Why vaccinate? Vaccination is the key to preventing some of the most serious sheep diseases. Vaccination stimulates the body’s defence system to build immunity to a particular disease, by exposing sheep to either the live organism presented in a safe form (e.g. Scabby Mouth vaccine) or to a killed organism (e.g. Blackleg vaccine) or to an inactivated organism (e.g. Johne’s disease vaccine) or to part of an organism (e.g. footrot vaccine, most Clostridia vaccines). Indeed, without effective vaccines, the control, prevention and management of many diseases in the large vulnerable populations that make up sheep flocks would be virtually impossible. So what vaccines are available, how are they used and what are the diseases that they protect sheep against?
The Clostridia Diseases The most widely used vaccine in Australia is a vaccine called ‘5 in 1’. It is used to control a group of potentially severe diseases caused by several different species of a bacterium called Clostridium. The important thing to remember with the Clostridia diseases is that they are not something that is caught. The organisms are either in the soil or in the sheep’s bowel. Sheep are therefore exposed to them or already have them in their system virtually all the time. It is only when some trigger compromises the ability of the sheep to resist disease that the sheep become sick. When the sheep become compromised, these bacteria produce potent toxins that cause severe disease and often kill the sheep within hours. There are six diseases that are caused by Clostridium bacteria for which vaccines are available. These are:-
1/Pulpy kidney Pulpy kidney is caused by a toxin produced by the bacteria Clostridium perfringens type D. The bacteria and the toxins they produce are present in the intestines of normal healthy sheep. The bacteria multiply slowly and are continuously swept out with the droppings so that the number of bacteria and the level of toxins never really build up. However, if there is highly nutritious food in the bowel as occurs if sheep are placed onto lush pastures or fed grain in higher levels than they are used to and the passage along the bowel slows, these bacteria are able to multiply quickly and produce lethal quantities of toxin. The toxin causes extensive damage to blood vessels throughout the body, including those in the kidneys (which makes them “pulpy” as they decompose after death) and also those in the brain. It is damage to the blood vessels in the brain that kills the sheep and is also the reason why they tend to die fairly quickly – often in hours, and also why there is no effective treatment. Essentially, these sheep have multiple “strokes”. The history of feeding lush food and symptoms displayed by the sheep arouse suspicions of this problem and it is confirmed by autopsy examination.
2/Tetanus Tetanus is caused by a toxin produced by the bacterium Clostridium tetani. This bacterium survives in soil as spores wherever livestock are kept. These spores contaminate breaks in the skin such as those that occur with tail docking, grass seed penetration or an injury. Once in the body, if in healthy tissue the spores will sit there harmlessly, sometimes for months. If, however, the tissue is damaged, bruised or dead, the spores germinate, multiply and produce a toxin. The toxin then spreads to the nearest nerves and then to the spine and brain, causing a range of nervous symptoms including muscle spasms and convulsions, which get worse when the animal is disturbed. About 80 % of affected sheep die. Diagnosis is made by the typical symptoms displayed by an affected sheep. If the animal is already dead, an autopsy is done to rule out other diseases with similar symptoms.
3/Black Disease This disease is caused by Clostridium novyi type B bacteria. Spores are found in the soil. The sheep ingests these spores. After they reach the bowel, they penetrate the bowel wall and then are carried in the blood stream to the liver. The spores can sit in a healthy liver for months. If anything damages the liver, the spores in the liver germinate and produce potent toxins. Typically, the liver damage is caused by liver fluke but liver damage due to any cause can trigger the disease. As in tetanus, the toxin damages the blood vessels and death occurs quickly
4/Blackleg In this disease, spores of Clostridium chauvoei get into a sheep’s muscle. Spores are found in soil and the intestines and droppings of healthy sheep. They reach the muscles either through a skin wound or by penetrating the bowel wall and then being carried in the bloodstream. Once in the muscles, they remain inert unless the muscle is damaged. This disease is particularly nasty. Once the muscle is damaged, the spores multiply and release toxins. Affected muscles become dark and gas bubbles develop, which make the areas feel spongy and crackle if touched. Any muscle can be affected –mostly leg muscles but also the heart and even the tongue. Sheep of any age can be affected, including lambs a few days old, which are infected through the navel. Sheep that die of Blackleg contain billions of bacteria that then form spores that not only contaminate the surrounding soil but are also dispersed by wind and rain.
