NAVLE Multisystemic

Camelidae and Cervidae Multisystemic Internal Parasites – NAVLE Study Guide

📅 March 28, 2026 ⏱ 25 min read 👁 2 views

Multisystemic internal parasites in camelids and cervids represent a critical category on the NAVLE. These parasites cause disease affecting multiple organ systems including the liver, GI tract, CNS, and cardiovascular system.

Overview and Clinical Importance

The concepts of definitive hosts, dead-end hosts, and aberrant hosts are particularly important for liver flukes and meningeal worms. Camelids often respond differently than domestic ruminants to the same parasites.

Category	Findings
Clinical Signs	Reduced appetite, weakness, recumbency, anemia, weight loss, ill-thrift, sudden death (acute)
Diagnostic Methods	SEDIMENTATION (not flotation) for fecal eggs; ELISA most sensitive; Liver enzymes elevated (GGT, AST)
Necropsy Findings	Enlarged liver with migratory tracts, thickened bile ducts, biliary hyperplasia, granulomatous hepatitis with ova

Section 1: Liver Flukes (Trematodes)

1.1 Fasciola hepatica (Common Liver Fluke)

Etiology and Life Cycle

Fasciola hepatica is a large trematode (up to 30mm x 13mm) parasitizing bile ducts. The indirect life cycle requires a lymnaeid freshwater snail intermediate host (Galba truncatula). Eggs pass in feces, embryonate in water, hatch as miracidia, penetrate snails, develop through sporocyst/rediae/cercariae stages, then encyst as metacercariae on aquatic vegetation. Hosts are infected by ingesting contaminated plants.

Host Response in Camelids

Camelids respond to F. hepatica similarly to SHEEP rather than cattle, making them highly susceptible. Their bile duct anatomy resembles equines more than ruminants. Clinical disease includes acute, chronic, and fatal forms. Infections with Dicrocoelium dendriticum are even more severe in camelids than in other species.

Clinical Signs and Diagnosis

High-YieldStandard fecal FLOTATION will NOT detect liver fluke eggs. Always use SEDIMENTATION for Fasciola diagnosis. ELISA is more sensitive than fecal examination, especially early in infection.

Treatment Options

1.2 Fascioloides magna (Giant Liver Fluke/Deer Fluke)

Host Classifications - CRITICAL FOR NAVLE

Fascioloides magna is North America's largest liver fluke (up to 10cm x 3.5cm). Understanding host classifications is essential:

NAVLE TipHOST CLASSIFICATION mnemonic: 'Deer Define, Cattle are Dead-ends, Sheep are Aberrant.' In ABERRANT hosts (sheep/goats), flukes wander aimlessly = 'A' for Aimless and Always fatal!

1.3 Dicrocoelium dendriticum (Lancet Fluke)

D. dendriticum causes MORE SEVERE disease in camelids than in domestic ruminants. Unique life cycle requires TWO intermediate hosts: a land snail then an ant (Formica spp.). Metacercariae encyst in the ant's brain, causing abnormal behavior - ants climb grass tips where they're ingested by grazing animals. Camelids frequently DIE from dicrocoeliasis.

High-YieldRemember the 'Two-Host Two-Ant' rule: D. dendriticum needs TWO intermediate hosts (snail + ant), and ants behave abnormally. Camelids are extremely sensitive - 'D for Deadly in camelids!'

Drug	Dose (Camelids)	Notes
Triclabendazole	10-12 mg/kg PO	Drug of choice - effective against ALL life stages; Off-label
Clorsulon	7 mg/kg PO or SC	Adult flukes only; Available in Ivomec Plus
Albendazole	15-20 mg/kg PO	Less effective; AVOID in pregnant animals (teratogenic)

Section 2: Meningeal Worm (Parelaphostrongylus tenuis)

2.1 Etiology and Life Cycle

Parelaphostrongylus tenuis (meningeal worm, brain worm) causes cerebrospinal nematodiasis in camelids. White-tailed deer are the DEFINITIVE HOST (up to 80% infected in endemic areas) and carry the parasite asymptomatically. Terrestrial gastropods (snails/slugs) are intermediate hosts. Camelids become infected by accidentally ingesting infected gastropods while grazing.

