Clinical Diagnosis of Sheep Diseases
Introduction
Sheep are domesticated ruminant that are widely distributed throughout the world. More than 16 sheep breed are known. In Saudi Arabia
Many problems are facing sheep rearing but diseases are top in the list facing sheep industry.
Types of diseases in sheep
1-Infectious
2-Non infectious
Infectious diseases
ُExamples | Infectious Agent |
Clostridial diseases, foot rot, some types of pneumonia (Pasteurllosis), some abortion diseases, (brucellosis), bacterial mastitis | Bacteria |
Foot and Mouth, sore mouth, rabies, pox | Virus |
coccidiosis, worms, mange | Parasite |
prions are proteins normally found within the body’s nervous tissue (nerves, spinal column, brain) ·for unknown reasons these prions at times will change to a form that resists the normal mechanisms for turn over and break down ·prions continue to buildup on the nerve tissue eventually causing nervous disorders (Scrapie) | Prions |
Noninfectious diseases
Type | Information | Examples |
Nutritional | ·deficiency or excess of particular nutrients in the diet ·can be acute (occur suddenly), but most often is a gradual depletion or buildup of nutrient | White muscle disease, photosensitivity, copper toxicity |
Metabolic | ·closely tied with nutritional disorders as they are caused by an imbalance in the nutrients supplied in diet with production demands ·Accumulation of metabolites ·animal’s metabolism can not meet the production demands and nutrients are extracted from the animal’s system at a greater rate than they can be replenished ·typically rapid onset of signs ·occurs at times of sudden increases production requirements (e.g. when a ewe begins lactating) or with sudden changes in diet (e.g.hay diet directly to lush pasture) | Pregnancy toxemia, hypocalcaemia, grass staggers |
Digestive | ·also linked with nutrition and changes in diet ·generally caused by a disruption in rumen function | Bloat, Lactic acidosis |
Genetic | ·defects which are inherited from parents ·intensive line breeding or inbreeding programs generally cause an increase in these disorders ·keeping good breeding and lambing records will greatly aid in culling the problem out of your flock | overshot jaw |
What is diagnosis?
Identification of the disease or condition that affecting the animal at present time.
Diagnosis of sheep diseases is important due to the followings:
1) Accurate and early diagnosis is particularly important for the clinical treatment of diseases
2) Diagnosis is the cornerstone of any control program
3) Diagnosis is important as it gives insight into the extent of public health problems (zoonotic disease transmitted from sheep).
Types of diagnosis
i) Tentative
ii) Confirmatory
iii) Differential
Tentative
Could be achieved by:
1-Full clinical history
Including the age, sex species and any related information
Age (different diseases will be more likely to occur in certain age)
Gender and reproductive state (e.g. ewes which are very heavily pregnant or that have just lambed) showed by the animal at time
Number of animals affected and pattern of affection. (e.g. problems such as a lack of water or toxins in feed may acutely (suddenly) affect all animals in the pen, while infectious diseases may affect a small percentage of animals initially, and gradually move through the pen and/or barn.)
2- Lesions
Some sheep diseases have characteristics (pathognomic lesions) eg: pox
3- Clinical Examination
Could be visual or physical
Visual:
Check animal for
Rrumination
Looked ‘depressed’: head down, droopy ears, dull eyes, hunched stance (back arched with forefeet and hind feet placed close together under the animal)
Look hollow (abdomen/flank is excessively concave and hook bones are prominent)
Show signs of diarrhea (excessive tag or wetness on hindquarters are key signs)
Show signs of bloat (distension of abdomen, particularly high on the left side where the rumen is located)
Show signs of respiratory distress (laboured breathing, nostrils distended, coughing, copious amounts of nasal discharge)
Show signs of neurological disorders (uncoordinated, moving in circles, abnormal gait, posture or head carriage)
Show signs of lameness or stiffness
Physical examination
Body temperature (normal for an adult is 39-40 c0)
Notes: Some physiological factors will affect body Tem, (Age, lambs are normally higher than adults, day time, environmental temp.)
