Haemonchosis

Haemonchosis also known as Stomach worm or Wire worm of Ruminants. It is caused by haemonchus contortus and H. Placei.

Etiology

• Haemonchus contortus: in sheep, goat and cattle.
• Haemonchus Placei: in cattle

Haemonchosis is a blood-sucking abomasal nematode may be responsible for extensive losses in sheep and cattle, especially in tropical areas.

Morphology

• Adult worm are larger in size (1-3 cm) and visible under naked eye, male even reddish in colour and female uneven reddish in colour due to twisting of ovaries around reddish intestine.
• The buccal capsule has slender tooth or lancet.

Epidemiology

• The frequency and severity of  outbreak is largely depends on rainfall in that particular area
• Survivability of larva is associated with ability to undergo hypobiosis.
• Resumption of development occurs just before the onset of seasonal rains.
• The sudden occurrence of  acute clinical haemonchosis is depends on high faecal worm egg output (2000 and 20000epg )and massive pasture contamination with L3 larvae.
• Sheep in endemic areas develop an acquired immunity, so that continuous contamination of the pasture occur.
• Epidemiology H. placei is similar to H. contortus.
• In addition to that cattle fecal pad acts as a reservoir of infective larvae of H. placei.
• In which the larvae survive for several months and ultimately released when fecal pad is sufficiently moistened by rain.

Host affected

H. contortus (Sheep & Goats)

• Age: Weaner age group (3 to 6 months) and lambed ewes are highly susceptible
• Breed: Native breeds are highly resistant (Presence of anti-larval IgA antibodies) to infection than exotic and crossbred sheep
• Hemoglobin type: Sheep having homozygous Hb type AA resistant to infection than sheep having heterozygous Hb type AB

H. placei (Cattle)

• Affect cattle less than 2 years old are highly susceptible.

Life cycle

Prepatent period

• H. contortus: 15 days
• H. placei: 30 days

Pathogenesis

Acute haemonchosis

• Acute hacmorrhagic anemia due to the blood sucking habits of the worms.
• Each worm suck 0.05 ml of blood/day.
• Sheep. Goat and cattle infected with 5000 H.Contortus may lose about 250 ml  blood daily.
• Anemia become apparent after two weeks of infection and is characterized by progressive and dramatic fall in PCV. During subsequent weeks haematocrit value stabilizes at low level, but at expense of two to three fold compensatory expansion of erythropoisis.
• However continual loss of iron and protein in gastrointestinal tract and increasing inappetence, the bone marrow eventually become exhausted. The haematocritic value  again falls before death.
• When ewes are affected, the consequent agalactia may result in the death of the suckling lambs.

Hyperacute haemonchosis

• Heavy infection of sheep with 30000 worm, the apparently healthy sheep suddenly die due to severe acute gastroenteritis.

Chronic haemonchosis

• It is important as acute haemonchosis.
• It develops during a prolonged period of  dry season, when reinfection are negligible, but pasture become deficient in nutrients.
• Continuous loss of blood  results from persistence of small worm burden(100-1000 infective larvae) in intestine.

Clinical manifestation

Hyperacute case

• Sheep die suddenly with haemorrhagic gastritis.

Acute haemonchosis

• Anemia, submandibular edema, ascities, lethargy, dark coloured faeces, loss of wool, diarrhoea is not generally a feature.

Chronic haemonchosis

• Progressive weight loss, weakness, neither severe anemia, nor gross edema being present.

Post mortem Finding

• Hydrothorax, hydropericardium and ascites.
• Watery blood.
• Abdominal fat – liquefied and become gelatinous in nature.
• Liver – light brown in colour is due to fatty changes.
• Abomasum- reddish-brown fluid ingesta and presence of worm on the mucosal folds and bite marks noticed on the abomasal mucosa.

Diagnosis

• Based on clinical signs
• Identification of eggs in faeces
• Fecal culture
• Autopsy of animal in the suspected flocks

Treatment

• When an acute outbreak has occurred the sheep should be treated with one of the benzimidazoles, levamisole,  avermectin, milbemycin or salicylanilide and allowed to graze in fresh pasture.
• Chronic haemonchosis is dealt with a similar fashion. If possible the new pasture should have a good nutritional value; alternatively some supplementary feeding may be given.

Control

Self cure phenomenon

• In an endemic area, the faecal egg count of sheep drops to zero level after a period of heavy rainfall is due to expulsion of major part of adult worm burden. This is called as self cure phenomena. The expulsion of adult worm as consequence of immediate hypersensitivity reaction to the antigens derived from developing larvae.
• Loss or expulsion of worm burden in the gastro-intestinal tract of the suitably infected and sensitized sheep can be induced by challenge dose of infective larvae.
• Self-cure and protection against infection are not necessarily interrelated – Immunity is not an absolute.
• Latent period of self cure induction is-6-7 weeks.

Host factor which induce Self cure phenomena

• Species: Sheep – it is well pronounced.
• Breed: Native breed of sheep having good response than exotic and crossbred sheep (due to presence of anti-larval IgA antibodies in the native breed).
• Age: Sheep greater than 6 months old having good response.
• Hemoglobin type: Sheep with homozygous Hb type AA having good response than homozygous Hb type BB.
• Stage of lactation: Relaxation of immunity – poor response.
• Level of lymphocytes in peripheral blood: Sheep with low level of lymphocytes having low immune response.

Immunity

• Cross immunity was observed between species of Haemonchus.
• Cross immunity occur between genus of Haemonchus and Trichostrongylus, but it is one way.
• Haemonchus induce immunity against Trichostrongylus and not vice versa.
• Exsheathed larvae induce good immunity than ensheathed larvae.
• Irradiated larvae induce good immunity.
• Size of the challenge dose is inversely related to the self-cure.