2.2 Clinical Signs in Camelids

NAVLE TipNAVLE trigger: 'Camelid + Hindlimb ataxia + Fall/Winter + White-tailed deer area = Think P. tenuis FIRST!' Hindlimbs affected before forelimbs; animals stay bright and alert (unlike rabies or listeriosis).

Diagnosis

NO COMMERCIAL ANTEMORTEM TEST EXISTS. Presumptive diagnosis: (1) Compatible clinical signs, (2) Exposure to white-tailed deer habitat, (3) CSF EOSINOPHILIC PLEOCYTOSIS with elevated protein, (4) Rule out other neurological diseases. Fecal examination is NOT useful (non-patent in camelids).

Treatment

High-YieldPrognosis is GUARDED to POOR for moderate-severe signs. Treatment expensive and often unrewarding. AVOID corticosteroids - associated with worse outcomes in studies!

Prevention - 'DEFEND' Mnemonic

D = Deer exclusion (fencing, reduce population)

E = Eliminate snail/slug habitats (drain wet areas)

F = Fence with rock barriers + molluscicides

E = Employ guardian dogs

N = Never co-graze with deer

D = Deworm strategically (use with caution for resistance)

Host Type	Species	Outcome
Definitive Host	White-tailed deer, Elk, Caribou, Mule deer	Flukes in thin-walled cysts with bile duct connection; Patent infection; Minimal disease
Dead-End Host	Cattle, Moose, Bison, LLAMAS, Pigs, Horses	Thick-walled cyst encapsulation; Rarely produce eggs; Moderate damage, usually tolerated
Aberrant Host	SHEEP, GOATS, Bighorn sheep, Roe deer	CANNOT encapsulate flukes; Continuous aimless migration; Severe hemorrhage; OFTEN FATAL

Section 3: Haemonchus contortus (Barber Pole Worm)

Haemonchus contortus is the most important blood-feeding nematode of camelids. Each worm consumes up to 0.05 mL blood/day. With 5,000 worms, a camelid loses 250 mL blood daily! Females produce 5,000-15,000 eggs/day. The 'barber pole' appearance = white ovaries coiled around blood-filled intestine.

3.1 Clinical Signs and Diagnosis

High-YieldFAMACHA scoring is VALIDATED for camelids! Key: Haemonchus causes ANEMIA WITHOUT DIARRHEA. Alpaca with pale conjunctivae + bottle jaw + NO diarrhea = Think Haemonchus first!

3.2 Anthelmintic Resistance Crisis

Studies on southeastern U.S. camelid farms found ALARMING resistance rates:

Benzimidazoles (fenbendazole, albendazole): 100% farms with resistance
Ivermectin: 88-97% farms with resistance
Levamisole: 22% farms with resistance
Moxidectin: 22% farms with resistance

Treatment Recommendations

NAVLE TipPOUR-ON formulations are INEFFECTIVE in camelids due to unique skin/fiber characteristics = extremely low drug bioavailability. Always use ORAL formulations! For resistance testing, use FECRT - recheck FEC 14 days post-treatment.

System	Clinical Signs
Neurological (Classic)	HINDLIMB ataxia (wide-based stance), hindlimb weakness progressing to recumbency, head tilt, circling, neck arching, proprioceptive deficits
General	Weight loss, difficulty rising, lethargy; Animals remain BRIGHT and ALERT with good appetite until late stages
Temporal Pattern	Most cases October-March (fall/winter); Clinical signs 45-53 days post-infection; Onset may be gradual or sudden

Section 4: Eimeria macusaniensis (Big Mac Coccidiosis)

Eimeria macusaniensis ('E. mac' or 'Big Mac') is the MOST PATHOGENIC coccidian of South American camelids. Unlike other coccidia that primarily affect young animals, E. mac causes severe disease in camelids of ALL AGES, including adults.

4.1 Distinguishing Features

4.2 Clinical Presentation

GI signs: Colic, decreased appetite, weight loss; Diarrhea may or may NOT be present
Protein loss: Hypoproteinemia, hypoalbuminemia, dependent edema
Shock: Circulatory collapse, pale membranes
Secondary infections: Clostridium perfringens enterotoxemia commonly associated
SUDDEN DEATH: Common presentation - may be first sign!

High-YieldE. mac is the ONLY coccidia that routinely kills ADULT camelids. Clinical signs may precede positive fecal results (long prepatent period). Sudden death without prior signs = E. mac enterotoxemia on your differential!

