into larvae only after it has been ingested by IH
  • if no ingestion of IH occurs, then the larval stages do not develop
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7
Q

______ is generally the infective stage

A

L3

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8
Q

Onchocerca cervicalis hosts

A

Indirect life cycle

  • DH: equids
  • IH: culicoides spp (biting midges)
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9
Q

Onchocerca cervicalis life cycle

A 
DH: equid 
- PPP = 16 months!!
- L3 infects DH with next blood meal of IH
- L3 --> nuchal ligament
- adults in nuchal ligament
- microfilariae (subdermal CT)
IH: blood sucking arthropod females 
- 2-3 weeks
- ingest MF
- pre L1 stages (VE)
- L2
- L3 (infective stage)
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10
Q

Onchocerca cervicalis - pathology

A 
Microfilaria
- distributed in dermis and other subdermal CT
- ocular conjunctivae
Larvae
- nuchal ligament
Adults
- unnoticed/nonpathogenic
- woven deep in the nuchal ligament
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11
Q

Onchocercal dermatitis

A

Antigen released from dying microfilaria

  • older animals (>5 yr)
  • summer and winter
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12
Q

Onchocerca cervicalis - diagnosis

A

Skin biopsy (full thickness)
- tissue minced in isotonic saline for hours
- microfilariae stained with methylene blue after removal of skin pieces
- examine microfilariae
Differential –> hypersensitivity to biting flies

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13
Q

Onchocerca cervicalis - treatment

A

No treatment effective against adults!!

- ivermectin and moxidectin for use against microfilariae

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14
Q

Onchocerca ______ infects canids

A

lupi

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15
Q

Canine onchocercosis

A

Mainly distributed in the western US

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16
Q

Onchocerca lupi - general characteristics

A

DH: dogs and cats
- identified in US in 2013
- cases in humans, unknown transmission
Patent infections: large number of microfilaria

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17
Q

Onchocerca lupi causes acute and chronic _______

A

Ocular disease

- mass in eye or nodule in retrobulbar space

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18
Q

Canine onchocercosis

A
  • conjuctivitis
  • discomfort
  • periorbital swelling
  • exophthalmos
  • photophobia
  • lacrimation
  • discharge
  • periocular tissue
  • granulomatous nodules
  • cysts
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19
Q

Acanthocheilonema reconditum - hosts

A

Indirect life cycle (PPP: 2-3 months)
DH: dogs (adults, subq tissue)
IH: fleas (c. felis/canis, pulex irritans)
Microfilaria: blood
- ingested by IH –> L1-L3 in 1-2 weeks –> L3 to DH when IH feeds

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20
Q

Acanthocheilonema reconditum - clinical signs

A

Nonpathogenic!

  • importance in differentiating microfilaria (dirofilaria immitis vs a. reconditum)
  • do not treat for A. reconditum
  • flea control to reduce prevalence
21
Q

Dirofilaria immitis - hosts

A

DH: domestic dog, some cat, rare in ferrets
IH: mosquitoes
Dead-end hosts: bears, raccoons, beavers, humans*
Reservoir hosts: red wolf, foxes, coyotes, wolverines, sea lions, wild felids

22
Q

Dirofilaria immitis in humans

A

Leads to coin lesions in lungs

- may be misinterpreted as neoplasia

23
Q

Dirofilaria immitis - life cycle

A

Mosquito takes a blood meal (L3 enters skin –> infective) –> L4 migrate toward thorax, circulatory system –> adults in pulmonary arteries and right heart –> female produces microfilariae in 180 days –> mosquito takes blood meal (ingests MF) –> L1 –> L2 –> L3, migrates to mouth parts

24
Q

Where are adults of D. immitis located?

