Wireworm- Haarwurm
By Dr Mackie Hobson BSc(Agric),BVSc

Haemonchus contortus known as ‘Wireworm’ or ‘Haarwurm’ are one of the most important health issues facing the Angora goat industry.

Wireworm occur in the abomasum of the goat and the females worms can easily be identified by the white ovaries twisting around the blood filled gut and so called ‘barber’s pole’. They are usually 2-3cm long.

The blood-sucking nature of wireworm can cause the loss of 0.05ml of blood a day.

The number of worms in the Angora goat abomasum determines the amount of blood loss a day.

To get an idea of the number of worms present in the abomasuma faecal sample can be checked for the number of
eggs per gram (epg).

On post mortem if later than 24hrs after death the worms may no longer be visible.

Anaemia caused by wireworm can occur due to haemorrhage from the abomasum wall in per acute infestations. In more chronic forms the anaemia may be aggravated by the depletion of iron reserves which reduced the ability of the goat to manufacture new red blood cells. The blood protein, albumin, becomes reduced resulting in the drop of blood oncotic pressure, oedema and ‘bottle jaw’ and ‘swelsiekte’. Some Angora goats that are chronically infected over months may lose weight and get weaker but not show significant anaemia or oedema.

Immunity of the Angora goat to wireworm

The immunity of the Angora goat to wireworm is poor. It has been demonstrated that genetic factors play an important role and the selection for resistance to wireworm is an important tool that needs to be used within the Angora industry.

SEE Immunity in Angora goats https://www.angoras.co.za/article/immunity-in-angora-goats

Immunity to wireworm affects worm burdens in 3 stages:

1. Fewer incoming worm larvae establish and become adults
2. Established female worms produce fewer eggs
3. Established adult worms are rejected by the goat

Innate immunity in an individual animal is the inherent ability of that animal to resist infection with worms and is genetically predetermined and inherited. Acquired immunity develops after goats have been exposed to worms. Adult goats have a better acquired immunity whereas kids until 9 months old have very poor acquired immunity and are reliant on their genetic status.

The immunity of individual animals can be influenced by multiple factors.

a. Pregnancy and lactation. Normally about 5% of infective L3 stage larvae establish as adult worms but this increases to 30-40% during late pregnancy and lactation.

b. Nutritional plane. Nutrition is vital in maintaining a good immune system and many studies demonstrate the much better immune response by heavier kids.

c. Selection for certain production traits. This may have inadvertently led to decreased immunity. It is interesting to note that fibre diameter (fineness) has been correlated to higher worm burdens (poorer worm immunity) in sheep so we would expect the same would be likely to apply in goats.

Selection for resistance going into the future will be vital for the progress of the Angora industry.

Selection can be done using Faecal eggs counts (repeatability is high) and the FARMACHA system.

SEE Breeding worm resistant Angora goats: https://www.angoras.co.za/article/breeding-worm-
resistant-angora-goats

Wirevax vaccination is available but used off liscence in Angora goats.

In the future Genomic selection using DNA markers will likely be used.

• The Single Nucleotide Polymorphisms (SNP) chips have proven to have an accuracy (0.5) when selecting for faecal egg counts in sheep. This is higher than traits such as weaning weight and fleece weight.
• BLUP accuracy in selection for faecal egg counts is even better with certain breeds having an accuracy of (0.63-0.70).
• On farm flock selection can be as simple as carrying out Target Selection Treatment (TST) using FARMACHA and marking goats and culling repeat offenders.

Seasonal effect of wireworm.

The rise in the adult wireworm population in spring may be due to

1. The relaxation of resistance with the Angora ewes kidding and lactating
2. The effect of ‘hypobiosis’ where the L4 larval development is retarded over the winter months and continues its development as the environmental conditions improve in spring.
3. The infective larvae on the pasture survive more easily as the temperatures rise and moister environmental conditions.

As the summer progresses further contamination results in the higher levels see in late summer especially in weaned kids under stress.

Wireworm Life cycle

Each female can produce up to 10 000 eggs per day and so pastures and the veld and lands can be rapidly contaminated. The eggs hatch in 4-6 days and L1 stage larvae develops. These larvae feed on the bacteria in the faeces and develop into stage L3 larvae. These larvae crawl up moist
vegetation and wait to be eaten by the goat.

The larvae are protected by a cuticle but under dry or very hot or frosty conditions do not survive for long periods. For this reason resting camps for 2-3 months helps in worm control.

The Larvae are eaten by the goat move through the 3 stomach to reach the abomasum where the protective cuticle is shed. The larvae moult and develop into the L4 stage within 48 hrs. They penetrate the lining of the abomasum and start feeding on the blood and can be seen as a small
blood clot on the abomasum wall. After about 3 days the L4 develop into an adult worm which attach to the abomasum wall and suck blood.

The developmental period is about 18-21 days.

The developmental period of 18-21 days is the reason the faecal egg count reduction test (FECRT) involves taking a faecal sample about 10 -14 days after the anthelmintic has been given -any eggs found then will have to be produced by worms surviving the dose.

It is interesting to note that when Trichostrongylus axei (bankrupt worm) has been present in the wireworm takes some time to establish itself in the abomasum, possibly due to the environment created not being suitable.

Management Strategies for roundworm control must be part of every Angora goat farm.

SEE https://www.angoras.co.za/article/roundworm-management-strategies-in-angora-goats#241