General Appearance / Signs
Parasitized animals can show many signs of infection depending on the parasites present. If the parasite is disrupting the digestive tract then common signs may include rough hair coat, diarrhea, depression, weight loss or reduced weight gain, anorexia, and/or being off-feed. If the parasite consumes blood, symptoms often include 1) anemia, as viewed by pale color to the gums, vulva and mucous membranes of the inner eyelideye membranes, and even 2) bottlejaws. Again symptoms may be accompanied by weight loss and/or being off feed. Laboratory diagnostic findings may include anemia, or low packed cell volume (PCV); increased fecal egg count (FEC); and loss of plasma protein.
Fecal Egg Count
The FEC is a method to evaluate the number of parasite eggs excreted per gram of feces (epg). While this is the best method for use with live animals, there are some difficulties associated with measurement, including the following:
- Egg production does not always reflect the number of worms present because different worm species lay different numbers of eggs per adult female worm.
- Eggs cannot be completely identified to species, that is, they
may be grouped in various categories but not absolutely identified.
- How long the infection has persisted, the level of host immunity and fecal
consistency may also present difficulties.
- Some methodologies used for epg determination may be less precise than others.
The FEC, specifically for Haemonchus contortus (barber pole worm), has been shown for the most part to reflect the animal’s worm burden and also serves as an indicator of seasonal changes in level of infection. Trends in FEC over time can be seen, thus reflecting the relative direction of infection. When worms other than H. contortus predominate, FEC is a less accurate predictor of adult worm burdens. It is important to know that if heavy infection occurs over one to two weeks with H. contortus, animals may lose substantial amounts of blood with few eggs in the feces as the prepatent period is about three weeks.
Many diagnostic labs will also hatch out worm eggs from fecal samples as an added paid service if requested. This allows you to identify the actual species of abdominal or intestinal worms that are parasitizing your herd.
“Drench rite tests” can also be conducted by some diagnostic labs to identify the extent of dewormer resistance exhibited by different species of worm larvae in your herd. These tests are much more expensive than regular fecal egg counts because of additional expenses and labor. More information on them can be found at http://www.acsrpc.org/Resources/doingownfecs.html
Blood Packed Cell Volume
Nematode parasites can affect an animal’s ability to maintain “erythropoesis“, the ability to make red blood cells. The PCV is the percent of the blood that is red blood cells. Normal is usually above 30 percent. When PCV drops below 20 percent, symptoms of anemia usually start to appear. PCV is determined by centrifuging blood in a capillary tube — about the size of a ballpoint pen refill — which packs the cells and measures percent. All nematode parasites can result in chronic anemia, in which red blood cells are not being made fast enough to keep up with demand. Of special note, H. contortus can lead to substantial acute blood loss and death. PCV values have been used to support other response criteria, and it is not necessarily used as a “stand-alone” diagnostic tool.
Anemia and FAMACHA
The level of anemia can be roughly evaluated by observing the color of mucous membranes in areas with many capillaries are close to the surface. Such areas are inside the lower eyelid, the gums and the vulva. If these membranes are quite pale, death is impending and deworming is indicated immediately. The FAMACHA© eye color chart system was developed in South Africa to help producers monitor and evaluate the level of anemia without having to rely on laboratory testing. In this method, the lower eyelid mucous membranes are examined and compared to a laminated color chart bearing pictures of sheep eyes at five different levels of anemia.:
- red, non-anemic;
- red-pink, non-anemic;
- pink, mild-anemic;
- pinkwhite, anemic;
- white, severely anemic.
Since anemia is the primary pathologic effect from infection with H. contortus (barber pole worm), this system can be an effective tool for identifying those animals that require treatment, but only for H. contortus. FAMACHA© has been extensively tested in South Africa and the United States with excellent results. It has been shown that where animals have been examined at weekly intervals and salvage treatments only were administered, up to 70 percent of adult animals may not require deworming, and only a few required more than one treatment. Compared to previous treatment regimens, the total number of treatments may be decreased by up to 90 percent. Since most of the worms would not be exposed to dewormers, this reduces the development of dewormer resistance. Information on FAMACHA© and training workshops held in many localities can be found on the Web Site of the American Consortium for Small Ruminant Parasite Control (ACSRPC,http://www.acsrpc.org ).
Worm Count and Identification
The most absolute and direct method for documenting the number of worms present in an animal is to open it up immediately after death or slaughter and collect, identify and count the worms present. This can only be done with high accuracy by a properly trained veterinarian or other professional, and can be expensive. However, a farmer can get an idea of the magnitude of H. contortus infection by looking for the worms that are visible on the lining of the abomasum. It should be noted that for this to be of any value, the animal cannot have been dead for very long. The fresher the animal is after death, the greater the chance to find worms. This is because after death, the worms will move as far down the gut as they can get and eventually die. It is important to note that Telodorsagia and Trichostrongylus are too small to see except under a microscope. Even if thousands of these worms are present, they cannot be seen by the naked eye while mixed in with the gut contents.