A

Pulmonary arteries and right heart

25
Dirofilaria immitis - required hosts
- DH: susceptible population - IH: susceptible mosquito species - reservoir hosts - stable mosquito population: anopheles, aedes, culex
26
Climate supporting parasite development in IH
- at least 2 weeks with temperatures >27 C (80 F) | - **no larval development if temperature <14 C (57 F)
27
Heartworm pathogenesis in dogs
Higher worm burden - more severe lung/heart disease - nearly all hws reside in lower caudal pulmonary arteries - higher numbers = presence in right heart
28
Pathologic changes
Early - due to inflammatory processes in/around arteries of lower lungs Late - heart may enlarge and become weakened due to increased workload - congestive heart failure Very active/working dogs - severe disease with fewer heartworms
29
Cardiopulmonary disease in dogs
Primarily due to adults in pulmonary arteries!! - narrowing/occlusion of pulmonary arteries - disrupts intima: attracts platelets, favors thrombus formation, proliferation of medial smooth muscle cells, arterial stenosis - leads to pulmonary hypertension
30
Pulmonary hypertension in dogs
Induces dilatation of right ventricle | - compensatory myocardial hypertrophy
31
Congestive heart failure
Occurs in severe cases - acute or gradual - ascites - hydrothorax - hydropericardium
32
Parasites in heart may trigger ________
Mechanical valvular damage/endocarditis
33
Progression of clinical signs
Early: inapparent Mild: cough Moderate: cough, exercise intolerance, abnormal lung sounds Severe: dyspnea, hepatomegaly, syncope, ascites, abnormal heart sounds, death
34
What are the 3 forms of heartworm treatment in dogs?
- adulticide therapy - elimination of microfilariae - preventatives
35
Adulticide therapy
Approved - melarsomine dihydrocloride - effective on worms >4 mo post infection - requires close monitoring
36
Elimination of microfilariae
``` Macrocyclic lactones (off label in HW pos dogs) - after recovery from adulticide treatment ```
37
Preventatives
Macrocyclic lactones - ivermcetin - milbemycin oxime - selamectin - moxidectin * all effective against L3 and L4*
38
Caval syndrome
Acute disease/clinical emergency - large numbers of worms in the right atrium, tricuspid valve, caudal vena cava - increased venous pressure in liver
39
Caval syndrome clinical signs
- acute onset of weakness/anorexia - dyspnea - collapse - pale mucous membranes +/- jaundice - bilirubinemia - bilirubinuria - hemoglobinuria
40
Heartworm prevention is only effective against
Developing larvae in the tissue | - 2 1/2 months
41
Heartworm life cycle in a cat
PPP: 7-8 months - infected mosquito takes a blood meal --> L3 enters skin --> L3 molt to L4; L4 molt to adult --> adults arrive in pulmonary artery (3-4 months) - adults in pulmonary artery and heart (1-3 worms) --> adults live 2-3 years --> female produces MF (microfilaremia only for 1 month!!) --> adults die
42
Antigen of microfilaria is produced from the _______
Uterus of a female | - if cat is infected only with males, then diagnostic tests will not pick up HW, or you will not see clinical disease
43
What are the 2 stages of HW disease in cats?
``` When parasites arrive in pulmonary vasculature - 3-4 months post infection - intense inflammation - large proportion of juveniles die When adult HW die - inflammation - thromboemboli - infarction - respiratory failure possible ```
44
Clinical signs of acute infection in cats
Subside as worms mature - histopathologic lesions evident even when cat clears infection - occlusive medial hypertrophy of small pulmonary arterioles - changes noted in bronchi, bronchioles, alveoli and pulmonary arteries
45
________ are seldom found in cats
Circulating microfilariae
46
Heartworm preventative in felines
Macrocyclic lactones: ivermectin, selemectin, milbemycin oxime, moxidectin - effective against L3 and L4 - cats are rarely microfilaremic - safe even in hw positive cats
47
Wolbachia pipientis
Intracellular gram-neg bacteria - role in pathogenesis and host immune response - identify components that interact with host immune system - necessary for D. immitis to reproduce/thrive --> produce metabolites, contribute to disease process
48
Doxycycline
Pretreated HW pos dog with ivermectin and doxy - prior to receiving melarsomine - less pulmonary pathology normally associate with hw death - 78% reduction in hw numbers using only ivermectin and doxy - doxy administration at 10mg/kg bid for 4 weeks shown to eliminate over 90% of wolbachia organisms, levels remain low for 3-4 months

Parasitology (28 decks)

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