Liver Fluke in Goats |
Goat Parasite Information and Control | |||||
Written by Administrator-GL | |||||
Wednesday, 01 August 2007 | |||||
Page 1 of 3 LIVER FLUKE(Fasciola hepatica) Understand the danger of Liver Fluke in goats and the damage it does!1Adult Liver Fluke Read our Article on effective deworming Liver Fluke is spread by snails and slugs, so anywhere you have snails or slugs you probably have liver fluke. The goats ingest grass with an encysted stage of the fluke present. After the goats eat this contaminated grass, the juvenile flukes "burrow" through the lining of the intestine, escape into the peritoneal cavity (the inside of the abdomen) and migrate to the liver. The flukes bore their way into the liver and over the next 6 weeks or more make their way to the interior of the liver and finally arrive in the bile ducts where they begin to lay eggs. The fluke eggs are shed into the manure of the goats. These eggs hatch and make their way to fresh water snails, which they infect and undergo additional development. They eventually emerge from the snail as young flukes and encyst (form a resistant coating) on blades of grass. When goats ingest them, the life cycle can be completed. What damage do flukes cause? The young flukes cause quite a lot of damage as they migrate through the liver. If only a few flukes are migrating through the liver at one time, the damage to the goat is minimal. However, if many flukes are migrating at the same time, the damage to the liver can be extensive. In these cases, diarrhea, weight loss, and jaundice (yellow mucous membranes) can be observed. In addition to the direct damage to the liver, there is another problem liver flukes can precipitate and that is Redwater. Each fluke can cause the loss of 0.5ml of blood per day from the liver. A moderate infestation in cattle of 100-200 fluke can lead to blood loss of up to half a litre each week, so often infected animals can be anemic. Redwater (Bacillary Hemoglobinuria) can affect goats at any time of the year; however, it is most common in the late spring, summer, and autumn. Redwater is caused by a bacterium called Clostridium hemolyticum, which colonizes in the liver of susceptible cattle and produces protein toxins that in turn destroy the body's red blood cells, damages other organ systems and rapidly causes death. The migrating flukes damage local areas in the liver causing low oxygen tension and the bacteria prefer these conditions and begin to grow rapidly in these damaged areas. The disease has a short incubation period and the vast majority of affected goats are usually found dead and bloated. Which drugs are effective against liver flukes? Currently, there are only two drugs available that are effective against liver flukes in cattle. Both work best against the adult flukes, but there is some effect on the migrating juvenile flukes. Clorsulon is effective only against liver flukes and it is sold alone as Curatrem® or in combination with ivermectin as Ivomec® Plus. Thus, Curatrem® can be used to kill the flukes or Ivomec® Plus can be used to kill the flukes plus the internal parasites (worms) and external parasites (sucking lice). Additionally, albendazole (Valbazen®) has activity against flukes and internal parasites. All the drugs and combinations of drugs have advantages and disadvantages in terms of cost, ease of administration, withdrawal times, and effectiveness. Consult with your veterinarian to be certain which product will work best for your operation. Also, review with your veterinarian the time of year that will be most cost-effective for administration of drugs to kill flukes. Another problem liver flukes seem to be associated with is decreased fertility. Studies have been published that show decreased pregnancy rates in replacement heifers and increased age to puberty in heifers infected with liver flukes. Thus, flukes can cause losses in a number of ways: (1) direct damage to the liver, with weight loss and diarrhea, (2) death loss due to Redwater secondary to liver damage of migrating flukes, and (3) decreased reproductive performance. How common is Redwater? The disease is common in the western United States and the first cases were reported in California in 1916. Most areas of California are at risk for this disease. It is most common in areas with alkaline soils, water with a pH of 8, and in pastures that are not well drained. The agent is often present in the feces of normal cattle and has been isolated from the liver and kidneys of healthy cattle. Redwater is uncommon in cattle less than one year of age. The most commonly affected cattle are adults in good condition. The disease has a very short incubation period and the vast majority of affected cattle are usually found dead and bloated. If clinical signs are observed, the most common ones are anemia, rapid breathing, high fever (104-106°F), and urine that is dark red and foamy in appearance. The red urine is due to the presence of large amounts of hemoglobin from the destroyed red blood cells. The affected animals are weak, depressed and usually die within 12 hours of the time the first signs appear. Treatment is almost always unsuccessful even if the animals are seen prior to death. The course of the disease is very rapid and most all cattle with Redwater are simply found dead and most bloat soon after death. Other conditions that can be confused with Redwater include (a) Leptospirosis, (b) legume bloat, (c) copper toxicity, (d) anaplasmosis, (e) anthrax, (f) bracken fern toxicity, and (g) blackleg. Therefore, animals that die suddenly should be examined by your veterinarian or sent to the diagnostic laboratory to determine the cause of death so that other losses can be prevented. Your veterinarian can easily identify Redwater as the cause of death and can take impression smears of the liver to confirm the condition. Life cycle of liver fluke The life cycle of the liver fluke is very complicated. A simplified version is shown below: 1. The adult liver fluke in the liver of its host produces eggs which pass onto the pasture 2. These eggs hatch in warm damp conditions to produce mobile larvae (miracidia) which then infect a particular species of snail 3. The larvae multiply within in the snail and develop into another swimming stage (cercaria), which emerge from the snail and settle on the pasture 4. These then develop into a highly tolerant non-mobile stage (metacercaria) that can survive for at least a year. Once eaten by the goat these hatch and migrate to the liver. Fluke eggs do not develop significantly or hatch below 50degrees F – therefore the lifecycle of the liver fluke is mainly completed between May and October. Liver Fluke egg Looks very similar to the Haemonchus contortus egg Although snails often carry infection throughout the year, two main peaks of snail infection are recognize, (summer infection and winter infection) the timing of which is dependent on climatic conditions 8. Summer infection – snails become infected with miracidia in late spring/early summer; either from fluke eggs deposited by grazing animals in spring, or from those deposited on the pasture the previous autumn/winter. This eventually can lead to clinical disease early/mid winter. Winter infection – As the snails become inactive during winter the development and shedding of the miracidia can no longer be completed, so they remain dormant within the snail until the following spring. This winter infection acts as a reservoir of infection for the following year. Acute fasciolosis: late autumn/early winter Sub acute fasciolosis: late autumn to spring Chronic fasciolosis: winter and spring Each adult fluke can be up to 3cm long. Adult liver fluke can survive in goats from six months to two years. Larval development in the snail is dependent on temperature (and rainfall); from 20 days at 30oC to 80 days at 15oC. The complete cycle of this fluke takes 3 –4 months in ideal conditions. Antemortem findings : 1. Weight loss and emaciation 2. Fall in milk production 3. Anemia 4. Chronic diarrhea 5. Swelling in the mandibular area Postmortem findings : 1. Emaciated, anemic or edematous carcass in severe chronic infestations 2. Presence of flukes in enlarged and thickened bile ducts and in the liver parenchyma 3. Hepatic abscesses and secondary bacterial infection 4. Calcification of bile ducts 5. Black parasitic material (excrement) in the liver, lungs, diaphragm and peritoneum 6. Black lymph nodes of the lungs and liver due to fluke excrement 7. Icterus due to liver damage Numerous flukes of Fasciola hepatica observed in the bile ducts and liver parenchyma ( internal anatomy of the liver) of a cow: 1 1 Fasciola hepatica-Liver Fluke. Normal sheep liver on right, and liver damaged by migrating larvae on left. This photo shows Chronic Liver Disease caused by Liver Fluke: 1 1Photos courtesy of FAO Animal Production and Health Papers
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Last Updated ( Thursday, 17 November 2011 ) |
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