Round worms(new)

Round worms

Local names: 
Embu, Gikuyu, Meru: njoka / Gabbra: beni segara / Kamba: nzoka sya nda / Kipsigis: tiongik / Maragoli: tsinzoka / Samburu: ntumuai / Somali Ethiopia: goryan / Turkana: ngílomun /

Common names: : gastro-intestinal worms, gastro-intestinal Helminth, Nematodes

Description: Intestinal parasite, some are also found in the stomach

Introduction

Round worm infection, gastro-intestinal helminths or parasitic gastroenteritis, cause major economic loss in cattle, sheep and goat production.

The round worms are very small and vary in size from being visible to being almost invisible. - Several different species of worms with differing life cycles may be involved, but the symptoms they cause are all rather similar and difficult to differentiate in the living animal. Most round worms feed on nutrients inside the host animal’s intestines. Certain worm species can attach to the lining of the stomach or guts, where they suck blood. These blood-sucking round worms cause more severe disease and anaemia and can kill young animals.

Immunity is acquired slowly and is generally incomplete. Good nutrition increases the resistance of livestock against round worms. Young animals are generally more at risk than adults. But in sheep and goats the adults remain susceptible and suffer more from the effects of worms than in cattle. Especially ewes after lambing harbour large numbers of worms and can show diarrhoea and a drop in milk yield due to lowered immunity against the worms.

When treating animals with symptoms, the following should be considered:

• Provide adequate nutrition
• Treat all animals in a group as a preventive measure in order to reduce further pasture contamination
• Following treatment stock should NOT be moved to clean pasture as was previously recommended. The reason for this is that if any worms which are resistant to dewormers survive treatment then the clean pasture will become seeded with a completely resistant population of worms.

Resistance of worms against the drugs used (anthelmintic resistance) is a major and growing problem. Under-dosing, underestimation of body weight, overuse of anthelmintic drugs, random use of anthelmintics without a proper diagnosis, poor nutrition and rapid reinfestation all play a role in causing resistance. In some countries, such as Australia and South Africa, anthelmintic resistance is such a serious problem that it threatens the economic viability of sheep farming. In order to prevent such a situation from developing anthelmintics must be used correctly and with restraint.  A good strategy is NOT to deworm the whole herd but to rather target specific animals or groups of animals, examples:

• Deworm young animals to prevent stunting
• Deworm ewes at lambing
• Selectively deworm those individual animals showing severe anaemia, visible as pale membranes around the eyes

Such a targeted deworming strategy will also reduce the amount of money spent on anthelmintics.

When suspecting resistance of worms against an anthelmintic drug the following test can be carried out:

1. Immediately before deworming collect a pooled faecal sample from the group to be treated and send it to a laboratory for counting the number of worm eggs in the faeces (faecal egg count). This test is easy to perform in a lab and is not costly.
2. 7-8 days after the treatment collect a second pooled faecal sample from the group and send it to the laboratory for a repeat faecal egg count.
3. The comparison of worm egg numbers before and after the treatment will show whether the anthelmintic used is till effective or not.

Life cycle

The life cycle of the worms usually takes 2 to 3 weeks, but varies in relation to dry conditions, rainfall and temperature. The worm cycle is most active under cool and wet conditions leading to rapid build up of worm burdens in the stomachs and guts of grazing animals. It can almost stop when it is hot and dry.

Worm cycle:

• Eggs produced by the parasite are shed in the faeces of the animal onto the pasture.
• Out of these eggs hatch larvae which attach to grass and herbage.
• Larvae are then ingested by the grazing host.

Nematode parasites of cattle and sheep

1. Toxocara vitulorum

A round worm with a very specific life cycle, which does not affect mature cattle.  It occurs in the intestines of suckling calves and is present in most tropical countries. The calves become infected before birth and also via the milk. After ingestion the larvae penetrate the intestinal wall and migrate to other tissues of the host especially to the lungs, via the blood stream. The larvae are coughed up and then re-swallowed to re-enter the intestines, become adult worms in the intestines where they produce eggs. High numbers can lead to stunting of calves.

