1. Initial surveys for determining the parasite species present

1.1 Introduction
1.2 Parasite groupings
1.3 Identification procedure

1.1 Introduction

As a first step in the investigation of helminth infections of ruminants, it is important to establish what parasite species are present in an area, country or region. This may already be well documented, in which case this step is not necessary. However, the dominant parasites in an area can change, particularly as livestock management practices change, so existing parasite inventories as well as distribution data based on old studies may require updating.

Initial surveys should be kept extremely simple. They are intended to identify parasites present rather than to determine their importance, a later procedure.

While it may be relatively easy to identify some helminth parasites of ruminants simply on the basis of the tissues and organs in which they are located, it may be difficult to identify gastro-intestinal parasites. Many of the gastro-intestinal nematodes look alike but they can be identified down to a species level by microscopical examination. In addition, most of them live in specific sites in the intestinal tract, which helps in the identification process. Since different species have different pathogenic effects, it is important to know which broad groups are present in a herd or area. Furthermore, some of these parasites have very different development times, both outside and inside the host, a knowledge of which is important for effective control measures.

1.2 Parasite groupings

1.2.1 Nematodes
1.2.2 Cestodes
1.2.3 Trematodes
1.2.4 Protozoa

Helminth parasites can be classified into four broad groups.

1.2.1 Nematodes

Haemonchus	Bunostomum (hookworms)
Ostertagia	Strongyloides
Trichostrongylus	Oesophagostomum
Mecistocirrus	Chabertia ovina
Cooperia	Trichuris (whipworms)
Nematodirus	Dictyocaulus
Protostrongylus	Parafilaria
Muellerius	Onchocerca
Toxocara	Setaria
Stephanofilaria	Thelazia

1.2.2 Cestodes

Monezia	Cysticercus bovis
Avitellina	Cysticercus tenuicollis
Thysaniezia	Coenurus cerebralis
Stilesia	Hydatid cysts

1.2.3 Trematodes

Fasciola	Paramphistomum
Dicrocoelium	Schistosoma

1.2.4 Protozoa

Coccidia* (Eimeria)

* Members of this family Eimeriidae are referred to here as Coccidia

As the protozoan parasites usually referred to as coccidia are commonly found in the intestines of ruminants, this manual will cover the main features of the epidemiology, diagnosis and control of these parasites.

1.3 Identification procedure

1.3.1 Post-mortem examination
1.3.2 Identification of parasite eggs in faecal samples from live animals

The identification of parasites present in an area can be carried out in the following two ways:

· a post-mortem examination of animals

(a) that have died from acute or chronic diseases or
(b) that have been slaughtered at a slaughterhouse/slaughter place

· the identification of parasite eggs and larvae present in faecal samples from live animals.

1.3.1 Post-mortem examination

1.3.1.1 Gastro-intestinal tract
1.3.1.2 Liver
1.3.1.3 Lungs
1.3.1.4 Other organs and tissues

Generally the most useful data will be acquired from young animals and those that have not been recently dewormed. The entire gastro-intestinal tract (rumen to rectum) should be obtained from slaughterhouses/places, butchers, veterinary diagnostic centres, etc., for the purpose of calculating the total number of parasites present (see a description of this procedure in section 4.3), as well as identifying the species found. This procedure should be performed towards the end of the rainy season.

Table 1.1 PARASITES LOCATED IN THE GASTRO-INTESTINAL TRACT AND THEIR EFFECT

Site	Host species	Parasites	Action
Rumen	Cattle	Paramphistomum	Mucosal damage
Abomasum	Cattle, sheep, goats	Haemonchus	Blood sucking
		Mecistocirrus	Blood sucking
		Ostertagia	Mucosal damage
		Trichostrongylus axei	Mucosal damage
Small intestine	Cattle, sheep, goats	Trichostrongylus	Mucosal damage
		Bunostomum	Blood sucking
		Cooperia	Mucosal damage
		Nematodirus	Mucosal damage
		Strongyloides	Mucosal damage
		Paramphistomum larva	Mucosal damage
		Coccidia	Mucosal damage
		Monezia	Minimal
Large intestine	Cattle, sheep, goats	Trichuris	Blood sucking
		Oesophagostomum	Mucosal damage, nodules
	Sheep	Coccidia	Mucosal damage
		Chabertia ovina	Minimal

The identification of parasite species is described in Chapter 4.

1.3.1.1 Gastro-intestinal tract

Most gastro-intestinal parasites live in distinct sites of the intestinal tract. The location of parasites in the intestinal tract of different ruminant species is shown in Table 1.1. Parasites vary also in their geographical distribution which depends particularly on climate (especially rainfall), vegetation and livestock density.

1.3.1.2 Liver

The liver should be examined for migratory tracts (caused by immature Fasciola and Cysticercus tenuicollis larvae), swellings (hydatid cysts and Schistosoma nodules), enlarged bile ducts (adult Fasciola) and relatively large transparent cysts attached to the surface of the liver (Cysticercus tenuicollis). The presence of parasites associated with these lesions can be confirmed by incisions in the liver parenchyma. Following incision, Dicrocoelium and Stilesia may be observed in the bile ducts.