A high body temperature indicates that the animal is stressed or the body is staging an immune response to an infection.
A normal body temperature indicates that the problem is due to a noninfectious cause, such as a metabolic disorder
A low body temperature in very young lambs indicates starvation, and in adults may indicate internal bleeding.
Body temperature can be taken by gently inserting a thermometer into the sheep’s rectum. Using a bit of mineral oil or other nontoxic lubricant will make the process easier. Be sure to hold the thermometer while you are taking the temperature, to prevent it from become lost or broken. If you are using a glass thermometer it should remain in the animal for at least 60 to 90 seconds to ensure an accurate result. Digital thermometers signal when the temperature has stabilized
Auscultation to check
1-Heart rate (normal for a sheep is 70-90/ minute). Heart rate will increase under the same circumstances as the respiration rate.
2-To hear respiratory sounds and rumen sounds. Respiration rate (normal for a sheep is 25-35 (respirations/minute) (this also can be observed visually)
An abnormally high rate is an indication of distress caused by diseases that attack the respiratory tract (such as pneumonia), or could be a sign of severe pain due to injury, etc. It is best to observe respiration rate before disturbing the animal, as the stress of being caught will naturally increase the count. The easiest way to determine the respiration rate is to watch the animal’s abdomen and count each complete breath cycle.
Respiration rate will be high in healthy animals that have been running, are stressed, or exposed to high ambient temperatures.
Palpation to check
1- Different organs and tissues
2- Colour of mucus membranes (tissue around eyes and gums). Pale or bluish membranes indicate internal bleeding or poisoning.
Confirmatory Diagnosis
This mainly lab diagnosis:
Tentative diagnosis will let you to choose the appropriate lab. method for confirmatory diagnosis;
Laboratory techniques used for diagnosis
Mainly depends on samples send to the lab. So appropriate sample selection, collection and processing will be the key for accurate diagnosis and it will influence lab efficiency.
General sample selection and collection guidelines should include the followings:
1- Select the correct sample and collect the specimen by the proper technique and the proper supplies.
2- Collect adequate volumes. Insufficient material may yield false results.
3- Place the specimen in the container design to promote the efficiency of the sample and to eliminate leakage and potential safety hazards.
4-label each container with full information (date, site, other observation could be with accompanied sheet)
5- Appropriate device and method of collection.
6-Avoid chemical or microbial contamination when ever is possible to ensure the sample representatives of the condition.
(A) Techniques used for diagnosis of non infectious diseases
Sample mainly body fluids (blood, urine, milk, CSF)
(B) Techniques used for diagnosis of infectious diseases
1-Microscopic examination
could by :
(i) Direct smear (wet)
(ii) Stained smear
*What is usefulness of direct smear? QUICK
*Can be done at the site of sample collection
2-Isolation and identification of the causative agent
Methods of isolation depend on the type of organism, bacteria , virus, fungus, etc..
The isolation and identification is considered as one of the most confirmatory diagnostic method
It take time and need sophistication, lab facilities
3- Immunoassay
Analytical methods that incorporate Ags or Abs to determine the presence of their corresponding (Ags or Abs) in a variety of media (eg body fluids, tissues)
It determinate Abs that produced in response to some nonself protein or Ags ( constituent of organism that have antigenic properties).
The term serology (serologic or serodiagnosis) is detection of Abs in the serum. Some times the term could be used when the media is not serum eg saliva or milk as long as the Abs or Ags are detected.
Hence the term serologic assay can be considered essentially synonymous with the term immunoassay.
Purposes and uses of serological tests
1-Particularly valuable in diagnosis infection when it is difficult to culture and dangerous to handle.
2-The most common uses is to identify infection and differentiate between acute from past infection (types of Ab with clinical data).
3-Assessment of diseases progress and understand kinetic of immune response.
Specific immunoassays for the detection and diagnosis of infectious diseases
1-Agglutination
2-Precipitation
3-CF
4-Radioimmunoassay
ELISA
Most popular and revolutionized immunoassay. Easy to perform and adapted to test large number on samples and do need the use or radioactive substances and also determine the class of Ab.
