The Moredun Foundation News Sheet Vol. 3, No.17 Clostridial Diseases of Sheep (Published November 2002) Colin Macaldowie BVMS PhD MRCVS Moredun Research Institute Pentlands Science Park Bush Loan, Penicuik Midlothian EH26 0PZ
Highlights Clostridial infections of sheep have been recognised for over 200 years as a cause of rapidly fatal disease. Clostridial infections progress rapidly and many sheep may be found either dead or dying. Intensive treatment with antibiotics is rarely effective. Clostridial bacteria are ubiquitous and produce spores, which persist for long periods in soil making some pastures particularly hazardous. Disease outbreaks precipitated are by trigger factors, ranging from changes in management, to parasitic activity and traumatic damage to organs. Vaccines are readily available and ensure effective protection against most forms of clostridial disease encountered in the UK. TWO injections at least 4-6 weeks apart are required. Vaccinated animals, including adults, require booster injections every 12 months. Breeding ewes should be vaccinated 4 weeks before lambing to ensure their colostrum contains high levels of antibodies to protect the newborn lamb. Breeding ewes should be vaccinated 4 weeks before lambing to ensure their colostrum contains high levels of antibodies to protect the newborn lamb. Failure to vaccinate raise concerns that losses due to clostridial disease will once again reach the unacceptably high levels seen up until the early part of the 20 th century. 2
Introduction Clostridial diseases of sheep have been recognised clinically for over 200 years. However, it was not until the end of the 19 th century that it was appreciated that bacteria producing powerful toxins (Table 1) caused them. Recognition of the different clostridial types and ways of combating them continued throughout the 20 th century and was the primary reason why farmers founded the nimal Diseases Research ssociation (DR) which established the Moredun Research Institute in the 1920s. t that time, large numbers of lambs were dying from lamb dysentery caused by neonatal infection with what we now know to be Clostridium perfringens type B. Veterinary scientists at DR isolated the bacteria responsible and soon developed the first effective vaccine against the infection. Work on the other sheep clostridial diseases quickly followed and their associated vaccines became forerunners of the commercial vaccines available today. Clostridial bacteria are Gram-positive anaerobic rod-shaped bacilli. They vary from 3-10 µm in length and from 0.5-1.5 µm in width and all have the ability to form exceptionally tough structures known as spores that allow them to survive for many years and remain a risk to unvaccinated sheep. The bacteria and spores are ubiquitous in the environment and are particularly associated with the soil. They are also often found in small numbers in normal individuals where they are harmless until some trigger factor causes them to grow and multiply and produce powerful toxins. Occasionally they also invade other tissues. Common trigger factors include sudden changes in management or diet, traumatic injuries, particularly those causing bruising or penetrating wounds and parasitic activity from intestinal worms or liver fluke. Usually the course of disease is so rapid that animals are found moribund or dead before treatment can be given, but with certain infections such as tetanus or botulism the animal may survive for several days. Types of Clostridial Disease Clostridial disease in sheep can be broadly classified into 3 categories according to the systems or organs involved: () Those affecting the alimentary system (enterotoxaemias) and internal organs through the release of toxins (B) Those causing muscle damage or gangrene (myonecrosis) and the circulation of clostridial toxins in the blood (toxaemia) (C) Those causing nervous damage (neurotropic disorders) The common forms of clostridial encountered in the UK, the clostridial species that cause them, the ages of animals affected and the clinical symptoms are summarised in Table 1. 3
