Haemonchosis in Ruminants

Haemonchosis is one of the most pathogenic blood sucking nematodal infestation of sheep, goat and cattle and it occurs in the fore stomach of the above animals.

Aetilogy

The nematode, Haemonchus which affects sheep, goat and cattle is closely related to other trichostrongylids of ruminants. Haemonchus contortus is most commonly found in sheep and goat while H. Placei is the usual specias in cattle. But cross-infestations may occur, which are usually of lesser severity. Another abomasal trichostrongylid, Mecistocirrus digitatus occrus in sheep, cattle and buffalo causing a disease very similar to haemonchosis. Haemonchus is popularly known as ‘stomach worm’. ‘wire worm’, ‘Barber’s pole worm’.

Incidence

Haemonchosis is world wide in distribution, but predominant in tropical part of the world; Northern part of India. M. digitatus occurs in the Orient and in Central America.

Life Cycle

Eggs are passed in the faeces and hatch in favourable climatic condition. After passing 1st and 2nd larval stages, the infective 3rd stage larvae come out which are accidentally ingested by the animals while grazing. On reaching the abomasum, they undergo 3rd and 4th moults and reach maturity. Many thousands of worms may occur in a single ruminant stomach and it has been estimated that 4000 worms suck about 60 cm cubes of blood per day. Male and female worms unite and lay-eggs within 3 weeks.

Clinical Findings

Haemonchosis causes heavy losses due to deaths and reduced production.

Lambs and young sheep are commonly affected by acute form of the disease. There is loose, bloody diarrhoea and the mucous membrane and conjunctivae o such sheep will be extremely pale due to severe anaemia. Viscosity of blood will be lowered down and it will be watery. The animal will very weak, recumbent and die consequently.

Most of the animals suffer from chronic form of the disease. Affected animals become gradually weak, lethargic, show paleness of mucosae and conjunctivae, cachectic condition, loose stool, anaemia and anasarca particularly under the lower jaw and to a lesser extent along the ventral abdomen. Affected sheep in a flock while driven are noticed to lag behind, breathe faster, have a staggering gait and often go down. Some sheep may die as a result of exercise. There is loss of body weight and detrimental effect on wool growth and quality. Sheep not fatally affected develop a break in the wool and he fleece may be lost at a later date.

In calves, the disease is characterised by severe anaemia and anasarca.

Diagnosis

1. Clinical manifestations – anaemia and diarrhoea
2. Postmortem examination – mat formation in abomasum
3. Faecal examination for detection of eggs – eggs of Haemonchus spp. can not be easily differentiated from those of many other GI nematodes.
4. Faecal culture for identification of infective larvae. At necropsy, counts of 3000 H. contortus in lambs and 9000 in adult sheep are usually associated with heavy mortalities.
5. Clinical Pathology – There is significant rise of abomasal pH soon after infection accompanied by increased plasma pepsinogen and gastrin concentrations.

Differential Diagnosis

1. Sheep: Other causes of sudden death, such as lightning stroke, snake bite, anthrax or enterotoxaemia are often suggested by the farmer and can only be differentiated by necropsy.
2. Calves: Haemonchosis has to be differentiated from Babesiosis, Anaplasmosis, Coccidiosis, Hookworm infection, etc.

Treatment

Principles of treatment are:

• Regular treatment is necessary.
• Switching of one drug to another to avoid drug resistance.
• Study of randomised faecal sample.

Drugs

1. Benzimidazole compounds:

Albendazole, Fenbendazole, Cambendazole, Mebendazole etc.

Dose: 5-10 mg/kg body weight 

2. Levamisole:

Dose: 7.5 mg/kg orally or 5 mg/kg S/c

3. Pyrantel and Morantel:

Dose: 11 mg/kg orally

4. Ivermectin @ 0.2 mg/kg S/c

5. Closantel, Rafoxanide, Nitroxynil are also used.

6. Closantel and disophenol exert a persistent protective effect in sheep for up to 4 weeks. With closantel this period can be extended by reducing feed intake for 24 hours before treatment to enhance the uptake of drug.

Control

The following measures are of utmost importance in the control of Haemonchus infection in ruminants.

1. The animals should be well fed and supplied with licks containing those minerals in which the pasture is deficient. Well nourished animals are usually much less susceptible to infection than others and even if some worms do establish themselves, their effects are hardly noticed and a spontaneous cure soon occurs.
2. The animals should be regularly treated in order to keep them free from harmful worms.
3. Overstocking tends to concentrate worm infection and should therefore be avoided. On the other hand, pasture rotation allows the animal to graze on clean pastures at intervals while the infected paddocks can be left to become clean, Small ruminants are grazed sequentially for up to 4 days on a series of suitability sized small plots, each of which is rested for at least 30 days before re-use.
4. Because calves, lambs and young sheeps are most susceptible to worms, they should be separated from their mothers as early as possible and graze in a clean paddock.
5. Wet or moist pastures as well as other wet places like edges of pools of water or dams, which present very suitable conditions for the development and maintenance of worm larvae, should be avoided.
6. Frequent treatment with broad spectrum anthelmintics can lead to the development of anthelmintic resistance. Control programmes have therefore been advised by utilizing a sustained acting compound such as closantel, disophenol or moxidectin. Treatment with closantel in late winter kills hypobiotic larvae and subsequently over wintering larvae from the pasture as they are ingested. Ivermectin bolus can be used.
7. Vaccination is a more attractive possibility and considerable progress is being made in this direction. An experimental molecular vaccine based on H. contortus hut membrane antigen has been shown to reduce faecal egg counts by 90% and worm number by 70-80%. Young lambs can be protected by passive transfer of colostral antibodies from vaccinated ewes.