Lecture 3: Nematodes (heartworms) Flashcards
canine heartworm
dirofilaria immitis
adult dirofilaria immitis are found where
right ventricle, pulmonary arteries
filaria do not produce eggs but
free living larval stages called microfilaria
vector/IH of dirofilaria immitis
mosquitoes
must differentiate heartworm MFF from
acanthocheilonema reconditum (filaria trans by fleas but not considered a pathogen)
number of MFF in blood of acanthocheilonema vs dirofilaria
few - acantho
many - dirofilaria
motion of dirofilaria vs acanthocheilonema MFF
Dirofilaria are stationary, wiggle and stay in view
acanthocheilonema is progressive and will move out of view
shape of dirofilaria vs acanthocheilonema
acantho is curved, thinner, shorter, has curved thin tail
dirofilaria is straight with a tapered head, longer
occult infections
dog harbors male and/or female adults
single sex
low numbers
“hidden” infection = MFF NOT detectable in blood
best way to dx occult HW infection
Ag test
when are dirofilaria MFF most active in circulation
nocturnal and incomplete periodicity (never disappear from peripheral blood)
how many mosquito spp are common vectors for HW
14
__ are released by the female worm, mosquito feeds on dog and picks this stage up
MFF
MFF develop to infective __ in the mosquito in about 8 days (temp dependent)
L3 larvae
L3 larvae are deposited at the skin surface when mosquito takes blood meal; L3 enter DH via
mosquito’s bite wound
larvae migrate and molt and eventually mature in the
heart or lungs
prepatent period for dirofilaria immitis
6-7mo
what stage do the preventatives we give monthly affect
L3 the first 3d in circulation while molting to L4
worms are not detectable consistently using most test procedures until they are __ old
6-6.5mo
Ag positive test but do not see MFF
gravid female is detected by Ag test before birthing MFF
how many spp of mosquitos are known to transmit HW
24
Disease in dogs is mainly due to the
adult worms in the PA
rough internal surface of PA is termed
villous endarteritis
changes in circulation caused by HW
Vascular resistance (right ventricle hypertrophy) decreased CO (exercise intoleracne, liver and kidney dz)
overrun with worms, infect atrium and vena cava
vena cava syndrome
diagnose HW
Detection of Ag and detection of circulating microfilariae
when are most dogs Ag positive that are not on routine preventatives
~7mo PI, can be as early as 5mo
when would dogs who missed a dose of preventative become Ag positive
~9mo PI
pets on macrocyclic lactones may never develop MFF or they are transient in small numbers
what sample do you need for SNAP, witness, Heska POC Ag test
serum, plasma, or whole blood
what is the gold standard HW Ag test
diroCHEK HW Ag test (serum or plasma)
if get a positive on a POC test what should you do next
check for MFF and check a different POC test
what test measures MFF present
modified knotts
who should be tested for HW Ag and when
every dog annually
pets not on preventative dogs over 7mo , retest 7-12 mo after starting prevents
dog misses dose, retest 7-12 mo after restart
AHS guidelines suggest testing at 6 and 12 mo
if switch HW preventatives when should you retest for Ag
4.5 and 9 mo after switch
should you trust HW Ag test results
yes, high sensitivity and specificity
What can cause a positive Ag test but negative MFF test
- young infection, no circ MFF yet
- using preventatives w/o removing adults
- female only infection
- immune mediated occult
- failure to use MFF concentration test
what can cause a negative Ag test but positive MFF test
- different spp of MFF
- MFF aquired transplacentally
- adults removed or died but still have circulating MFF
- contaminated test
if antigen test is variable and MFF is negative or positive
fluctuating Ag levels (# worms, age worms, quality sample)
what is the susceptibility gap
the early stages are suseptible to macrocyclic lactones
the later stages are susceptible to melarsomine
inbetween no treatment will touch “teenage stage” = susceptibility gap
symbiotic gram negative bacteria related to Ehrlichia that is present in ALL life stages of dirofilaria immitis
Wolbachia pipientis
what do we know about Wolbachia and Dirofilaria
it contributes to pulmonary and renal inflammation, is important for biology and reproductive functions, necessary for worm survival
killing adult worms
melarsomine dihydrochloride (immiticide)
NO activity against worms <4mo
AHS recommends 3 dose protocol
what can help control clinical signs of PTE during HW tx
Steriods
What can help treat wolbachia and weaken HW before immiticide tx
doxycycline
What is a potent preventative that treats MFF but a modified knotts should always be done first to quantify MFF present
moxidectin (advantage multi)
cats infected with HW get what condition
heartworm associated respiratory dz (HARD); vascular and airway dz from death of IMMATURE HW in cats
stage 1 of HARD in cats
immature adults in PA, immune rxn suppressed and cats tolerate the worms
Stage 2 of HARD in cats
worms dying = inflammation and PTE
worms rarely mature in cats
cats IS is killing the worms causing inflammation and death usually occurs from __ not the worms
PTE
dz in canines vs felines depends on
dogs: number of worms and size of dog
cat: few worms cause dz
worms are __ lived in dogs/cats
long (dogs)
short (cats)
MFF in cats
usually amicrofilaremic
what organs are affected in dogs v cats
dogs: hear and lungs
cats: lungs
treatment of HW in dogs vs cats
dogs: treatment available
cats: only symptomatic tx, cannot use melarsomine in cats
