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Annual condemnation of livers of 3-4% of US cattle (25% Louisiana) at $3-5 each due to parasites.
Determinants: Neutral, well buffered soils (Ca++) in alluvial river basins, prairies and coastal marshes that support Lymnaea intermediate hosts, a ‘ mud snail’ that occurs in well-oxygenated shallow water bodies that periodically freshen with rains. In western states, habitats are typically springs, sloughs or seeps in coastal and mountainous zones.
50o F (10o C) is the ‘base temperature’ required for progression of both the Lymnaea life cycle and the development of free living stages in the environment. Optimum development occurs at 18o C
10 days at 25 C
115 days at 10 C
Encyst in hours
Total time free living stages: 2 to 5 months
Asexual reproduction sporocysts, rediae takes 42 days at 25 C, 115 days at 15 C
Lives 24 hr
Metacercariae excyst in the duodenum and penetrate via the peritoneum into the liver parenchyma by 4-5 days. Migrating flukes leave necrotic tracts in their wake, enter bile ducts after 6-8 weeks and grow rapidly to adult egg shedding flukes by 8-10 weeks. Maximum egg shedding is at 14-20 weeks. Fasciola is most pathogenic at entry to bile ducts, and in the rapid growth and early egg shedding phase <6 months after major infection.
Typical habitat in alluvial Red River Basin. Habitats are shallow depressions (eg. imperfections in ‘ditch and crown’ drainage systems seen here) that stay wet half the year and freshen with each rain. Lymnaeid snail hosts are found on mud at the edge of habitats. Rain stimulates shedding of cercariae by snails, a dispersal adaptation that helps spread infection to a larger area of the pasture. Most infections are focal, in and around snail habitats.
Snails grow to about 1cm in length
Eggs persist in dung pat reservoirs on pasture, must be washed free of feces into water phase to develop further into miracidia.
Eggs are large, operculated and golden in color
Fasciola is diagnosed by fecal sedimentation examination
Miracidiaare stimulated to hatch from eggs by light after at least 10 days development
Lymnaeid snails have a dextral spiral shell whorl (‘right-handed’) and ‘cat ear’ antennae
Asexual Multiplication in snail hosts result in a sporocyst and two rediae generations. Rediae produce cercariae. One miracidium can lead to several hundred cercariae
Metacercariae have a resistant 4-layer cyst wall and survive months in wet, cold conditions. A 2 week sustained summer drought kills metacercariae and forces estivation of snail populations, thus ending the transmission season
Fluke with Spines of flukes in bile ducts erode proliferated epithelium and consume blood and exudate. Proline, a by-product of the incomplete metabolism of Fasciola, rises to 1000 times normal. Proline excess has been shown to lead to bile duct fibrosis and depression anemia experimentally. Fasciola consumes only 0.2 ml blood/fluke/day, not enough for the anemia, hypoproteinemia seen with heavy fluke infections.
Heavily Parasitized Heifer
Subacute clinical infections are seldom seen in cattle, associated with burdens of >200 flukes. Chronic sub-clinical disease is typical. Most fluke effects occur 6-20 weeks after heavy exposure (after entry to bile ducts), then lessen. An 8-28% reduction in rate of gain has been reported in feeder calves infected with 40-140 flukes. Minor effects with <10 flukes.
Sheep with bottle jaw
Sheep and Goats: High mortality outbreaks can occur. Acute disease occurs at bile duct entry of massive (>5000 metacercariae) numbers of flukes. Sub-acute and chronic clinical disease is due to burdens of >800 and >200 adults in bile ducts, respectively.
Liver infarct, Bacillary Hemoglobinuria
Bacillary hemoglobinuria is predisposed by fluke migration anaerobic tracts. In some geographic areas of the west, vaccination of cattle must be given each 6 months where soils favor persistence of Clostridium hemolyticum. Cl. Novyi causes ‘Black disease’ in sheep, and rarely cattle, with multifocal lesions. Anaerobic bacteria proliferate in necrotic tracts and produce potent exotoxins and acute death.
Seasonal TransmissionDiagram of the Gulf Coast Region based on 5 years’ experimental data – Late winter, spring transmission
100-fold annual variation in fluke transmission and risk of economic losses at a farm near Alexandria, LA, with corresponding spring and fall climate forecast indices.
- Maximum/Minimum Temperatures C
- Growing degree days (Base 10o C) and soil moisture water budget.
- Accumulate (add) GDD if water in top 1” of soil
- Surplus water (run-off) times GDD on rain days
ACCUMULATES DAILY LIFE CYCLE INDEX
**Risk increases exponentially with index due to the ‘multiplier effect’ of the asexual reproduction phase in snail hosts. This makes possible the well known explosive nature of fluke outbreaks.