4-Molecular diagnosis
Three terms, genetics (genetic engineering), molecular biology and biotechnology are used in field of diagnosis (what these terms mean)
Molecular biology now commonly used in the diagnosis of infectious diseases and non infectious diseases (eg. genetic disorders) (how)
Many molecular techniques are used in diagnosis of infectious diseases
Molecular techniques
1- Polymerase Chain Reaction (PCR)
Polymerase chain reaction is the test tube system for DNA replication that allows a “target” DNA sequence to be selectively amplified many folds in just a few hours
During PCR, high temperature is used to separate the DNA molecules into single strand, and synthetic sequence of single-stranded DNA (20-30 nucleotides) serve as primers.
Two different primer sequences are used to bracket the target region to be amplified. One primer is complementary to DNA strand at the beginning of the target region; a second primer is complementary to a sequence on the opposite DNA strand at the end of the target region.
To perform a PCR reaction, a small quantity of the target DNA is added to a test tube with a buffer solution containing DNA polymerase, oligonucleotide primers, the four deoxynucleotide building blocks of DNA, and the cofactor MgCl2.
The PCR mixture is taken through replication cycles consisting of temperatures and time periods.
It is necessary to standardize the PCR steps (time and temperatures). This standardization depends mainly on the purpose and nature of the test.
The temperatures and duration of the PCR cycles are controlled by automated thermocycler.
The reaction tubes used in PCR are thin walled straight sides, which ease the heat transfer from the thermocycler to the reaction mixture.
Strategies are required to standardize reaction reagents and to avoid cross contamination.
The PCR is a sensitive, specific and rapid technique, which has been successfully applied to diagnose disease and study genetic disorders.
The assay could detect several microorganisms in a variety of specimens, including sputum, serum, cerebral fluid, urine, feces, and various tissues
Types of PCR
1-Random Amplified Polymorphic DNA (RAPD) PCR
2-RT-PCR
Reverse transcriptase was developed to amplify RNA target (RNA). So first DNA is produced form RNA by reverse transcription and the DNA is amplified. Using RT enzyme.
3-Nested PC
It was developed to increase the sensitivity and the specificity of PCR
It uses two pairs of amplification primers and two round of PCR.
One primer is used the first round for 15-30 cycles and the product of the first cycle was then subjected to the second round of amplification with second set of primers that anneal to sequence internal to the sequence of first primer.
4-Multiplex PCR
Two or more primer sets designed for amplification of different targets are included in the same reaction mixture
By this technique, more than one target sequence in a clinical sample can be co amplified in single tube.
The primers used must be carefully selected due to difference in annealing temps. And should lack complementary.
it is less sensitive
Restriction Endonuclease Analysis (REA)
This method consists of extraction of DNA from homogenous population of organisms, digestion of the DNA with a restriction endonuclease enzyme, and electrophoresis of the digested DNA in an agarose gel.
The restriction endonuclease recognizes and cleaves double-stranded DNA at specific 4 or 6 base-pair sequences and a set of fragments is generated. The migration of these fragments in agarose gel is related to molecular weight; a pattern of bands is produced that can be seen by ultraviolet light if stained with ethidium bromide. This pattern constitutes a characteristic “fingerprint” for a particular DNA.
Types of it RFLP
DNA Hybridization
Hybridization allows specific DNA sequences to be analyzed against the complex background of eukaryotic genome.
To focus on an individual genome, DNA from the target organism is isolated, fragmented with restriction enzymes, and separated by gel electrophoresis.
The DNA fragments are denatured to render them single strand and exposed to a solution containing radioactive DNA “probe.”
The probe consisted of single-stranded nucleic acid (either DNA or RNA) with a sequence chosen to a base pair with the gene of interest.
Under appropriate conditions of temperature, salt, and pH, called “stringency,” the probe will bind to its corresponding sequence in the target DNA.
The presence of a radioactive signal indicates position of the probe binding.
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