2. Haemonchus contortus

Also called the barber pole worm. It is a very aggressive and common blood-sucking stomach worm of cattle and sheep. It is found all over the world, but is less common or even absent from dry areas. It has a direct life cycle. Infective larvae can survive for several weeks on pasture under wet conditions. After the larvae are ingested by the host, they become adults, attach to the lining of the stomach and start suckling blood. Depending on the numbers of worms present in the stomach this can lead to severe anaemia and even death in young animals. Worms on the lining of the stomach are visible at post-mortem as very fine reddish small threads. They can easily be overlooked if the post mortem is not done carefully.

3. Trichostrongylus species

There are several species of this worm widely spread in the tropics. The worm is brownish, pinkish in colour and is found in the stomach and small intestine of cattle, sheep and goats. They thrive on nutrients absorbed from the contents of the gut.

Trichostrongylus tenuis are small hair like nematodes usually less than 7 mm long and difficult to see with the naked eye.

© Dr. John W. McGarry and the School of Vet Science in Liverpool

4. Cooperia species

These are small, red coloured worms found in the small intestine of most ruminant animals. They have a direct life cycle similar to Trichostrongylus.

5. Ostertagia species

They are mainly found in the stomach and occasionally in the small intestine of livestock. They have a direct life cycle and are able to survive longer outside the host even under harsh conditions. They normally infect pasture during the onset of the long rains.

6. Nematodirus species

They are found in the small intestine of livestock. The eggs can survive harsh environmental conditions on the pasture. When environmental conditions improve (rainy and wet) the larvae hatch and the pasture all of a sudden becomes infectious for grazing animals.

7. Chabertia species

They are also known as the large mouthed bowel worms. They are found in the large intestine of most ruminants. The larvae penetrate and embed in the wall of the intestine.

The signs of round worm infection are shared by many diseases and conditions, but based on certain symptoms, grazing history, and season, a presumptive diagnosis can be made.

• Young animals are most often affected, but adults not previously exposed to infestation frequently show signs and succumb. Animals in a state of poor nutrition are more susceptible than animals in good condition. 
• Ostertagia and Trichostrongylus infestations lead to profuse watery diarrhoea which is usually persistent.
• Haemonchus causes constipation and variable degrees of anaemia. - In sheep infected by large numbers of Haemonchus the conjunctiva (the mucous membrane that lines the inner surface of the eyelid and the exposed surface of the eyeball) can be snow white in colour.
• Heavy worm infestation results in progressive weight loss, weakness, a rough coat, loss of appetite, and oedema, particularly under the lower jaw – a condition termed as bottle jaw. 
• Toxocara can cause in rapid breathing and coughing in young calves.

Note that egg counts are not always an accurate indicator of the number of adult worms present as egg laying is not always constant; some species of worms lay more or less eggs than others, and  immature worms and larvae are not egg layers.

Some worms are much more aggressive than others. For example 100 Haemonchus worms in a lamb do as much damage as 5,000- 10,000 Ostertagia worms.

Post mortem findings and Diagnosis

Adult worms are usually visible to the naked eye. Some are more easily seen than others. Worms may be only visible due to their movement in fluid stomach and intestinal contents.

• The mucus membranes are often pale.
• The carcass may be emaciated, but in some instances where an animal has been overwhelmed by a sudden massive invasion of larvae the carcass may be in good condition.
• The abomasum is frequently fluid filled and this may exend into the small intestine, especially in Haemonchus infestations.
• The liver is pale and fragile
• The alimentary tract will reveal worms when opened. Check especially the stomach, and the large intestine.

