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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.


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