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Parasitology > Filarids > Flashcards

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
Q

Dirofilaria immitis - required hosts

A
  • DH: susceptible population
  • IH: susceptible mosquito species
  • reservoir hosts
  • stable mosquito population: anopheles, aedes, culex
26
Q

Climate supporting parasite development in IH

A
  • at least 2 weeks with temperatures >27 C (80 F)

- **no larval development if temperature <14 C (57 F)

27
Q

Heartworm pathogenesis in dogs

A

Higher worm burden

  • more severe lung/heart disease
  • nearly all hws reside in lower caudal pulmonary arteries
  • higher numbers = presence in right heart
28
Q

Pathologic changes

A

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
Q

Cardiopulmonary disease in dogs

A

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
Q

Pulmonary hypertension in dogs

A

Induces dilatation of right ventricle

- compensatory myocardial hypertrophy

31
Q

Congestive heart failure

A

Occurs in severe cases

  • acute or gradual
  • ascites
  • hydrothorax
  • hydropericardium
32
Q

Parasites in heart may trigger ________

A

Mechanical valvular damage/endocarditis

33
Q

Progression of clinical signs

A

Early: inapparent
Mild: cough
Moderate: cough, exercise intolerance, abnormal lung sounds
Severe: dyspnea, hepatomegaly, syncope, ascites, abnormal heart sounds, death

34
Q

What are the 3 forms of heartworm treatment in dogs?

A
  • adulticide therapy
  • elimination of microfilariae
  • preventatives
35
Q

Adulticide therapy

A

Approved

  • melarsomine dihydrocloride
  • effective on worms >4 mo post infection
  • requires close monitoring
36
Q

Elimination of microfilariae

A 
Macrocyclic lactones (off label in HW pos dogs)
- after recovery from adulticide treatment
37
Q

Preventatives

A

Macrocyclic lactones

  • ivermcetin
  • milbemycin oxime
  • selamectin
  • moxidectin
  • all effective against L3 and L4*
38
Q

Caval syndrome

A

Acute disease/clinical emergency

  • large numbers of worms in the right atrium, tricuspid valve, caudal vena cava
  • increased venous pressure in liver
39
Q

Caval syndrome clinical signs

A
  • acute onset of weakness/anorexia
  • dyspnea
  • collapse
  • pale mucous membranes +/- jaundice
  • bilirubinemia
  • bilirubinuria
  • hemoglobinuria
40
Q

Heartworm prevention is only effective against

A

Developing larvae in the tissue

- 2 1/2 months

41
Q

Heartworm life cycle in a cat

A

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
Q

Antigen of microfilaria is produced from the _______

A

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
Q

What are the 2 stages of HW disease in cats?

A 
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
Q

Clinical signs of acute infection in cats

A

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
Q

________ are seldom found in cats

A

Circulating microfilariae

46
Q

Heartworm preventative in felines

A

Macrocyclic lactones: ivermectin, selemectin, milbemycin oxime, moxidectin

  • effective against L3 and L4
  • cats are rarely microfilaremic
  • safe even in hw positive cats
47
Q

Wolbachia pipientis

A

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
Q

Doxycycline

A

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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