4 Table 1. Common forms of Sheep Clostridial Disease found in the UK, =Enterotoxaemia, B=Myonecrosis with toxaemia, C= Neurotropic Disease Organism (s) nimals affected & predisposing factors Category Symptoms & Comments Lamb dysentery Struck Pulpy kidney Type B type C type D Lambs from a few days up to 3 weeks old, associated with poor hygiene at lambing. Young adults of one to two years and lambs at pasture, may be associated with concurrent fluke infestation and sudden changes to diet. ny age but usually lambs 6 weeks to one year, associated with sudden diet changes. Stomach pain, anorexia (off food), may develop bloodstained scour, collapse, death from 2 hours 3 days after onset. bdominal pain, lethargy, convulsions. nimals usually found dead. taxia (staggering), collapse, convulsions, sudden death usually within 2 hours of onset. Widespread and common. Braxy C. septicum Young sheep in their first autumn and winter, associated with eating frosted forage causing subsequent inflammation of the stomach (abomasitis). Black disease Bacillary haemoglobinuria (bacterial redwater) C. novyi type B C. haemolyticum (C. novyi type D) dult sheep and older lambs. Bacteria found in normal liver. Commonest trigger factor is concurrent fluke infestation. dult sheep. Bacteria found in normal liver. Trigger factors include fluke infestation and tapeworm oncospheres migrating through the liver. Lethargy, separation from flock, collapse, coma, sudden death. nimals usually found dead. Lethargy, recumbancy, rapid breathing, sudden quiet death. Darkened areas of skin develop rapidly post mortem giving the disease its name. norexia, dark urine, sudden death. Treatment of sheep dogs for tapeworm (T. hydatigena) will help to reduce incidence. Not common. bomasitis and toxaemia C. sordelli ll age groups. ssociated with intensive creep feeding of lambs and sudden changes of diet in older animals. Lethargy, separation from flock, bloat, recumbancy, sudden death. bomasitis (inflammation of the 4 th stomach or abomasum) usually occurs in lambs and toxaemia in older animals. Displacement and distension of the abomasum is a consistent post mortem finding. Blackleg (Blackquarter) C. chauvoei ny age, associated with shearing wounds and exposure to C. chauvoei spores in soil contaminated forage. Spores cross the intestine and lodge in muscles. Trigger factors for bacterial growth are unknown B Stiffness, fever, recumbancy, death. Rapid bloating and decomposition of the carcass occurs after death. Characteristic gelatinous changes to affected tissues seen post mortem.
5 5 Table 1 continued. Common forms of Sheep Clostridial Disease found in the UK, =Enterotoxaemia, B=Myonecrosis with toxaemia, C=Neurotropic Disease Organism (s) nimals affected & predisposing factors Category Symptoms & Comments Gangrenous metritis & navel ill C. chauveoi Post lambing ewes and lambs. ssociated with poor hygiene at assisted lambings and not treating lamb navel with iodine B Sanguinous (bloodstained) vulval discharge, anorexia, recumbancy and death. Rapid death in lambs. Rapid bloating and decomposition of the carcass occurs soon after death. Big head or Malignant oedema C. septicum C. novyi C. chauvoei C. sordelli ny age, especially rams. ssociated with infected fight wounds and deep intramuscular injections given using contaminated syringe needles. B Initial swelling under the eyes followed by swelling of the head and upper neck, fever, lethargy, anorexia, and rapid death. Intensive antibiotic treatment in the very early stages of the disease may save the animal but usually results in a slow recovery and permanent disfigurement. Tetanus C. tetani ny age but mainly suckling lambs. ssociated with infected tailing, castration and shearing wounds. Older animals may develop infection from penetrating wounds contaminated with soil. C Stiffness, head back, ataxia, anorexia due to dysphagia (difficulty swallowing), convulsions. Death usually occurs 4-7 days after onset due to respiratory failure. Occasional outbreaks involving large numbers of lambs may occur if tailing or castration is done in unhygienic conditions. Infections in older animals usually sporadic. Botulism C. botulinum type C and D Rarer in UK but any age. ssociated with grazing animals on pasture top dressed with poultry litter and feeding of rodent contaminated, poorly fermented big bale silage. May also occur under drought conditions where sheep are forced to forage on bare pastures C Stiffness, ataxia, excitability and head-bobbing followed by salivation, nasal discharge, breathing difficulties and rapid death Focal symmetrical encephalomalacia (FSE) type D Suckling and weaned lambs also occasionally adults. Bacteria found naturally in intestine. form of pulpy kidney disease with characteristic brain damage. Often occurs alongside cases of pulpy kidney C Lethargy, anorexia, separation from flock followed by ataxia and recumbancy, convulsions, coma and death. Outbreaks in weaned lambs and adults associated with sudden change to carbohydrate rich diet and movement to fresh pasture. Usually only a few animals will be affected.