5/Braxy and Malignant Oedema. Braxy is another of the Clostridia diseases. Caused by Clostridium septicum, fortunately this one is rare in Australia. This bacterium is also found in the soil and digestive tract of healthy sheep. Disease occurs when the wall of the abomasum (one of a sheep’s four stomachs) becomes damaged, typically by eating frozen grass. As the bacteria multiply in the wall of the abomasum, they produce a fatal toxin. As with the other clostridial diseases, treatment is unrewarding and often affected sheep are just found dead. C. septicum also causes Malignant Oedema. This disease can be caused by several bacteria but the most common is C. septicum. This bacterium infects wounds or bruised tissue, causing them to discolour and discharge a blood-stained fluid. C. septicum is found in soil and interestingly in the mouths of crows. One of the most common sites of infection are crow-pick wounds. Sheep usually die within 1 to2 days of signs becoming apparent.
Clostridia vaccines Basically, the Clostridia diseases are pretty ghastly. The take-home message is that, by the time the sheep are showing symptoms, they are almost certainly going to die. These diseases are very much diseases of prevention and that prevention is vaccination. The vaccines against these five bacteria are combined into a single vaccine that is called ‘5 in1’.The vaccine contains refined Clostridia toxins and killed C. chauvoei (i.e. Blackleg) organisms. Lambs and adult sheep that have not been vaccinated must initially receive two doses given 4 weeks apart. Following this, annual boosters are given. Often lambs are vaccinated at 4 and 8 weeks of age. It is a good idea to give ewes their annual vaccination 4 weeks before lambing. Vaccinated pregnant ewes will not only be protected themselves but also will pass on immunity to their lambs in the colostrum. Such lambs should be protected for the first 6 to 8 weeks of their lives against these diseases. If adult ewes have not been done, then two shots 4 weeks apart can be given during pregnancy with the second shot being given 4 weeks before lambing. The bottle should be shaken well before use. The dose for a sheep of any size is 1ml and this is given under the skin (subcutaneously). And a good thing is that the vaccine is relatively cheap – 250 doses are about AUD$70.
The 5 in 1 vaccine is sometimes combined with a sixth vaccine against a disease called “cheesy gland” to produce a vaccine called ‘6 in 1’. Cheesy gland is a bacterial infection due to a bacterium called Corynebacterium pseudotuberculosis. This bacterium is found in the soil. Sheep become infected through a break in the skin. Once in the body, the bacteria are carried in the bloodstream and cause abscesses in the lymph nodes and lungs. Infected sheep often show no signs but, when slaughtered, their carcasses are either condemned or of reduced value. The disease is therefore more one of commercial importance rather of sheep health. The vaccination protocol for 6 in 1 is the same as for 5 in 1.
The Clostridial vaccines are available with or without added vitamin B12 and selenium.
Johne’s Disease. Johne’s is the disease that no sheep farmer wants to have. It is an incurable wasting disease. Uncommon 30 years ago, it has now become one of the most prevalent diseases in some areas of Australia. The disease is caused by the microorganism Mycobacteria avium subspecies paratuberculosis. The organism is passed in the droppings of infected sheep. Sheep can become infected at any age by eating pasture or drinking water contaminated with the droppings of infected animals. When ingested during grazing, the bacteria invade the bowel wall, causing thickening and scarring. As this process progresses, the bowel becomes increasingly non- functional, losing its ability to digest food and absorb nutrients. The result is that an infected sheep progressively wastes. Diarrhoea sometimes occurs and in hair breeds, such as the Dorper, a “bottle jaw” becomes visible as a result of fluid developing below the jaw due to the associated hypoproteinaemia (low protein in the blood) . Eventually, animals become too weak to graze and collapse in the paddock and die. There is no treatment.
Control focuses primarily on vaccination. The vaccine will stop sheep that do not have Johne’s from catching the disease in about 95% of cases. If sheep already have the disease, vaccination will not treat them (although if the vaccine is given to sheep that are already infected, it does appear to slow the progression of the disease in some cases). Lambs born into a contaminated environment are vulnerable to infection and the aim is to give the vaccine as young as possible (but old enough for the vaccine to work) and hopefully before the lamb is infected. The recommendation is that lambs are vaccinated as soon as possible after 4 weeks of age. A single vaccination confers life-time immunity. Lambs vaccinated in this way are classified as “approved vaccinates” and can be ear tagged with “approved vaccinate” NLIS ear tags, which are embossed with a large V.
