ABSTRACT: Serology is used to quantify antibody litres that can be used to indicate the current immune status of an individual and could, therefore, be used to formulate tailored vaccination programmes for individual dogs. Although extended re-vaccination intervals are beneficial in reducing the concept of vaccine overload, not all individuals may be able to mount an immune response lasting for three years and some animals may be able to maintain immunity to core diseases for longer than three years. The two key tests in pre-vaccination serology are virus neutralisation testing and haemagglutination testing, although ELISA based in¬house testing has now been developed.

Despite the biochemical differences between serum and plasma, they both contain antibodies produced in response to antigenic stimulation, such as natural disease or vaccination. Serology is the study of serum and plasma using various techniques to quantify these antibodies, to provide a numeric value, which is referred to as a titre. The titre can be used to indicate the current level of immunity.

Serology can be used as part of rabies vaccination programmes such as the Pet Travel Scheme (PETS). Until recently, serology could only be completed in external laboratories, but now an in-house test has been created by Biogal making the service more accessible and financially viable.1

Serology and vaccination – where is the link?

Extended recommended re-vaccination intervals for vaccines against core diseases have reduced the concept of vaccine overload in dogs 2’3 4 but there is no guarantee that every individual will respond in the same way to vaccination. Some individuals may require more frequent re-vaccination, and some may be able to maintain immunity that exceeds the recommended three-year re-vaccination interval.

The Vaccination Guidelines Group (VGG) of the World Small Animal Veterinary Association supports the use of serology for indicating current immunity to assist in the decision of whether re-vaccination is necessary.3 Pre-vaccination serology is of use for the core diseases – distemper, hepatitis and parvovirus (DHP). This is because immunity to these diseases is humoral – involving antibodies; unlike other diseases, such as leptospirosis, which rely on largely cell-mediated immunity and thus cannot be tested for by assessing antibody levels.4

If routine serology was introduced into vaccination programmes for dogs, it would be necessary to implement a protocol that could be followed. Figure 1 provides a suggested protocol for use in practice.

Figure 1: Suggested serology protocol for

Blood sampling could be undertaken on an annual basis by the veterinary nurse, who could inform owners of the results and arrange an appointment for vaccination by the veterinary surgeon. Numerous problems can be detected at vaccination times and, therefore, it would be wise to complete a comprehensive health check during the blood-sampling consultation, forwarding any problems to the veterinary surgeon for further assessment.

Serological tests and laboratory requirements

The two common tests used for pre vaccination serology in external laboratories demonstrate the biological effects of the virus being investigated. For parvovirus, haemagglutination inhibition testing (HIT) is the test of choice; while for distemper and hepatitis, virus neutralisation testing (VNT) is usually used. The HIT and VNT tests are explained in Figures 2 and 3.

Figure 2: Haemagglutination inhibition testing (HIT!)

Figure 3: Virus neutralisation testing (VNT)

VNT involves examining viral effects on cells and whether the antibodies can neutralise the virus; whereas HIT involves examining the ability of antibodies to inhibit the agglutination, or ‘clumping together’ of red blood cells.5 Both of these tests demonstrate the biological effects of the virus, and are very sensitive and highly specific.6

Practices should send approximately 2ml of serum or plasma in plain tubes to the external laboratory (Dr Paul Burr. Personal Communication. Dr Paul Burr is the chief executive of Biobest Laboratories).

In-house serological testing for re-vaccination

The ImmunComb VacciCheck test is ELISA-based and designed to be completed in the practice.1 Unlike a standard ELISA test, the VacciCheck lends itself to being used in a practice environment as it is easy to use and the results are rapid.1

Although it is a recent introduction, there are good validation data available for the test.7 The tests are reasonably priced too and offer a more financially viable alternative than testing in external laboratories, which inevitably require advanced equipment and highly trained staff.