Clostridial Vaccines Clostridial diseases are supreme candidates for control by vaccination. The ubiquitous nature of the bacteria and spores, including their presence of bacteria in normal healthy individuals, the speed at which clinical disease develops and the unpredictability of disease outbreaks all combine to ensure that prevention by vaccination is the only practical way to reduce mortality. Good management also helps to reduce the likehood of trigger factors associated with disease. However, even the best management systems on their own will not always prevent disease in unvaccinated animals, rather they will allow vaccine(s) to be more effective. Fortunately toxoids (inactivated toxins) are ideal for inclusion in vaccine preparations as they stimulate good protection and are harmless to both sheep and humans. Whilst single toxoid (monovalent) vaccines can be used for specific conditions there has been an increasing tendency for drug companies to produce polyvalent vaccines containing up to 8 clostridial components. Table 2 summarises some of the clostridial vaccine products currently available in the UK. There is, at present very little difference in the cost per dose between the 3 (Lambivac) and 4 (Ovivac) component vaccines and the 7 (Heptavac & Covexin) or 8 (Covexin 8) component vaccines so it seems sensible to use the latter to provide comprehensive protection against the various forms of disease. More recently some products have also included another Moredun discovery in the form of ironregulated protein (IRP) antigens from Mannheimia (Pasteurella) haemolytica and Pasteurella trehalosi to provide protection against pneumonic and systemic pasteurellosis. Clostridial Vaccination Clostridial vaccines contain inactivated components, so two vaccine doses given 4-6 weeks apart are always required to given a minimum protective response in susceptible animals. This is frequently referred to as the primary course. ntibody levels wane over the period of a year and annual revaccination of all stock, including rams, using a single booster dose is always required to maintain immunity. It is important to remember that animals can become fully susceptible if booster injections are delayed meaning they will require another two dose primary course of injections to regain their immunity. On farms where particular diseases are known to occur at certain times of the year, such as pulpy kidney disease in lambs in the autumn or black disease associated with fluke migration in the winter, it may also be advisable to give additional booster injections 4 weeks before problems might be anticipated to occur. Breeding ewes & Ewe Replacements In breeding sheep, booster vaccinations are best administered 2-4 weeks before lambing to maximise protection to the lambs via passive transfer of maternal antibodies present in the colostrum. If ewe replacements are not bred until they are 18 months of age they will also require an additional booster injection at approximately 12 months of age to maintain protection until their pre-lambing vaccination. Lambs Maternal clostridial antibodies in colostrum of vaccinated ewes will provide passive protection of lambs in the first 3 months of life providing they ingest sufficient colostrum (ie. at least 200mls colostrum per kg bodyweight in the first 18 hours of life). Thereafter, all lambs must receive a primary vaccination course starting at 2-3 months of age with the second injection given 4-6 weeks later. Lambs fed colostrum from unvaccinated ewes will require primary vaccination in the first 1-2 weeks of life, but will remain at risk until they acquire full immunity approximately one week after they receive their second injection. 6
Purchased stock Clostridial vaccination should be considered as part of an essential quarantine management programme for purchased stock which would also aim to prevent the importation and spread of other infectious diseases such abortion, lameness, scab and anthelmintic resistant worms. Unless the seller can provide good documentation of previous clostridial vaccinations, it is always safer to assume that all purchased replacements are insufficiently vaccinated on arrival. To protect both themselves and other stock, these animals should receive a full primary vaccination course before mixing with other animals. s with all vaccines, clostridial vaccines do not perform well