Filarids Flashcards
What are the 4 families within Filarids?
- Onchocerca cervicalis
- Onchocerca lupi
- Acanthocheilonema
- Dirofilaria immitis
Filarids are in the order ______
Spirurida
Filarid - general characteristics
- indirect life cycle
- intermediate host: blood sucking arthropods (biting flies, flea, tick, female mosquitoes) –> produce microfilariae
Vermiform embryo
Contains only cell clusters as primordia
- pre L1 stages
- ingested by IH
- L1 to L2 to L3 in IH
_____ stage contains clearly recognizable organs
L1
Microfilariae are an example of _______
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
______ is generally the infective stage
L3
Onchocerca cervicalis hosts
Indirect life cycle
- DH: equids
- IH: culicoides spp (biting midges)
Onchocerca cervicalis life cycle
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)
Onchocerca cervicalis - pathology
Microfilaria - distributed in dermis and other subdermal CT - ocular conjunctivae Larvae - nuchal ligament Adults - unnoticed/nonpathogenic - woven deep in the nuchal ligament
Onchocercal dermatitis
Antigen released from dying microfilaria
- older animals (>5 yr)
- summer and winter
Onchocerca cervicalis - diagnosis
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
Onchocerca cervicalis - treatment
No treatment effective against adults!!
- ivermectin and moxidectin for use against microfilariae
Onchocerca ______ infects canids
lupi
Canine onchocercosis
Mainly distributed in the western US
Onchocerca lupi - general characteristics
DH: dogs and cats
- identified in US in 2013
- cases in humans, unknown transmission
Patent infections: large number of microfilaria
Onchocerca lupi causes acute and chronic _______
Ocular disease
- mass in eye or nodule in retrobulbar space
Canine onchocercosis
- conjuctivitis
- discomfort
- periorbital swelling
- exophthalmos
- photophobia
- lacrimation
- discharge
- periocular tissue
- granulomatous nodules
- cysts
Acanthocheilonema reconditum - hosts
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
Acanthocheilonema reconditum - clinical signs
Nonpathogenic!
- importance in differentiating microfilaria (dirofilaria immitis vs a. reconditum)
- do not treat for A. reconditum
- flea control to reduce prevalence
Dirofilaria immitis - hosts
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
Dirofilaria immitis in humans
Leads to coin lesions in lungs
- may be misinterpreted as neoplasia
Dirofilaria immitis - life cycle
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
Where are adults of D. immitis located?
Pulmonary arteries and right heart
Dirofilaria immitis - required hosts
- DH: susceptible population
- IH: susceptible mosquito species
- reservoir hosts
- stable mosquito population: anopheles, aedes, culex
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)
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
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
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
Pulmonary hypertension in dogs
Induces dilatation of right ventricle
- compensatory myocardial hypertrophy
Congestive heart failure
Occurs in severe cases
- acute or gradual
- ascites
- hydrothorax
- hydropericardium
Parasites in heart may trigger ________
Mechanical valvular damage/endocarditis
Progression of clinical signs
Early: inapparent
Mild: cough
Moderate: cough, exercise intolerance, abnormal lung sounds
Severe: dyspnea, hepatomegaly, syncope, ascites, abnormal heart sounds, death
What are the 3 forms of heartworm treatment in dogs?
- adulticide therapy
- elimination of microfilariae
- preventatives
Adulticide therapy
Approved
- melarsomine dihydrocloride
- effective on worms >4 mo post infection
- requires close monitoring
Elimination of microfilariae
Macrocyclic lactones (off label in HW pos dogs) - after recovery from adulticide treatment
Preventatives
Macrocyclic lactones
- ivermcetin
- milbemycin oxime
- selamectin
- moxidectin
- all effective against L3 and L4*
Caval syndrome
Acute disease/clinical emergency
- large numbers of worms in the right atrium, tricuspid valve, caudal vena cava
- increased venous pressure in liver
Caval syndrome clinical signs
- acute onset of weakness/anorexia
- dyspnea
- collapse
- pale mucous membranes +/- jaundice
- bilirubinemia
- bilirubinuria
- hemoglobinuria
Heartworm prevention is only effective against
Developing larvae in the tissue
- 2 1/2 months
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
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
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
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
________ are seldom found in cats
Circulating microfilariae
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
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
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
