Series of Presentations on Nematodes from Veterinary Parasitology By Urquhart, Jenning

1. Superfamily Filaroidea
This superfamily is closely related to the spiruroidea
because all of its genera have indirect life cycle.
None of them inhabit the alimentary tract and they depend
on insect vector for transmission.
Within the superfamily, the differences in biological behavior
are seen.
The more primitive forms laying eggs which are available to
vectors in dermal exudates.
The more highly evolved forms laying larvae termed
microfilariae which are available to the insect vectors in the
blood and tissue fluids.
In some species, the microfilariae only appear in the
peripheral blood and tissues at regular intervals, some
appearing in the day time and others at night; this behaviour
is termed diurnal or nocturnal periodicity.

2. –Dirofilaria immitis (HEARTWORM)
Definitive Host Spectrum
• Dogs – primary definitive host
• Cats
• humans
• Also reported in horses, bears
Intermediate Host
• Mosquitoes (many species depending on geographic
location)
Geographic Distribution
• Most tropical, subtropical and warm temperate areas of
the world

3. Morphology
– Adults - long, slender, white;
males 12-16 cm, females 25-30
cm; posterior of male with a
corkscrew tail;
– Microfilariae - 290-330 microns
long, 6-7 microns wide; tapered
anterior end, posterior end
straight; no cephalic hook; not
ensheathed; survive in a dog's
circulation up to 2 years

4. Life Cycle (Stages)
• Microfilariae are ingested by mosquitoes during a blood meal
– Development from mf to infective L 3 occurs in the stomach,
and takes 10-14 days
– As the IH feeds, the L 3 enter through the puncture wound
– Molt to L 4 occurs at 0-10 days post infection (dpi)
– L 4 migrate to muscle and become dormant to 60 dpi (at this
point, they are non-allergenic)
• Molt to L 5 by 60 dpi

5. – L 5 migrate through venule walls by 70 dpi and are carried
through the right heart to pulmonary arterioles; most arrive
by 3 - 4 months post-infection; allergenic and cause
eosinophilia at approximately 60 dpi
– L 5 mature to adults with migration to right ventricle and
pulmonary trunk; one adult can produce mff after
approximately 6 months dpi and can continue for 5-7 years;
mff can survive 2 years in the circulation
– Prepatent period - 6 to 7 months
– Transplacental transmission of microfilariae has been
reported
Sites of Infection
• Right ventricle, pulmonary arteries - adults
• Submuscular membranes, subcutaneous tissues - larvae
• Blood - microfilariae

6. Pathogenesis/Clinical Signs
– Microfilariae and L5 are allergenic and will cause
eosinophilia when present
– Often chronically debilitating, primarily due to
cardiopulmonary involvement
• Roughening of endocardium and endothelium
• Valvular interference
• Pulmonary arterial hypertrophy (PAH)
• Right ventricular enlargement
• Cardiac congestion

7. Diagnosis
– Dogs:
» Clinical signs, e.g., dyspnea, decreased exercise
tolerance
» Thoracic radiography
» PAH, RVH (right ventricular enlargement)
» Thickening of pulmonary arterioles with "pruning"
(abrupt loss of arteriolar branching)
• Eosinophilia in all cases
• Serologic testing for amicrofilaremic infections when
clinical signs suggest heartworm or for research subjects

8. Cats:
» Clinical signs less specific than in dogs, e.g.,
coughing, vomiting - asthma,
» Thoracic radiography
» Right side enlargement
» Pulmonary arterial enlargement
» Microfilariae - use same techniques, but mf are
detected in only about 20% of infected cats
» Eosinophilia - seen in only about one third of
infected cats
» Serologic testing

9. Treatment
» Adulticides (for otherwise healthy patients)
» Melarsomine dichloride 2 injections I.M. 24 hours
apart
» Thiacetarsamide sodium, given IV b.i.d. for 2 days;
restricted activity (no running) for 3-6 wks
» Microfilaricides
» Ivermectin
» Milbemycin
» Prophylaxis (only when patient is mf negative)
» Diethylcarbamazine, given p.o. daily during the
mosquito season and for 2 months after, recheck
yearly - effective against molting larvae
» Ivermectin, given once a month, recheck at least
yearly - effective against L4

10. » If mf persist following adulticide, consider failure of
the adulticide
» Aspirin - supportive therapy during adulticide
therapy
Other Control Measures
Keep dogs indoors during peak mosquito-biting
hours
Public Health Significance
» At least 100 human cases in the US have been
reported
» Usually seen on chest radiograph and mistaken for
carcinoma of the lung
» Lung biopsy reveals heartworm

11. Dipetalonema reconditum
Definitive Host Spectrum
– Canids
Intermediate Host (Vector)
– Fleas - Ctenocephalides , Pulex), ticks (Rhipicephalus
sanguineus), lice (Linognathus)
Geographic Distribution
– US, Africa, Italy
Morphology
– Adults - males average 13 mm, females 23 mm in length
– Microfilariae - 250-275 microns long, 4-4.5 microns wide;
blunt (same diameter throughout) anterior end, cephalic
hook; not ensheathed

12. Life Cycle (Stages)
– Microfilariae are ingested by IH during a blood meal
– Development to L 3 takes 7-19 days
– Mode of entry into the DH is not definitely known - perhaps
the infected flea is bitten by the dog, L 3 are released and
penetrate the mucous membranes of the mouth
– Prepatent period - 61 to 68 days
Pathogenesis/Clinical Signs
They are not especially pathogenic except for causing
occasional cutaneous ulceration and subcutaneous
abcesses.

