Download Dirofilaria immitis - Winona State University

Dirofilaria immitis
Jennie Xiong
Senait Gebrehiwot
Taxonomy
Kingdom: Animalia
Phylum: Nemathelminthes
Class: Nematoda
Subclass: Spiruria
Order: Spirurida
Family: Filariidae
Genus: Dirofilaria
Species: immitis
Penial spicules
Information
Parasitic in the right side of the heart and
pulmonary artery of dogs and other
mammals throughout most of the world
 Found in humans including in US but do not
mature in humans
 Neither mature worms nor eggs have been
detected in humans
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The Wolbachia factor
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Wolbachia is a bacterium that lives in endosymbiosis within adult
heartworms
They are beneficial to worms reproduction in embryogenesis.
When a dog is treated with antibiotic to kill the Wolbachia, the
adult worm either dies or becomes sterile
Wolbachia can be killed by mild antibiotics like tetracycline.
The large part of pathogenesis during filarial infections comes
from the immune response to the bacteria Wolbachia
In humans inflammatory responses may show symptom of
infection when the worms die and the body’s immune system tries
to get rid of the bacteria.
When heartworms die, Wolbachia bacteria can still cause
embolism and shock to the host organism
Question #1
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In what way would treating heartworm
infected dogs with antibiotics like
tetracycline be beneficial?
It kills the Wolbachia that lives in the worm
and helps either by killing the worm or at
least sterilizing it.
Geographic Distribution
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World wide
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Prefers mild and warm
climates
United States, Italy,
Japan, Canada,
Australia, France,
Armenia, Brazil,
Venezuela, Philippines,
Malaysia, New Guinea,
Tahiti, Sierra Leone and
China
U.S. Distribution
Most common along Atlantic and Gulf Coasts
Morphology
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Adult female
25-31 cm long and 11.3 mm wide
 Obtuse posterior
end
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Adult Male
12-20 cm long and
0.7-0.9 mm wide
 Tapering, spirallycoiled posterior end
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Host
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Intermediate Host
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Mosquitoes (many—over to
60 species of mosquitoes)
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Culex pipiens aka house
mosquito – worldwide
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night feeder
plain, brown insect that
breeds freely around
human habitation, laying
egg rafts in tin cans, tires,
cisterns, clogged rain
gutters, and any other
receptacle of water
Aedes species - US
Definitive Host
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Dogs, Cats, Foxes, Wolves,
Coyotes, Ferrets, Seals
Humans (accidental host)
Culex pipiens
Question #2
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How many species of mosquitoes are
capable of transmitting D. immitis?
Which ones are common?
Over 60 species. Culex pipiens and Aedes
species.
Life Cycle
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Adult parasites in chambers of right side of heart and pulmonary artery
Eggs developing in uterus are enclosed in a thin vitelline membrane
As embryo elongates, surrounding membrane stretches to conform as an enclosing sheath
At birth membrane is lost and embryo appears in blood as a sheath less microfilariae
Microfilariae deposited in blood of chambers of right side of the heart and pulmonary artery
then carried through the lungs into a left chambers of heart and into circulation
Mosquito takes blood meal and ingest microfilariae
Microfilariae migrate from intestine within 24 to 36 hours into the Malpighian tubules where
further development and molt form the first to the second stage juvenile occurs
After 9 days they enter the abdominal hemocoel where second molt occurs
Third stage larvae are about 900 um long and appear 10-20 days after entering mosquito
Third stage larvae migrate to mouthparts of mosquito
Infection of dogs occurs while mosquito goes for blood meal
Third stage juveniles escape onto the skin and enter through feeding site
80 days juveniles are in subcutaneous tissues and muscles where third molt takes place 9-12
days after entry
In tissue, fourth stage juveniles attain lengths up to 25 mm and begin entering right side of heat
shortly after the fourth molt 60-70 days after entering the dog
Development to maturity takes 174-223 days at which time microfilariae appear in the blood
Reproductive period exceeds 2 years and may extend to 5 years
Question #3
What is the circulation route for
microfilariae from the adult to the blood
system?
From the right heart (ventricle) to the
pulmonary artery to the lung and to the
heart via pulmonary vein and then out to
the peripheral circulation.
Question #4
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Where do microfilariae come from (what
stage)?
From the adult female heartworm at birth in
either right side of the heart or the
pulmonary artery.
Epidemiology
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Highest prevalence in US corresponds with the highest mosquito
density, along the Mississippi River throughout the Midwestern states,
prevalence among dogs is up to 45%, prevalence is much lower in
western US but can range to 5% in some areas of California and
Oregon
Transmission may occur whenever daily temperature regularly exceeds
57°F (14°C), the threshold for development of juveniles in mosquitoes
Usually in humans, the worms migrate to the lungs instead of the heart.
