Heartworms

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Heartworms
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Dirofilaria immitis
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The dog is the primary host of Dirofilaria
immitis.
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Other Hosts Cats are sporadic hosts, 4 in
Louisiana surveys. Most are occult, but there can
be an acute seasonal pulmonary disease. The fox
and coyote are possible reservoirs. The ferret
and sea lion are highly susceptible. Man can
develop coin lesions with an occult infection
of L4-L5 only. D. tenuis, a subcutaneous filarid
of raccoons, causes skin nodules in humans.
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Vectors Thirty mosquito spp. have been reported
as vectors. Culex quincifasciatus is the main
vector in Louisiana. Aedes albopictus (asian
tiger mosquito) is now of equal importance in the
transmission of D. immitis. There is a 10-14 day
development period in the mosquito in warm
weather. At 57ºF microfilariae (mf) develop in
the malphigian tubules of the mosquito, and at
65 ºF can develop and molt from L1-L3.
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Life Cycle Microfilariae of an infected dog are
picked up by a mosquito upon feeding.
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Life Cycle Microfilaria molt from the L1 stage to
the L3 stage within the mosquito.
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Mf become sausage stage and molt in malphigian
tubules. L3 escape to hemocoel fluids.
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Life Cycle L3 is deposited in the hemolymph via
the proboscis upon another meal by the mosquito,
then penetrate via puncture wound.
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Life Cycle
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Life Cycle
At 10-14 days after infection, L3 molts to L4 in
the SQ tissues. By 60-70 days, L4 will molt to L5
within the muscle fascia.
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Life Cycle
At 3-4 months, the worms enter the heart as L5,
still at a small size of 1-3 cm.
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Life Cycle
5-8 months is the prepatent period. After this
time, microfilaria will be present in the blood
with the presence of male and female worms.
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Adults are 10-30 cm. Normally they are 15 cm with
a corkscrew tail. Adults live about 5 years in
the dog and less than 2 years in the cat.
Microfilaria live 1-2 years in the dog with no
microfilaricide treatment.
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Dogs Chronic Thromboembolic disease results.
Glomerulonephiritis, DIC, Pulmonary Infiltrates
with Eosinophilia, Post-Cava Syndrome are less
common. Cats Acute Pulmonary Asthmatic disease
may result
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Radiographic view of Heartworm disease
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Microfilariae can be detected via direct smear
(an underestimated screening test),
microhematocrit, Knotts test, or filter test
methods.
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Upon examination of microfilariae, a distinction
must be made between infection of Dirofilaria
immitis, or the non-pathogenic Dipetalonema
reconditum.
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To distinguish between Dirofilaria and
Dipetalonema, the above factors must be
considered upon examination.
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Dirofilaria Dipetalonema Length 286-340um
246-293um (by knotts) Width 6.0-7.2um
4.5-5.8um Anterior tapered
blunt Posterior straight 30 hooked
Body straight often curved
No./ml numerous(1-10,000) less numerous
(1-1,000) Movement undulate in situ move across
field R(G) cells 1-2-1 pattern 1-3
pattern Rectal or genital cells are near
posterior of microfilariae.
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Treatment Adulticidal drugs Organic arsenicals
that affect rapidly multiplying digestive cells.
Worms starve to death in 7-10 days, at which time
they embolize to the lungs for up to 4 weeks. If
this occurs, control clinical pulmonary embolism
with diminishing anti-inflammatory doses of
corticosteroids. Can use Caparsolate or
Immiticide.
Microfilaricide 3-4 weeks post adulticide
treatment is safe for microfilaria treatment.
Drugs to use are Ivermectin, Milbemycin, or
Diethylcarbamazine HCL.
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Heartworm Prevention
Ivermectin and Milbemycin Pharmacology Macrocyclic
lactone structures Produced by same genera of
soil dwelling organisms Affect similar spectrum
of parasitic organisms Share similar mode of
action Structural modification affect biological
profiles
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Heartworm Prevention Interceptor
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Heartworm Prevention
RevolutionTM (selamectin) First topically applied
endectocide First topical heartworm
preventative Broad-spectrum activity against
endo- and ectoparasites A novel semi-synthetic
avermectin Low volume, easy to apply, topical
formulation Quick drying/cosmetically
acceptable Packed in color-coded, multidose
tubes Water fast two hours after application
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Revolution Spectrum of Protection
Dog Cat Adult fleas
Flea eggs Heartworm
Ear mites Sarcoptic mites
Tick (D. variabilis) Hookworm (A.
tubaeforme) Roundworm (T.cati)