Fasciola climate forecast regional risk index map for Louisiana and Texas in an average year (based on 30 year average climate data)
Individual farm risk is related to the % area occupied by snail habitat and stocking rate. Farms with over 5% habitat area are very high risk premises. This is a ‘low-lying’ high risk cow-calf operation in coastal Louisiana.
Individual farm risk also can vary by 100 fold in the same area, based on drainage characteristics of soil texture classes (eg. sand loam, loam, clay loam, clay, hydric clay). White lines indicate farm boundaries overlayed on USDA soil type map.
Bile duct Bile duct Parenchyma Drug AdultsImmatureMigratory
Hexachloroethane* 90% ? -
Albendazole 10mg/kg 75-90% 33% -
Clorsulon 7mg/kg >99% 96% -
in Ivomec+ 2mg/kg >90% >70% -
Triclabendazole >99% >99% >90% (10mg/kg,available worldwide, not USA)
*Removed from market as a carcinogen in 1985
Southern USA pattern
Western US Pattern
Interpretation% PrevalenceMean EP2G
Low burden < 25 % < 1
(No economic losses)
Moderate Burden 25-75% 1-3
(Economic Loss Possible)
Heavy Burden 75-90% 3-10
(Economic loss probable)
Economical >90% >10
-Fasciola must be differentiated from Paramphistomum, a non- pathogenic rumen fluke that is smaller, greyish in color
-Examine 10 cows
Several immunodiagnositic tests have been developed for Fasciola, including a serum ELISA and one based on detection of coproantigen in feces. Some are used in Europe, but are not yet commercially accepted in the USA.
Fasciola gigantica vs F hepatica
F. gigantica is the tropical-sub-tropical counterpart of F. hepatica. It is 2-3 times larger, somewhat more pathogenic, and has a longer prepatent period (10-12 weeks). Lymnaeid vector spp are more aquatic, inhabiting permanent bodies of water, irrigation canals and seasonal flood areas.
Deer are normal hosts, cattle and sheep incidental hosts
Fascioloides magna ininfected deer liver. Note the mild inflammatory response of deer, the normal host.
Note the large size of F. magna and the black lymph nodes and streaks of pigment in this cattle liver due to regurgitated fluke ingesta.
Deer liver heavily infected with F magna. Heavy burdens are well tolerated by deer and pathological reaction is mild due to a well adapted host-parasite relationship. The life cycle is similar to F hepatica, but has a wider geographic distribution associated with the wider variety of snail hosts, some in more aquatic habitats. Flukes are found in parenchyma cysts with a fistulous communication to bile ducts for escape of eggs.
Cattle liver with F magna. Note the more intense pathological reaction, with calcification and dark pigmentation caused by flukes in liver parenchyma cysts. Diagnosis is made in cattle mainly at slaughter inspection because communication of cysts with the bile ducts is walled off by inflammation, preventing egg shedding. Little economic damage is associated with F magna in cattle, except in some parts of the country with heavy infections acquired on ranges shared with abundant deer (eg Texas hunting clubs). In LA, 2% of livers condemned have F magna.
In sheep, F magna is not walled off and flukes continue to migrate with ultimate destruction of the liver parenchyma. One or two flukes can kill sheep and this parasites effectively limits sheep production in parts of the great lakes region and other areas where ranges must be shared with deer populations.
Rumen fluke in situ among rumen papillae. Note the conical shape and attachment by a posterior sucker, an adaptation of the ventral sucker
The posterior sucker of a paramphistome attached to rumen epithelium. The rumen fluke is not considered to be pathogenic in the USA, although massive infection (>30,000) by tropical species may cause severe, fatal disease due to duodenitis caused by the larva migration phase of the life cycle in the duodenum mucosa. The life cycle and transmission on forage is similar to F hepatica.
Paramphistome eggsare greyish, more pointed at the operculum end and slightly smaller, features which allow differentiation from Fasciola at fecal sedimentation examination. Paramphistomes are often found in the same herds as Fasciola and in the Southeast are transmitted by the same snail. Since they are not affected by available flukecides, they can be counted and used as a surrogate indicator of how severe Fasciola would be without benefit of control programs.
Dicrocoelium Adult fluke
Dicrocoelium eggs are small in size and contain a fully developed miracidium
Dicrocoelium land snail host shedding eggs in ‘slime balls’
Black ant second intermediate host consuming snail slime containing cercariae
Dicrocoeliummetacercariae encyst in brain tissues of ants, causing ‘acrophilia’ a behavioral disturbance that induces them to climb high on vegetation, clamp down with pincers during cool of night, and so become more available to early grazing animals. Distribution is limited to central New York and areas of Pennsylvania, New England , Quebec, British Columbia by the distribution of the snail and ant hosts. It is common in Europe and Asia.
“Crazy ant” on flower.