13. Diagnosis
– Usually fewer in number than Dirofilaria mf
Treatment - None Approved
– Microfilaricides
– Ivermectin (0.25 mg/kg)
– Milbemycin
Other Control Measures
– Flea, louse, tick control
Public Health Significance
– None known

14. Onchocerca volvulus (NODULAR WORM OF MAN)
Definitive Host Spectrum
– Man
Intermediate Hosts
– Blackflies - Simulium spp.
Morphology
– Adults - filariform, male posterior end coiled; males
19-72 mm long, females 33-50 mm long
– Microfilaria - not sheathed, two sizes: large are 285-
370 microns, small are 150-287 microns
Life Cycle (Stages)
– Mf produced in dermis, may be found in peripheral
blood
– Simulium serve as IH with L 1 -L 3 present
– L 3 introduced into or onto skin
– Prepatent period - about 1 year

15. Sites of Infection
– Adults may be found where bones are near the skin surface
– Dermis
– Eyes
Pathogenesis/Clinical Signs
– In Africa, larval migration into eyes = "river-blindness"
– In Americas, skin nodules
– Eosinophilic granulomas
Diagnosis
– Microfilaria, Blindness in endemic areas, Nodules; biopsy
Treatment
– Ivermectin, For nodules, surgical removal
– Other Control Measures
– Attempt, usually unsuccessful, at vector eradication

16. Wuchereria bancrofti
– Important species
• Wuchereria bancrofti
• W. pacifica - may be a separate species or a geographic
strain
• Definitive Host Spectrum
– Humans
• Intermediate Hosts
– Larvae in mosquitoes (specific for geographic area)
• Geographic Distribution
• Tropical area

17. • Morphology
– Adults - anterior end enlarged and rounded, with neck;
mouth circular without lips; cuticle smooth; male posterior
end curved sharply with narrow caudal alae, spicules very
unequal, 40 mm x 100 microns; females up to 100 mm x 300
microns
– Microfilariae - sheathed, 250 to 300 microns long x 7.5 to 10
microns wide
Life cycle
– Adults in lymph nodes
– Microfilariae in blood; nocturnal periodicity for W. bancrofti ;
nonperiodic, day and night for W. pacifica
– Prepatent period - up to 10 months
Sites of Infection
• Lymph nodes - adults
• Lymphatic circulation, peripheral blood circulation -
microfilariae

18. • Pathogenesis/Clinical Signs
– W. bancrofti one of classic causes of elephantiasis in
humans
• The result of a long term or chronic infection
• Lymphadenitis initially due to occlusion of lymph vessels
• Retrograde tissue edema
• Urticaria and eosinophilia allergic responses
• Death and disintegration of adults produce macrophage
invasion, giant cell formation, fibrosis
• Legs, arms, other appendages enlarge
– Secondary bacterial infections
– Microfilaremia may result in synovitis, glomerulonephritis

19. • Diagnosis
– Microfilariae
– Clinical signs in endemic areas
• Treatment
– Diethylcarbamazine drug of choice for adults and
microfilariae, but with complications, i.e., allergic
– Ivermectin potential prophylaxis
– Physical therapy to reduce symptoms
• Other Control Measures
– Elimination of vector breeding areas
• Public Health Significance
• Usually chronic; may be life-threatening

20. Setaria spp. (Abdominal worms)
• Definitive Host Spectrum
– Domestic and wild ruminants, equids
• Intermediate host
– Mosquitoes (Aedes, Culex, Anopheles), horn flies
(Haematobia irritans)
• Geographic Distribution
– Worldwide
• Morphology
– Adults - long, slender, white; males up to 10 cm,
females up to 13 cm; males have a corkscrew tail
– Microfilariae - ensheathed; those in ruminants 240-
260 microns, those in equids 190-256 microns

21. Life Cycle (Stages)
– Microfilariae are picked up by IH during a blood meal
– Larvae are known to develop in thoracic muscles of
mosquitoes and become infective L 3 in 12-16 days
– Infection/migration pattern are not definitely known
– Prenatal infection has been recorded
– Prepatent period - 8 to 10 months
• Sites of Infection
– Peritoneal cavity or surfaces; occasionally pleural cavity,
scrotum - adults
– CNS, eye - ectopic (L 4 )
– Blood - mf

22. Pathogenesis/Clinical Signs
– Usually nonpathogenic in the peritoneal cavity, but
peritonitis is possible
– CNS infection in horses is called "kumri"
– In CNS lesions more eosinophils than do bacterial or
viral infections
• Diagnosis
– Use a concentration technique to find mf in blood -
they are usually low in numbers
• CNS infections of L 4 or immature L

23. • Treatment
– Moxidectin
– Ivermectin (0.2-0.5 mg/kg was 80-88% effective in
horses)
• Other Control Measures
– Attempt to control vectors with insecticides or
repellents, e.g. ear tags, dust bags, back rubbers, for
ruminants
• Public Health Significance
– None known