Table 1.2 PARASITES LOCATED IN THE LIVER AND THEIR EFFECT

Site	Host species	Parasites	Action
Parenchyma	Cattle, sheep, goats	Immature flukes Fasciola hepatica, Fasciola gigantica	Destruction of tissue, fibrosis
		Larval stages of Cysticercus tenuicollis	Fibrotic tracts, calcified nodules
		Eggs of schistosomes	Granulomas, destruction of tissue
		Hydatid cysts	Pressure atrophy
Bile duets	Cattle, sheep, goats	Mature flukes Fasciola hepatica, Fasciola gigantica	Blood sucking, destruction of bile ducts, fibrosis
		Dicrocoelium	Minimal (fibrosis)
		Stilesia	Minimal
Liver capsule	Cattle, sheep, goats	Cysticercus tenuicollis cysts	Minimal

1.3.1.3 Lungs

Several species of lungworms may cause pathological changes and the post-mortem examination of the lungs may reveal signs of bronchitis, pneumonia, pleuritis, swellings and nodules. Adult Dictyocaulus species are found in the trachea and the main bronchi, Protostrongylus in the terminal bronchioles and Muellerius are usually embedded in grey nodules formed around the alveoli. The lungs are an organ in which hydatid cysts may be located and associated swellings can often be seen or palpated. Occasionally nodules containing liver flukes may be found in the lungs.

Table 1.3 PARASITES LOCATED IN THE LUNGS AND THEIR EFFECT

Site	Host species	Parasite	Action
Trachea	Cattle, sheep, goats	Dictyocaulus	Tracheitis,
Bronchi	Cattle, sheep, goats	Dictyocaulus	Bronchitis pneumonia
Bronchioles	Sheep, goats	Protostrongylus	Pneumonia, pleuritis
Alveoli	Sheep, goats	Muellerius	Nodules
Lung tissue	Cattle, buffalo, sheep, goats	Hydatid cysts	Tissue atrophy

1.3.1.4 Other organs and tissues

The larvae of some cestode species may be found in muscle tissues of cattle (Cysticercus bovis) and sheep (Cysticercus ovis). The cysts are 6-9 mm in size and semi-transparent when young. As a result of the host's immune response they gradually degenerate, becoming caseous and eventually calcified. The predilection sites are the heart muscle, the tongue, the masseters and the diaphragm.

Some of the filarial worms are found in nodules located in ligaments and tendons (Onchocerca species), in muscles (Onchocerca) and in the skin or subcutaneous tissue (Onchocerca, Parafilaria, Stephanofilaria). Others are found living in the body cavities (Setaria).

Parasites of the conjunctival sac and/or lachrymal duct (Thelazia) may be very prevalent in some areas.

1.3.2 Identification of parasite eggs in faecal samples from live animals

Fresh faecal samples should be taken from a small number of animals. These samples should be taken preferably towards the end of the rainy season from young animals and those that have not recently been dewormed.

Collected faecal samples should be subjected to a flotation and sedimentation procedure for separating and concentrating parasite eggs (see section 3.3) and examined microscopically. In addition the sample should be subjected to a Baerman examination for isolation of lungworm larvae (see section 3.6). The eggs of some parasites are easy to differentiate. The following are examples of these parasites.

Table 1.4 PARASITES LOCATED IN VARIOUS ORGANS AND TISSUES AND THEIR EFFECT

Site	Host species	Parasite	Action
Muscle	Cattle, buffalo, sheep, goats	Cysticercus Onchocerca	Minimal Minimal
Ligaments, tendons	Cattle, buffalo	Onchocerca	Minimal
Skin and subcutaneous tissue	Cattle, buffalo	Onchocerca, Stephanofilaria, Parafilaria	Minimal Minimal Nodules, damage to carcass surface
Body cavities	Cattle, buffalo	Setaria	Minimal
Central nervous system	Cattle, buffalo sheep, goats	Setaria larvae	Neurological disturbance
	Sheep, (goats, cattle)	Coenurus cerebralis	Neurological disturbance
Circulatory system	Cattle, sheep, goats	Schistosomes	Minimal *
Eye	Cattle, sheep goats	Thelazia	Minimal

* Note: Most of the pathogenic effect of schistosomes is related to the migration of the eggs.

Trichuris

Strongyloides

Nematodirus

Monezia

Paramphistomum

Coccidia oocysts

The eggs of other parasites, however, are similar in size and structure and cannot easily be differentiated. These include the Trichostrongyles, Oesophagostomum and Bunostomum. To differentiate and identify these nematode eggs, faecal cultures may be set up for each faecal sample or group of samples (see section 3.5). Faecal cultures allow parasite eggs present in the faeces to develop into larvae. The third-stage larvae (L₃) are then isolated from the faecal cultures and used to identify definitively the parasites at the species or genus level. This is described in Chapter 3.