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→Life Cycle
==Life Cycle==
==Life Cycle==
D immt adults reach sexual maturtyF in tth plmonary
arteries and right ventricle of the dog. After
mating, the female nematodes rea e immature larvae
(LI or micrflria into the crulation. Mkrofilariae
are eventually ingeste bymosquitoes during
a blood meal. Msqito0ear not o*nya v or but
also an obligatory iemei os
heartworm diease could t be it.
ingested micraoariaae require a perio f maturtion
in the insect, which varies depending on enronmental
conditions. This development canntot otur beow
the threshold temperature of 14C When the cycle
is temporarily suseded until warmer conditions
resume. At an average dily temperature of 30W,
maturation can bte complete in eight days; howr,
maturation takes approximately moe month at an
environmental tempratu Of 18C. Transmission of
infecive larvae is therefore limitd to warm month
and varies depending on geographical location.
also on the season, and this is a key consideration when
screening for the disease or planning a chemoprophylactic
schedule.
Although heartworm disease has been diagnosed in
the UK in dogs imported from abroad, the disease is
unlikely to spread in this country despite the presence of
potential vectors and a large canine population. In fact,
the low average daily temperature does not allow larval
maturation within the mosquito, even in summertime.
In the mst mir o-aseo
larva stage(V12 ad,eventaly,tothe inetv 0~tg
.When the 130ta s drelav
from the tubules to the ines
subseqnt blood meal on an ap rt enter
the bite wound, colnising the local connetivethisses
Atr aoxi one vwek, the larvae matuWe fom
L3 to L4 and, follobwig ctinu migration for two to
three months in the subcutaneous tisse reac the final
stage of immature aduts (1. The 1 larvae penetrate
a systeic vein; and migrate to the right heart and pulmonary
ateries ithin a few days they Mature
and mate after around6 tree to six mont releasing
microfilariae into th cicltion to complet the biological
cyle. The average prepatent period about six
months in dog and eigh onths in cat.
Adult D immitisay survive for up to five year in
dg; inats; the w0orms p more slowlyad surve
f*r approximat two years. The slower devlopmnent
Mosquito vector species acquire the first stage larvae (microfilariae) while feeding on an infected host. Development of microfilariae to the second larval stage (L2) and to the infective third stage (L3) occurs within the mosquito in ~1-4 wk, depending on environmental temperatures. This development phase requires the shortest time when the ambient temperature is >86°F (30°C). When mature, the infective larvae migrate to the labium of the mosquito. As the mosquito feeds, the infective larvae erupt through the tip of the labium with a small amount of hemolymph onto the host’s skin. The larvae migrate into the bite wound, beginning the mammalian portion of their life cycle. A typical Aedes mosquito is only capable of surviving the developmental phase of small numbers of HW larvae, usually <10 larvae per mosquito.
Mosquito vector species acquire the first stage larvae (microfilariae) while feeding on an infected host. Development of microfilariae to the second larval stage (L2) and to the infective third stage (L3) occurs within the mosquito in ~1-4 wk, depending on environmental temperatures. This development phase requires the shortest time when the ambient temperature is >86°F (30°C). When mature, the infective larvae migrate to the labium of the mosquito. As the mosquito feeds, the infective larvae erupt through the tip of the labium with a small amount of hemolymph onto the host’s skin. The larvae migrate into the bite wound, beginning the mammalian portion of their life cycle. A typical Aedes mosquito is only capable of surviving the developmental phase of small numbers of HW larvae, usually <10 larvae per mosquito.
In canids and other susceptible hosts, infective larvae (L3) molt into a fourth stage (L4) in 2-3 days. After remaining in the subcutaneous tissue for close to 2 mo, they molt into young adults (L5) that migrate through host tissue, arriving in the pulmonary arteries ~50 days later. Adult worms (males ~15 cm in length, females ~25 cm) develop primarily in the pulmonary arteries of the caudal lung lobes over the next 2-3 mo. They reside primarily in the pulmonary arteries but can move into the right ventricle when the worm burden is high. Microfilariae are produced by gravid females ~6-7 mo postinfection.
In canids and other susceptible hosts, infective larvae (L3) molt into a fourth stage (L4) in 2-3 days. After remaining in the subcutaneous tissue for close to 2 mo, they molt into young adults (L5) that migrate through host tissue, arriving in the pulmonary arteries ~50 days later. Adult worms (males ~15 cm in length, females ~25 cm) develop primarily in the pulmonary arteries of the caudal lung lobes over the next 2-3 mo. They reside primarily in the pulmonary arteries but can move into the right ventricle when the worm burden is high. Microfilariae are produced by gravid females ~6-7 mo postinfection.