Advantages of serology

Research has confirmed that there are differences in the way dogs respond to vaccination, especially the effect of breed.68'9'10-11'12

Some breeds of dog are suspected to respond poorly or inappropriately to vaccination. However, there are currently insufficient data to make definite conclusions that all dogs of a certain breed will respond inappropriately, so individual serological assessment provides a means of indicating whether antibody titres are present.

The age of the dog has also been found to affect immune responses to rabies vaccination which may warrant further research into the correlation between age and response to routine vaccination.13 Serology enables vaccine programmes to be tailored to an individual dog, and could help ensure that boosters are only given when they are needed.

Depending on patient co-operation, blood sample collection is relatively easy, and can be undertaken by Listed or Registered Veterinary Nurses as a Schedule 3 procedure (Figure 4).

Figure 4: Blood sampling dogs for serology could be an area of responsibility for Listed or Registered Veterinary Nurses. (Image courtesy of Laura Daniels)

The latest study to show which vaccination protocols are being used in the United Kingdom was completed in 2009 and indicated that 53.5% of veterinary surgeons are re-vaccinating every three years for DHP.14 However, in response to many vaccine manufacturers extending their re-vaccination intervals, this proportion may now be much higher.

Although this protocol change has been recommended on a scientific basis, some owners may wonder why their dog is suddenly not receiving the ‘full vaccine’ that had been given for so many years.

Granted, there will be many owners who see this as beneficial from a cost perspective, but there may be some owners who are cautious about this perceived ‘lack of vaccination’. The results from serology can be used to justify the veterinary surgeon’s clinical decision regarding the necessity of re-vaccination.15

Serology can identify those dogs that require more frequent re-vaccination but may also be used to identify dogs that can maintain immunity for longer, thus reducing unnecessary vaccination administration.

… and the disadvantages

Cost is the main concern, as pre vaccination serology completed in external laboratories costs approximately £45 inclusive of VAT. Combining this with the blood-sampling fee and the vaccination, if required, plus the practice profit margin, is likely to become expensive. Laboratory based testing takes approximately 72 hours owing to the nature of the tests and the incubation times required. This means that owners would have to bring their dog back into the practice for the vaccination if it was needed.

The introduction of in-house testing is beneficial because of its lower costs, and testing and re-vaccination can be completed in one trip.

As serology cannot quantify cell- mediated responses, it is possible that some dogs may have sufficient cell-mediated immunity to provide protection from infection, but
have non-protective antibody titres. They may, therefore, be re-vaccinated when they do not need it. Clearly, this defeats the objective of serological testing; but as only leptospirosis relies on cell-mediated immunity the effect is less significant.

Results can only demonstrate antibody titres at that one particular moment in time.15 It is currently impossible to predict antibody titres for any forthcoming period for the individual animal, although one study found no significant antibody decrease over time.16

Currently there is no specified time interval for serological testing to be repeated to continually assess antibody titres. However, some authors recommend that testing should be completed annually, although more research is needed into antibody decay.

Conclusion

Serology can be a useful tool in deciding whether a dog requires re-vaccination, and the introduction of in-house testing allows for a more accessible, financially viable service. For dogs that are suspected of having reduced immune responses – especially those on extended vaccination programmes for core diseases – serology could be a useful part of the risk/benefit decision made by the veterinary surgeon.

Serology could also be introduced to ensure optimum protection and to indicate a successful immune response post vaccination.

Finally, its use can be recommended to owners who are concerned about under- or over-vaccination of their pet. As well as the potential benefits of this approach to preventive health care, the routine use of serological testing may enable the veterinary nurse to play a more active role in vaccination by being responsible for sampling and testing. 

Author

Bethaney Heayns BSc(Hons) RVN

Bethaney Heayns qualified as a RVN in 2008 and graduated with a First Class Honours Degree from Harper Adams in 2009. This article was completed when Bethaney worked as a research assistant at Harper Adams. She is now based at the Royal Veterinary College as a clinical investigation nurse.