if given to animals that are suffering from stress. For this reason it is usually worth delaying the start of vaccination until 3-5 days after they have been transported to allow the immune system to return to normal. Table 2. Clostridial vaccine and antiserum products currently available in the UK. Product Components Diseases covered Comments Vaccines Toxoid/bacteria Lambivac Types B, C &D C. tetani Ovivac type D C. septicum C.tetani C. chauvoei Ovivac P Plus s for Ovivac plus: Pasteurella IRP antigens Heptavac Covexin 7 Heptavac P Plus Covexin 8 Tetanus toxoid concentrated ntiserum Tetanus antitoxin Types B, C &D C. tetani C. septicum C. novyi Type B C. chauvoei s for Heptavac plus: Pasteurella IRP antigens s for Covexin 7 plus: C.haemolyticum (C. noyyi Type D) Lamb dysentery Pulpy Kidney Tetanus Pulpy kidney Braxy Blackleg Tetanus s above plus: Pneumonic and systemic pasteurellosis Lamb dysentery Pulpy kidney Tetanus Struck Braxy Blackleg Gangrenous metritis & navel ill s above plus: Pneumonic and systemic pasteurellosis s for Covexin 7 plus: Bacillary haemoglobinuria Provides minimal protection against 3 major lamb killers ctive immunisation of sheep and lambs against 4 of the commonest clostridial diseases For use where pasteurellosis is also known to be a problem. Comprehensive 7 in 1 vaccines for active immunisation of sheep and lambs against the major clostridial diseases. Currently no more expensive per dose than Lambivac or Ovivac For use where pasteurellosis is also known to be a problem. dditional protection against bacterial redwater which may be fluke-associated C. tetani Tetanus Monovalent vaccine for use where tetanus is known to be a problem Hyperimmune serum to C. tetani toxins Tetanus Passive immunisation against tetanus. May be of use in treatment of tetanus cases. 7
Tetanus ntiserum On veterinary advice, antiserum to C. Tetani toxin may occasionally be used to give immediate temporary protection where risk of infection is likely to be high, either as a result of wound contamination, as a preoperative precaution, or as a treatment for animals already affected with tetanus (Table 2). The antiserum is injected into the animal to provide an immediate reservoir of circulating antitoxin to block the effects of tetanus toxins on the nerves. However it is important to stress that this is usually used as an emergency procedure where risk of infection is known to be high and should not be regarded a routine alternative to vaccination. Conclusions The risk of clostridial disease is ever present as the bacteria are found wherever sheep are kept. However frequency of disease can be minimised using vaccines that have proved their worth for almost eighty years and are still completely effective. Further benefits of disease prevention by vaccination also include reducing the amount of bacteria and spores released from infected carcasses thereby making the environment safer for sheep. Despite this it would appear that the recorded incidence of both pulpy kidney and lamb dysentery is again on the increase. Whether this is for perceived economic reasons leading to farmers to stop using vaccines or, worse still, due to improper use of the products available is unclear. However, it should always be remembered that saving even one lamb from disease will pay for many doses of vaccine, whilst not adhering strictly to the recommended doses and frequency of vaccination is a waste of both time and money. nother possible reason for the increase is the current trend towards organic production, which discourages the use of all prophylactic treatments, including clostridial vaccines, until such times as disease occurs. Given the ubiquitous presence and unpredictable behaviour of this particular pathogen, such an approach raises concerns that clostridial diseases may again reach the unacceptably high levels seen before the early part of the 20th century with many pastures once again becoming dangerously contaminated with long-living clostridial spores. Produced by: The Moredun Foundation Pentlands Science Park Bush Loan Penicuik EH26 0PZ Scotland Phone: +44 (0)131 445 5111 Fax: +44 (0)131 445 6235 e-mail: info@moredun.org.uk website: www.moredun.org.uk Moredun 2002. ll rights reserved. No part of this publication may be reproduced or transmitted in any form or in any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the publisher. 8 3