Prevention – Control - Treatment

Round worm infestation can be controlled through adherence to the following measures:

• In young cattle round worm infection can be controlled by the use of broadspectrum anthelmintics (drugs to expel worms) in conjunction with pasture management to limit reinfestation.
• Pasture management includes a move to clean pastures e.g. grass conservation areas or hay aftermath, or alternate grazing with other host species, or integrated rotational grazing in which susceptible calves are followed by immune adults.
• A special strategic treatment is required in sheep to counter the low immunity seen in ewes around lambing time. Treatment within the month before and the month after lambing should be given. Supportive management after treatment includes movement of sheep from contaminated pastures to cattle pastures, grass conservation areas, or pastures not grazed by sheep for several months. This period may vary from several weeks to several months depending on the weather pattern (longer if wet and cool, shorter if dry and hot).
• Resting pasture for more than 10 weeks will reduce the number of infective larvae on pasture. Separating young and mature animals in grazing paddocks or grazing different species of animals together. These practices will help to reduce parasite mass and reduce infestation levels.
• Better grazing management should avoid overstocking of animals on a particular paddock. Grazing management should also ensure that there are alternative grazing areas, should avoid damp grazing areas and always ensure that animals are in good condition. Well nourished animals are less likely to acquire heavy worm infestations.

Treatment

The following treatments and drugs are recommended for round worms.

• Albendazole should be administered orally at the end of the cold season and beginning of the dry season. The drug should be given at the rate of 10 mg/kg body weight
• Fenbendazole should be given at the end of the cold and beginning the dry season by mouth at the rate of 8 mg/kg body weight
• Ivermectin can be used in different forms such as injection, orally, or as a pour on. Should be given at the rate of between 0.2 - 0.5 mg/kg body weight as a subcutaneous injection. Giving anthelmintics by injection is recommended as it avoids the risk of damage to the animal’s throat through rough drenching and none of the drug is lost.
• Levamisole and oxyclazanide in combination should be given by mouth at 0.25 ml/kg body weight
• Albizidal antihelmintica as a botanical treatment- the leaves of the tree are fermented and sieved and administered orally.

NB. Always follow the manufacturer’s recommendations when administering drugs.

Common traditional practices

Though traditional wormcure is practiced widely, reports have also been shared where traditional treatment has killed the animals under treatment. Dosage is very difficult as active content of plants vary depending on season and stage of growth. It is safer to use the commercial products with known dosis rate. If this is not available seek advice from the local herbalist.

• Luo (cattle, goats, sheep): Cut about 2kg of fresh awayo (Rhus vulgaris) roots, put in 1 kg of water and leave overnight. Sieve and drench with 0.5 litre once a day for a week. Give half this dose for calves, goats and sheep. Give when it is cool and after the animal has eaten. 
• Embu / Gikuyu (cattle, goats, sheep): Collect 2 handfuls of dry seeds of mugaita (Rapanea melanophloeos). Crush and mix with 1 litre of water. Boil gently for 20 minutes. Allow to cool, then drench once. For goats, sheep and calves use 500 ml; for large animals use 1 litre. Drenching should be done in the evening when it is cool. Repeat after 2 weeks. 
• Kipsigis (cattle, goats, sheep): Crush 0.25 kg of matakarek (Rapanea melanophloeos) and mix in 1 litre of water. Let boil for 15 minutes. Allow to cool then drench the whole amount once. For small animals use 500ml; for large animals use 1 litre. Repeat after 3 weeks. 
• Samburu (camels, cattle, goats, sheep): In the rainy season drive animals to areas with salty soils when the water has dried up. The animals will lick the salt from the surface of the ground. 
• Maragoli (cattle, goats, sheep): Chop 2 bulbs of saumu (Allium sativum) and mix with 4 litres of water. Drench with 0.5 litres twice in 1 day. This treats worms and liverflukes. The dose is the same for adult cattle, sheep and goats. 
• Somalia Ethiopia: Grind 2 fruits of Gosso (Hagenia abyssinica) in 0.5 of water . Drench a sick cow with this before it goes to pasture. Use half the amount for goats and sheep.