VM577 Vaccine Information Exercise
Version 3.1 1/10/08 Updated January 20, 2010
The following is intended to provide guidance for going about determining the economic benefit of using a leptospirosis vaccine (Leptospira borgpetersenii serovar hardjo (Type: hardjo-bovis) ) as a component to control bovine leptospirosis in a cattle herd.
You are welcome to work in groups of several students each - multiple minds are better than one and it spreads the work around. Decide whether your herd of interest is a grazing beef herd or a housed dairy herd. The first draft of your report is due in 2 weeks.
Vaccination Programs:(modified from a presentation to livestock producers)
One size does not fit all!
Establishing a vaccination program for a herd requires consideration of complex issues. To quote Brand et al. (1996): "A vaccination program must be based on the disease status of the herd, reproductive status of youngstock and cows, potential interference by maternally derived antibodies, potential effects of vaccine-induced titers on suitability for export or introduction into bull studs, whether the herd is open or closed, prevailing farm and area conditions, national or regional vaccination strategies, the possible advantageous/disadvantageous post-vaccination sequalae, and the cost benefit ratio of a vaccination program (emphasis mine). Furthermore, the vaccination schedule should be known, as well as the antigenic form of vaccine to be used (inactivated, modified live, live, or deletion vaccine), route of administration (intramuscularly, subcutaneously, or intranasally), and whether a booster vaccination is needed and when." Because the immune system requires time to respond to vaccines, the final dose should be given sufficiently in advance that the animal can be fully protected when the exposure or stress occurs. Vaccines requiring priming doses must be given sufficiently ahead of the second dose for the second dose to stimulate adequate protection. Failure to follow the administration instructions in this regard is a common error that markedly reduces vaccine efficacy.
Many vaccines are likely only marginally beneficial, biological and economically.
Some vaccines, such as the oil adjuvant vibrio (Campylobacter fetus) and the muscle clostridial toxoids (e.g., Clostridium chauvoei (blackleg), Cl. Septicum (malignant edema)), are highly efficacious. At the other end of the spectrum are the older Pasteurella whole cell bacterins that don't contain leucotoxoids as some evidence suggests that they actually increase the severity of bovine respiratory disease under some circumstances. Others fall in between. For example, a controlled study of the trichomoniasis vaccine showed that 63% of vaccinated heifers delivered calves while only 32% of the controls did so and the vaccinates were culture positive for 3.8 weeks while controls were for 5.4 weeks (Kvasnicka Am J Vet Res 53:2023(1992)). Although the vaccine improved the situation, it certainly didn't prevent the problem. Other control measures such as rigorous testing of young bulls, culling of older bulls and late calvers may be more beneficial economically. Some vaccines such as leptospirosis are considerably more effective against non-host adapted strains than host-adapted strains. A general rule of thumb is that if a natural infection after birth results in a chronic carrier animal, which means that that animal's immune system was not able to eliminate the infection, then vaccination of that animal isn't going to stimulate the immune system sufficiently to prevent infection either. Thus, a general conclusion is that many vaccines will reduce the number of animals infected, will reduce the proportion of those that become clinical cases among those that are infected and will reduce the amount and duration of shedding in those that are infected. But for many diseases vaccination will not completely prevent the problem and other control measures may be equally or more important. Unfortunately, it is human nature to look for the single magic bullet that can be given once and forgotten.
The evidence from sound studies of a positive economic benefit from the use of many vaccines across large numbers of herds is lacking. The lack of sound evidence doesn't necessarily mean that the cost-benefit isn't positive. Anecdotal evidence suggests that the severe clinical outbreaks of Type II BVD tended to occur in herds that were not properly vaccinated for BVD. For bovine respiratory disease, about half of the studies indicate equivocal benefit while half indicate marginal benefit of use in calves prior to weaning. As noted in the pneumonia example above, their use clearly doesn't completely prevent the problem. To get the needed evidence of benefit, producers need to make the evidence from sound randomized, multi-herd, concurrent controlled, blinded field trials a condition of purchase.
USDA vaccine licensing does not require evidence of efficacy in cattle under normal farm and ranch conditions and only requires evidence of efficacy against specific aspects of the disease.
The USDA provides minimal monitoring of vaccines for safety, purity, potency and efficacy, concentrating primarily on safety and purity (freedom from other infectious agents or toxic materials). This is done by monitoring the procedures and sanitation in the plants producing the product. To show efficacy of vaccines the manufacturer performs laboratory challenge of specially selected animals rather than using controlled field studies of vaccine efficacy under actual use conditions. Espeseth and Greenberg with the USDA Center for Veterinary Biologics wrote "It is generally more difficult to demonstrate significant efficacy under field conditions. Field efficacy studies are often inconclusive because of uncontrollable outside influences." Further, if other sound, independent evidence shows that a USDA-approved product is not efficacious under most circumstances, the law does not prevent its production or sale. Thus, a USDA-approved and licensed product may not be efficacious under the under field conditions. Further, the aspect of the disease against which efficacy must be demonstrated is quite specific. For example, for the BVD vaccines evidence of efficacy against the clinical gastointestinal disease syndrome is required but efficacy against fetal infection, which is essential for preventing the persistent carrier state and the most important component for control of BVD in breeding herds, is not unless it is a specific label claim.
