Wednesday, March 14, 2012

Haemonchus contortus: A Bite in the Gut

         Haemonchus contortus is a strongylid nematode that parasitizes the intestines of primarily sheep and  goats. This parasite, among others, is responsible for the decreased growth and reproduction rates, which greatly affects the goat and sheep industry. “Anemia, low packed cell volume (PCV), diarrhea, dehydration, peripheral, and internal fluid accumulation” are all symptoms of Haemonchosis. This parasitic relationship is particularly problematic in the southeastern part of the United States [1] and in tropical and subtropical regions [2]. Additionally, there is a growing resistance to antihelminth treatments, which makes the parasite difficult to control [1]. Although the data on the epidemiology of the H. contortus is well-gathered in more industrialized countries, data is lacking in underdeveloped countries. This data assists in establishing techniques of avoiding this parasite, due to its high potential to cut into economic profit [2].

Symbiont description
(Genus: Haemonchus; Species: contortus) 
            Cylindrically shaped nemotode, H. contortus  is sometimes called “barber poles,” particularly the females that have white ovaries and are also red due to the means nutrition – blood [3]. H. contortus has a complete digestive system and survives mostly in wet environments, especially the moist environment of a goat and sheep pasture [1]. More rainfall generally means a greater abundance in such areas. It lives in goat feces, and is therefore spread in that manner [2]. As studied under a microscope, the size of an egg is 70-85 micrometers x 41-48 micrometers. There are many parasites similar to one another that competitively parasitize the same sheep or goat. Therefore, it is useful to take accurate measurements of the egg [4]. The adult parasite (approximately 10-30 mm) has a cuticle layer that allows it to survive in the digestive tract of animals [3].

Host description

Bottlejaw: symtom of presence of H. contortus.   
         Primarily goats and sheep are the definitive hosts of H. contortus. The life cycle of this parasite does not have any intermediate hosts. Sheep and goats have a chambered stomach similar to cows. This nematode mostly resides in the adult form in the abomasum, the fourth and last chamber of the stomach and are passed through the digestive tract and into the feces. There are several reasons why sheep and goats are susceptible to H. contortus. Firstly, the feces of the host is pelleted, allowing the parasite easy access to the next host as the feces disintegrates. Sheep and goats are often kept in crowded areas, and they tend to graze even in areas of high fecal contamination. Additionally, these animals are flocking ones by nature. Like many illnesses, the old and young hosts are particularly susceptible to infection [5].  

Life cycle

Life cycle of H. contortus.   
            As 5,000-10,000 eggs per adult female are passed through the digestive tract, the nearly-hatched egg thrives in the moist environment of the feces and continues to develop in temperature-specific environments (75-85 degrees F). The development of the first stage larvae, called rhabditiform, may take 4-6 days to develop. The second stage larvae, filiariform type, actively climb to the top of the blades of grass to be ingested by the goat or sheep [6]. The third stage larvae then emerges after being ingested into the host, and as the cuticle is cast off, the parasite enters the fourth stage larva. Depending on whether the parasite enters an “arrest period,” the larvae either enters its fifth stage or proceeds to adulthood. Depending on the intensity of the infection, the adult parasite, may remove as much as one fifth of the erythrocyte blood volume per day by feeding on the blood of the inside of the gut [7].


Sign of Anemia.    
           This parasitic relationship can be devastating to the agricultural industry, as most goats and sheep bear little resistance to H. contortus and similar parasites. Hosts become extremely weak as they experience anemia and edemia.  When a sheep or goat owner vaccinates his animals, he is vaccinating them for a variety of parasites – not just H. contortus. However, evidence suggests that cross-breeding of certain breeds of sheep may be useful; some sheep seem to bear a natural resistance to some parasitic worms [8].

Example of Aggregated Distribution and Coevolution

Aggregated hosts.   

              The distribution of H. contortus is highly aggregated. Due to internal multiplication, the aggregation of parasites during infective stages, and most importantly, the behavior of the host, the parasite tends to be distributed aggregately. In addition, the relationship demonstrates the coevolution of parasite and host. Although most sheep and goats bear little resistance to H. contortus, the breeds that do bear resistance suggests coevolution. The parasite certainly inflicts virulence upon the host, as the host loses fitness as it succumbs to its parasitic counterparts [9].


[1] Lenira Leite-Brownin, M. (2006). Haemonchus contortus (barber pole worm) infestation in goats. Alabama Extension Cooperative System, Retrieved from  

[2] Fiaz Qamar, M. Azhar Maqbool, Muhammad Sarwar Khan, Nisar Ahmad, and Muhammad Akram Muneer (2009). Epidemiology of haemonchosis in sheep and goats under different managemental condition. Alabama Extension Cooperative System, 2(11), Retrieved from No.11 Full Text/Epidemiology of Haemonchosis in sheep and Goats under differ.pdf

[3] Sendow, J. (2012). Haemonchus contortus. Retrieved from

[4] Sloss, M. and R. Kemp. (1978). Veterinary clinical parasitolgy. (5 ed., p. 45). Ames, Iowa: Iowa State College Press.

[5] Whittier, W. D. (n.d.). Control of internal parasites in sheep. Retrieved from

[6] Haemonchus contortus. (n.d.). Retrieved from

[7] Georgi, J. (1990). Parasitology for veterinarians. (5 ed.). Philedelphia: W.B. Saunders Company.

[8] Correa, J., James G. Floyd, Lisa A. Kriese-Anderson. (1999, October). The use of sheep breeds resistant to internal parasites. Retrieved from

[9] Combes, Claude (2001). Parasitism. Chicago: The University of Chicago Press.