To cite this article use either

DOI: 10.1111/j.2045-0648.2012.00171.x or Veterinary Nursing Journal Vol 27 pp 190-193

References

1. BIOGAL GALED LABS. [2011] What is Biogal's ImmunoComb? (online). Available Irom: http://www.biogal.co.il/biogal/Producls/Technology/ 

2.  SCHULTZ, R. D. (2006) Duration of immunity for canine and feline vaccines: a review. Veterinary Microbiology (1711): 75-79.

3.   VGG (2010) Guidelines for the vaccination of dogs and cats compiled by the Vaccination Guidelines Group (VGG) of the World Small Animal Veterinary Association (WSAVA) [online] Available from: http://www.wsava.org/PDF/Misc/ VaccinationGuidelines2010.pdf

4.   B0HM. M. (2009) Current vaccination strategies in dogs and cats In Practice 31: 2-7

5.   BURR. P. and SNODGRASS. D (2004) Demystifying diagnostic testing: serology. In Practice 26(9): 498-502.

6.   TIZARD. I. R (2009) Veterinary Immunology. An introduction. Missouri: Elsevier Mosby

7.   MAZAR. S.. LARSON. L. and LAVI. Y. (2009) Sensitivity-specificity-accuracy and difference between positive and negative mean results of the ImmunoComb® Canine VacciCheck Antibody Test Kit for Canine Distemper, Parvo and Adenovirus (Online) (Unpublished datal Available lrom:hltp://www.biogal.co.il/uploads/contents/do cuments/pdf/Articles/Study-CanmeVacciCheckKit pdf

8.   F0ALE, R D . HERRTAGE. M E.. and DAY, M. J. (2003) Retrospective study of 25 young Weimeraners with low serum immunoglobulin concentrations and inflammatory disease. Veterinary Record 153: 553-558.

9.   STRASSER. A.. MAY, B.. TELTSCHER. A . WISTRELA. E. and NIEDERMULLER. H (2003) Immune modulation following immunization with polyvalent vaccines on dogs Veterinary Immunology and Immunopathology 94: 113-121

10.   DAY, M J (1999) Possible immunodeficiency in related Rottweiler dogs. Journal of Small Animal Practice 40 561-568.

11.   DAY, M. J. (2008) Vaccination. In: Clinical Immunology of the dog and cat. Ed M. J. Day London: Manson Publishing Ltd 424-427.

12. COYNE. M J.. BURR. J. H. H.. YULE. T. D.. HARDING. M. J.. TRESNAN, D B and McGAVIN. D. [2001] Duration of immunity in dogs after vaccination or naturally acquired infection Veterinary Record 149(17): 509-515.

13 MANSFIELD. K L. BURR. P. D . SNODGRASS. D. R.. SAYERS. R.. and FOOKS. A. R. (2004) Factors affecting the serological response to dogs and cats to rabies vaccination. Veterinary Record 154(14):423-426

14.   HEAYNS, B. and BAUGH. S. 120101 To revaccmate or not to revaccmate: Does serology have the answer for canine re-vaccination 7 Proceedings of the 53rd BSAVA Congress. April 8th-10th. 414

15.   BURR. P. [2006] Serology – An alternative to boosters 7 Veterinary Microbiology 117(1): 39-42

16.   OTTIGER. H-P. NEIMEIER-FORSTER. M . STARK. K D C . DUCHOW. K.. and BRUCKNER. L. (2006) Serological responses of adult dogs to re- vaccmation against distemper, parvovirus and rabies. Veterinary Record 159(1): 7-12.

Further reading

BIOBEST LABORATORIES (2009) Techniques. (Online) Available from: http://www biobest.co.uk/diagnostics/techniques.html

DAY. M J (2011) Vaccination of dogs and cats: no longer so controversial? Veterinary Record 168: 480-482

Veterinary Nursing Journal • VOL 27 • May 2012 •