For on-line information on USDA vaccine licensing policies, see USDA Center for Veterinary Biologics
Finally, vaccine administration errors can render the best designed program ineffective. Cattle must be capable of responding to the vaccination. Improper handling and disinfectant residues can kill MLV vaccines. Improper delivery can fail to deliver an sufficient antigen mass. Bad management overwhelms the best vaccine every time (CA Hjerpe).
Vaccine Program Recommendations
I recommend that in concert with their herd veterinarian, producers design a vaccination program for the specific circumstances of their herd. Without knowledge of the herd specifics and of the area I'm unwilling to make blanket recommendations. I also suggest that producers put their vaccine requirements out to bid. With the above caveats in mind, the following are on-line vaccine recommendations in title alphabetical order from a number of experts:
- Designing Preventive Health Management Programs for Cattle Producers (Griffin, Perino, Rupp, Hamilton - Nebraska G97-1313-A
- Great Plains Veterinary Education Center
- The "UN-GPVEC" Calf to Feedyard Health Total Outline (doc file) (U Nebraska)
- Immunizations for Oklahoma Cow Herds (L Rice, University of Oklahoma, html)
- Keep Herd Health Simple and Make it Fit the Beef Cattle Operation (EJ Richey, Florida, html pdf)
- Preconditioning Programs: Vaccination, Nutrition, and Management (1999, NDSU AS-1160)
- Preventive Herd Health Program (GL Stokka, Kansas, 1998, EP-50 pdf )
- TAMU Ranch to Rail: Value Added Calf (TexVAC) Vaccination Management Program(33 pg. pdf, short pdf)
Some General Infectious Disease Concepts:(background information)
The Iceberg Principle: With most diseases in a herd, more subclinical (silent) cases occur than clinical cases.
Even in outbreak situations more animals in the affected group have infections and are subclinical or silent cases than there are clinical cases. For most diseases, both infectious and non-infectious, the ratio between clinical cases and subclinical cases is typically 1:5 to 1:20. Under some circumstances, a herd can be widely infected with an infectious agent but few if any clinical cases occur at all. For some infections such as Bovine Leukemia Virus (BLV) the ratio may be 1:100, meaning that clinical cases rarely occur. Many clinical cases are due to infectious agents that are in most herds most of the time but that usually don't cause clinical disease. Thus, the occurrence of clinical cases is an indicator that something is amiss in the management of those animals.
Good explanations of the balance between resistance and disease challenge and fitting these into the beef cow production cycle are those authored by Dr. Ed J. Richey, Univ of Florida Beef Extension veterinarian:
- Keep herd health simple and make it fit the beef cattle operation (1991) (pdf)
- Constructing Diagrams to Represent the Management System of a Beef Herd, Bulletin 278 (html, pdf)
Richey, E, R Hendry, S Cornwell (1992). Herd Health for the Beef Cattle Operation. The Bovine Proceedings 24:156-167.
For more information on the above epidemiologic concepts for disease in animal groups, see:
Epidemiology Concepts for Disease in Animal Groups
Infectious disease problems generally cannot be controlled by focusing solely on the clinically affected animals.
For on-line information on considerations in bovine salmonellosis control, see: Bovine Herd Salmonellosis, Including DT104: Eleven Characteristics to Keep in Mind.
- Because subclinical (silent) cases of most diseases are more numerous than clinical cases in a herd, the economic cost of subclinical disease exceeds that of clinical disease.
- New infectious agents often enter a herd and are unnoticed for some time before clinical disease occurs and a diagnosis is finally made.
- Carriers of subclinical infection are the reason for the old but true saying that "Most disease is bought and paid for!" and are what keep it in a herd.
- Quarantine isolation of purchased animals will not protect a herd against the chronic carriers of many infectious agents!
- Even using the best laboratory tests, subclinical (silent) disease is considerably harder to detect and diagnose than is clinical disease and is more error-prone.
- For many infectious diseases, the single most important piece of information that a purchaser can have is honest, sound knowledge about the status of the herd of origin with respect to the infections of concern.
Work with rather than against "Mother Nature":
- Taking advantage of the opportunities that Mother Nature presents is far less costly and more effective than fighting Mother Nature, which is often a loosing battle.
- Continued success is far more likely if a disease problem is attacked at multiple points rather than attacking it at a single control point.
For example of management practices to reduce calf scours, see A Biocontainment Approach to Calf Scours - The Sandhills Calving System (Dr. David Smith, U Nebraska) in UNL Veterinary Extension Publications: Hot Issues
Other On-line Information Sources:
The Internet contains a wealth of relevant materials, one reason being that a major mission of the agricultural extension service is to communicate information to producers. The Internet provides an excellent mechanism for doing so to the dispersed producer audience. As a result, many very useful extension publications are on the Web. The medical literature can also be searched for free on-line through the National Library of Medicine. Cornell Consultant also provides an on-line means of identifying the most recent relevant clinical literature as selected by Dr. Maurice White, a Cornell food animal clinician.
Cornell Consultant: A Diagnostic Support System for Veterinary Medicine (Dr. M E White)
This is a unique resource to establish differentials and to identify current papers on a disease.
National Library of Medicine PubMed
One of the great features of PubMed is the "related article" function that enables you to find the closely related papers that they have indexed close to a good hit that you have found.
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