4.3 Treatment

Drug	Protocol	Notes
Fenbendazole	50 mg/kg PO daily x 5 days	First-line treatment; Higher dose than for GI parasites
Ivermectin	0.2-0.4 mg/kg SC	Often combined with fenbendazole
Anti-inflammatories	NSAIDs (flunixin)	Corticosteroids CONTROVERSIAL - may worsen outcome!

Section 5: Elaeophora schneideri (Arterial Worm) in Cervids

Elaeophora schneideri (arterial worm) inhabits carotid and cephalic arteries. Mule deer and black-tailed deer are normal definitive hosts (asymptomatic). Elk, moose, white-tailed deer, sheep are aberrant hosts developing elaeophorosis. Horse flies (Tabanus spp.) are vectors.

Clinical signs in aberrant hosts (elk/moose):

'Clear-eyed' blindness: Optic nerve ischemia with normal-appearing eyes
Necrosis: Sloughing of ears, muzzle, antler tips
Neurological: Ataxia, circling, incoordination
Mastication problems: Food impaction ('lumpy jaw') in white-tailed deer

High-YieldKey differential: Elk with blindness + ear tip necrosis in western U.S. = Think Elaeophora! 'Clear-eyed blindness' is characteristic - eyes appear normal but animal is blind due to optic nerve ischemia.

Parameter	Findings
Clinical Signs	Pale mucous membranes (anemia), BOTTLE JAW (submandibular edema), weakness, weight loss; Diarrhea NOT typically present
Laboratory	Low PCV/hematocrit, hypoproteinemia, hypoalbuminemia; FEC may be high but does not always correlate with burden
FAMACHA Scoring	VALIDATED for camelids; Score 1-5 based on conjunctival color; 1=pink (normal), 5=white (severe anemia); Treat animals scoring 4-5

Summary: Key Points for NAVLE

F. hepatica: Camelids respond like SHEEP; Use SEDIMENTATION; Triclabendazole is drug of choice
F. magna: Know host classifications - Deer=Definitive, Cattle/Camelids=Dead-end, Sheep=Aberrant (fatal)
D. dendriticum: Two intermediate hosts (snail + ant); MORE severe in camelids
P. tenuis: White-tailed deer=definitive; Camelids=aberrant; Hindlimb ataxia, bright/alert; CSF eosinophilia; Fenbendazole 50mg/kg x5d
Haemonchus: Anemia WITHOUT diarrhea; FAMACHA valid; Use moxidectin ORAL; Pour-ons ineffective
E. macusaniensis: Kills ADULTS; Largest oocyst; Long prepatent period; Sudden death; Ponazuril is drug of choice
Elaeophora: Mule/black-tailed deer=normal; Elk/moose=aberrant; 'Clear-eyed blindness', ear necrosis

Drug	Dose	Notes
Moxidectin (oral)	0.4 mg/kg PO	FIRST-LINE when sensitivity unknown; Use ORAL formulation (Cydectin Oral Sheep); Pour-on INEFFECTIVE in camelids!
Levamisole	8 mg/kg PO	NARROW safety margin - weigh accurately! Very bitter (causes foaming)
Closantel	10 mg/kg PO	Narrow-spectrum; Effective for Haemonchus and liver fluke

Feature	Description
Oocyst Morphology	VERY LARGE (up to 107 micrometers); Pyriform shape (watermelon seed/cut avocado); Very thick wall (8-12 micrometers); Micropylar cap present
Prepatent Period	LONG: 32-40 days (vs. 2-3 weeks for small coccidia); Clinical signs may appear BEFORE oocysts are shed
Environmental Survival	Oocysts survive up to 84 MONTHS - LONGEST of any known Eimeria!
Fecal Detection	Difficult - use SUGAR FLOTATION (not standard saline); Sheds infrequently; Centrifugation-flotation improves detection

Drug	Dose	Notes
Ponazuril	20 mg/kg PO x 3 days	DRUG OF CHOICE; Most effective; Repeat 10 days later; Coccidiocidal
Toltrazuril (Baycox)	20 mg/kg PO	Effective alternative; Two doses 10 days apart
Sulfadimethoxine	55 mg/kg day 1, then 27.5 mg/kg x 4-5 days	Coccidiostatic only; Less effective for E. mac

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Camelidae and Cervidae Multisystemic Internal Parasites &ndash; NAVLE Study Guide