The time to vaccinate against Johne’s is before the disease gets onto the farm. Once there are sick sheep and deaths, many of the sheep will already be infected. The effect on the flock can be catastrophic. If the disease is already on the property, then vaccinating the lambs at 4 weeks of age each year will see a gradual reduction in clinical disease as the older sheep die or are culled and the majority of lambs each year are “approved vaccinates” and develop protective immunity before they come in contact with the disease. There is value in vaccinating sheep that are already infected as the vaccine will slow the progress of the disease and also decrease shedding of the organism in the droppings and therefore property contamination. Eradication of the disease, if indeed this is possible, is likely to take many years, however.
Gudair is Australia’s only vaccine for Johne’s disease. It should be shaken well before use. 1ml is given per sheep, subcutaneously high on the neck just behind and below the base of the ear. As mentioned, a single vaccination confers life-time immunity.
Some sheep will develop a nodular thickening at the inoculation site, which may persist for months. The vaccine is based in a mineral oil and is very irritant if accidentally self- injected by the operator. Care therefore needs to be taken.
Footrot. This was discussed extensively in the August 2020 edition of “Muster”. Footrot is a bacterial infection of the foot caused by the bacterium Dichelobacter nodosus. The primary source of infection is sheep that are carrying the bacteria on their feet. These sheep then contaminate the soil. Dichelobacter survives in soil for 2 to 3 weeks. A number of different serotypes of Dichelobacter occur . Swabs are taken from infected sheep and tested to identify which serotype(s) are present on a property. A property-specific vaccine is then prepared. The vaccine is a purified form of a protein found on the surface of the bacteria. Exposure to this protein stimulates a strong immune response. The vaccine is in a mineral oil base and potentially irritant. It should be shaken before use. Two doses of 1ml are given 4 weeks apart, half way down the neck on the side. Use of the vaccine should be combined with other footrot control measures such as foot baths, quarantining, breeding for genetic resistance and sometimes foot trimming and antibiotic use.
Other vaccines 1/ Eryvac The bacterium Erysipelothrix rhusiopathiae is found in soil and in the bowel of sheep. It can enter wounds and be carried in the bloodstream to joints, where it causes a bacterial arthritis. A number of bacteria can do this but E. rhusiopathiae is one of the common ones. Good hygiene and gentle management that avoids sheep injury decreases the incidence. Outbreaks can occur after dipping where sheep become injured and are forced to swim in a “faecal soup”. If you are concerned, sheep can be vaccinated against this bacterium using Eryvac vaccine. Initially, ewes are given two shots 4 weeks apart; after this, single annual boosters are given. Lambs are protected for the first 6-8 weeks of life if their mothers are vaccinated. The vaccine is recommended in flocks where Erysipelothrix is a problem.
2/ Scabigard Scabby Mouth is caused by a pox-like virus. The virus can persist in soil for years. It needs a break in the skin or mucous membrane (such as those lining the lips and mouth) to gain entry to the body. Pox-like vesicles develop at the site of infection, most commonly around the mouth where the lips have been abraded by eating coarse feed but can occur wherever the skin is broken. The virus runs a natural course of about 3 to 4 weeks. Provided there is no secondary bacterial infection or fly strike, the disease can be allowed to run its course. A scabby mouth vaccine ‘Scabigard’ is available in Australia. The vaccine confers immunity for about 2 years. If vaccinating, it is a good idea to do the lamb drop each year. Vaccination, however, is only recommended in flocks where a scabby mouth problem occurs each year.
After learning about what some of these organisms can do, it almost makes you want to go out and vaccinate your sheep again tomorrow. Vaccination, however, is all about planning. Figure out what diseases you want to vaccinate your sheep against and when they should be done. In this way, you can develop a logical vaccination program that works for your location and management. Vaccination takes time and costs money but when done in an informed way is a vital tool in keeping your sheep healthy. A good general vaccination protocol is to vaccinate all lambs with ‘5 in 1’ at 4 and 8 weeks of age and to give Gudair also at 4 weeks. After this, ‘5 in 1’ can be given annually. In addition to this, if Cheesy Gland, Erysipolothrix or Scabby Mouth is a problem, the sheep can be vaccinated against these diseases. Also, if footrot is a problem, this vaccine should be incorporated into the vaccination program.