Superfamily Trichinelloidea (finishing up) and Rhabditoidea

Question 1

Trichinella spp.

Answer 1

• Important zoonoses
• Consumption of raw or undercooked meats, esp. pork, bear, wild cats, foxes, horses, seals, or walruses
• Adult worms are seldom seen
• Pre-larvae are deposited NOT eggs
• Nine plus three unnamed genotypes
• Trichinella spiralis (domestic swine)
• Trichinella nativa, Trichinella nelsoni, and Trichinella pseudospiralis (seen in wildlife: mammals, birds, and reptiles)

Question 2

Trichinella spp. adults

Answer 2

• Tiny worms
• Females are 3-4 mm
• Males are ~1.5 mm

Question 3

Trichinella spp. life-cycle

Answer 3

• Larvae are ingested in raw or undercooked meats
• Larvae are released from nurse cells in the stomach
• Larvae enter the small intestine
• Adults mature and live in the small intestine (larvae to adult maturation takes place in 48 hours, that’s when the host starts to see clinical signs)
• The female sheds newborn larvae that enter the lymph or blood; can travel to heart and cause heart failure, or to the brain and cause CNS damage (females produce larvae in about 5 days)
• Newborn larvae are carried throughout the bloodstream
• Newborn larvae enter the skeletal muscle cell
• Larvae mature in the muscle
• Nurse cell-larva complex is formed
• Normal and calcified nurse cell-larvae complexes in the stomach

Question 4

Nurse cell

Answer 4

• Cyst

- Provides nutrition for the larvae

Question 5

Trichinella spp. clinical disease

Answer 5

• 1-2 days after consumption of contaminated meat
• -Nausea, diarrhea, vomiting, and abdominal pain
• 2-8 weeks after consumption of contaminated meat
• -Muscle pain, fever, swelling of the eyes, fatigue, headache, chills, itchy skin, cough, etc.

Question 6

Trichinellosis diagnosis

Answer 6

• Finding adult worms is rare
• Can find nurse cells in certain muscle groups: diaphragm, extrinsic muscles of the eye, and skeletal muscles
• Two primary methods of diagnosis: muscle press and enzymatic digestion
• -Diaphragm, masseter, and tongue are used

Question 7

Trichinellosis public health

Answer 7

• Historically ~360 cases per year (1947-1956)
• Trichinella is not a problem in commercial swine production
• The national surveillance program estimated about 14 cases per year between 2006 and 2015
• -Consumption of wild game meat, locally slaughtered pigs, and homemade sausages (esp wild boar and bear)
• -Some Trichinella species are cold adapted and freezing does not kill them
• Voluntary National Trichinae Certification Program aimed at continued efforts to eliminate trichinellosis

Question 8

Superfamily Rhabditoidea

Answer 8

Family Rhabditidae

• Free living nematodes
• Facultative parasites of domestic animals
• Patient may be susceptible if laying in a moist environment
• Rhabditis strongyloides
• -Rhabditic dermatitis in cattle, dogs, etc.
• Halicephalobus gingivalis
• -Maxillary and CNS disease in horses

Family Strongyloididae

• Intestinal “threadworms”
• Alternating free-living and parasitic generations
• Reproduce by parthenogenesis
• Free-living L3 is the infective stage
• L1 to L3 development occurs in 24-36 hours
• No fertilization is required
• Genus Strongyloides
• Strongyloides stercoralis (dogs and humans)
• Strongyloides westeri (equids)
• Strongyloides papillosus (ruminants)
• Strongyloides ransomi (swine)
• Strongyloides tumefaciens (cats - southern US)

Question 9

Genus Strongyloides

Answer 9

• Reside in the small intestine
• Tiny thread-like adults 0.5 cm in length
• Long esophagus (almost half the body)
• ONLY females are parasitic
• Diagnostic stage = larvated egg in all Strongyloides spp. except S. stercoralis (diagnostic stage is L1 in the feces)

Question 10

Strongyloides life-cycle

Answer 10

Homogonic development

• Parasitic female lays egg
• Egg develops into L1
• L1 develops into homogonic L2 (only females)
• L2 develops into infective L3
• L3 develops into parasitic adult female

Heterogonic development

• Parasitic female lays egg
• Egg develops into L1
• L1 develops into L2
• L2 develops into L3
• L3 develops into L4
• L4 develops into heterogonic free living adults (male and female)
• Adults lay eggs
• Egg develops into L1
• L1 develops into L2
• L2 can develop into infective L3
• L3 develops into parasitic adult female (does not have to develop into infective L3, can be free-living)

Question 11

Strongyloides transmission

Answer 11

• Skin penetration by infective L3
• -Pulmonary tracheal migration to small intestine
• -Prepatent period is 7-10 days
• -Somatic migration and arrested larvae in tissues
• Transmammary (most important transmission)
• -S. westeri, S. ransomi (2-4 days PPP), and S. papillosus
• Autoinfection (important)
• -S. stercoralis
• -L1-L3 within the host, reinvasion of bowel or perianal skin
• -Serious hyperinfection - can be fatal
• -Can overwhelm the body if immunocompromised
• -Zoonotic

Question 12

Strongyloides pathology

Answer 12

• Problem in young animals
• S. westeri and S. ransomi
• -Transmammary transmission
• -Problematic in broodmare farms and farrowing operations
• S. stercoralis
• -Skin penetration and autoinfection transmission
• -Problem in kennels, young dogs, or if immunocompromised
• -Hot and humid weather worsens the problem

Question 13

Strongyloides stercoralis disease

Answer 13

• Catarrhal to hemorrhagic enteritis
• Watery to blood-streaked mucoid diarrhea
• Lethargy, listlessness, and emaciation
• Skin irritation at larval penetration site
• -Heavy or chronic infections - bronchopneumonia
• Possible minor zoonotic potential
• -Strain variations (treat as if possible zoonosis, just to be safe)
• -Between human, dog, and environment

Question 14

Strongyloides stercoralis diagnosis

Answer 14

• L1 in feces
• 300-380 um long
• Rhabditiform esophagus
• Small buccal capsule
• Large genital primordium
• Straight tail
• Esophageal bulb, isthmus, and corpus present
• Preferred method = Baermann technique
• -Diagnostic stage
• –Rhabditiform larva
• –300-380 um long
• –Rhabditiform oesophagus
• -Infective stage
• –Filariform larva
• –500-600 um long
• –Filariform oesophagus filling the anterior half of the larva
• –Notched tail end

Question 15

All other Strongyloides spp. diagnosis

Answer 15

• Use fecal floatation
• Larvated egg in feces
• Small, thin-shelled, ellipsoid with bluntly rounded ends, colorless
• S. westeri: 40-52 x 32-40 um
• S. ransomi: 45-55 x 26-35 um

Question 16

Strongyloides treatment/control

Answer 16

• Ivermectin = drug of choice for all species
• S. stercoralis - ivermectin, thiabendazole, fenbendazole
• S. westeri - ivermectin, thiabendazole, oxibendazole
• S. ransomi - ivermectin, thiabendazole, doramectin, levamisole
• S. papillosus - ivermectin pour-on and doramectin (cattle); ivermectin drench (sheep)

Question 17

Strongyloides prevention and control

Answer 17

• Strict hygiene and manure removal
• Larvae need humidity to survive and reach their hosts
• -Facilities should be kept as dry as possible
• -Direct sunlight, desiccation, cleaning with steam, hot water, bleach, etc.
• -Treatment around 2 weeks prior to parturition