Here they form a lesion that can be seen on X-rays. There are normally
few symptoms noticed with human heartworm infestation. Surgical
removal of the lung lesion may be performed, if necessary (cysts in
lungs or eyes)
The parasite is spread by mosquitoes and while most of us have
immune systems that successfully fight off the disease, the disease is
sometimes the winner. Immune suppressed people, especially AIDS
and other cancer patients are most susceptible.
Human infection and inflammation is usually related to Wolbachia.
Question #5
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Why is D. immitis prevalence high along
the Mississippi River?
Because of high density of mosquito.
Pathogenesis
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Ig-cleaving protease on surface that cleaves adherent antibodies that are
produced from humans
Can synthesize all classes of complex lipids, including cholesterol
Dangerous pathogen for dogs and although prevalence and worm load are
usually lower in cats, even a few worms can cause serious disease in cats
Clinical signs include respiratory insufficiency, vomiting, chronic cough and
exercise intolerance
Larger worms extending through the openings of the tricuspid and semilunar
valves will prevent efficient operation of those heart valves
Pulmonary arteries show thickening and inflammation of their inner walls
Death may occur from cardiopulmonary failure
In humans symptoms are vague and unpredictable and may include chest
pain, cough, coughing up blood, fever and depression
Dying adult worms passing from the heart into the lungs clog arteries, lead to
granuloma formation and become life threatening in severe cases
Diagnosis
Routine diagnosis is finding microfilariae in
blood smear, X-ray or ultrasound and
immunodiagnostic (ELISA)
 Dogs and other susceptible animals should
be given prophylactic doses of Ivermectin or
Milbemycin once a month or DEC once each
day, these drugs do not affect adults, which
must be killed with other drugs
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Diagnosis cont.
Microfilariae in blood
Heartworm can affect humans
through mosquito bites. This
X-Ray image of a person with
heartworm was in a human
medical journal
Microfilaria picture
Treatment and prevention
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Surgery to remove worms
To treat Microfilaria we can use
Chemoprophylaxis drugs such as
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Macrocyclic lactones
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Ivermectin (Heartgard)
Milbemycin oxime (Interceptor)
Moxidectin (ProHeart)
Selamectin (Revolution)
Diethycarnamazine Citrate (DCE)—
(Filaribits)
(None of microfilaricides are approved
by FDA but licensed veterinarians are
permitted to use it)
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Treatment & Prevention cont.
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For adulticide therapy
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Melarsomine Dihydrochloride
(Immiticide)
For Larvae therapy
Ivermectin in combination
with pyrantel pamoate—this
prevents development and
infection of larvae
Treatment should be
sequential—adult,
microfilaria, and
precardiac larvae
Treatment controversy
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Most heartworm drugs are not FDA approved
yet are sold over-the-counter
Veterinarians can use “extra labels” i.e. design
treatment procedure that individual vet thinks
is right. Sometimes preventive treatments are
given to dogs without testing for presence of
adult worms.
Even if dogs with patent infection are given
microfilaria treatment, most remain being
microfilaremic for as long as a year
Question #6
In the article you read, what was
mentioned as a solution for this
problem?
 Verifying if dogs are heartworm negative
 If they are infected, treat them with
Immiticide to kill the adult heartworms
and start the macrocyclic lactones
 Stop over-the-counter sale
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Public Health Concerns
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It can cause death in highly infected dogs
Direct cost to pet owners providing treatment
Heartworm dies shortly after arriving in the
human lung and form granuloma which might
look like lung cancer during X-ray exam.
The only medical consequence they might
have is misdiagnosis of granuloma in lungs for
lung cancer.
It was believed heartworm infected the human
eye but was found being caused by closely
related parasite of raccoons Dirofilaria tenuis.
Control
Pet owners should provided
chemoprophylaxis during mosquito
season
 Mosquito control in residential areas
 Treating dogs with antibiotics to make
sure there is no more production of
microfilariae.
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Reference
http://cal.vet.upenn.edu/dxendopar/parasitep
ages/filariidsandspirurids/d_immitis.html#life
cycle
 http://www.heartwormsociety.org/MediaLette
r.htm
 http://en.wikipedia.org/wiki/Wolbachia
 http://ucdnema.ucdavis.edu/imagemap/nem
ap/ENT156HTML/nemas/dirofilariaimmitis
 Schmidt, G. and Robert, L. Foundations of
Parasitology. 7th edition
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