Core Vaccine Titer Screen Information

Rabies Titer Test

What do the Micro Rabies Screen Test (MRS) results mean?

The MRS test is a serum neutralization assay based on the RFFIT, designed to provide rapid screening for evaluating the need for rabies boosters. Work done at Kansas State Veterinary Diagnostic Laboratory (KSVDL), at Kansas State University, indicates dogs and cats that have been vaccinated for rabies in the past but are not current on their rabies vaccination status respond similarly to a booster as animals that are current on their rabies vaccination; suggesting that both groups (non-current and current) can be referred to as “pre-exposure” vaccinated animals.

Although revaccinating dogs and cats that have been exposed to rabies is effective for disease management, the challenge is protecting our pets from unknown exposures. For humans at increased risk of rabies exposure, titers are recommended periodically to confirm adequate antibody response to rabies vaccination. The level defined by WHO as an adequate response is 0.5 IU/mL. This titer level is also recognized by OIE as protective in currently vaccinated dogs and cats based on challenge studies.

A review of rabies challenge studies in currently vaccinated dogs and cats indicates that there is a positive correlation between rabies virus neutralizing antibody (RVNA) titers and the level of protection after virus challenge. Previous vaccination, coupled with an RVNA titer of 0.5 IU/mL or higher, is expected to provide the highest assurance of protection.

The MRS test measures Rabies Virus Neutralizing Antibodies (RVNA).

The recognized RVNA level of protection for rabies is 0.5 IU/mL. If the level is below 0.5 IU/mL, a booster may be indicated depending on the pet's rabies exposure risk level. Consult local rabies vaccination laws and regulations for final guidance.

Currently, whether an animal requires a rabies booster vaccination is not determined by the level of RVNA in the serum, but by local regulations, which can vary by interval and the credentials of those who may administer the vaccine. Some states allow exemptions to their rabies vaccine requirement based on the potential to compromise an animal’s health status. Veterinarians are obligated to be familiar with and comply with the legal requirements for vaccine administration. The Compendium of Rabies Prevention and Control recommendations, used as guidance for local regulations, is routinely reviewed in light of new information. Kansas State Veterinary Diagnostic Laboratory is part of this process to influence change that will provide the best guidelines for rabies booster requirements.

References:

Aubert MF. Practical significance of rabies antibodies in cats and dogs. Rev Sci Tech. 1992;11(3):735-60.

Brown CM, Slavinski S, Ettestad P, Sidwa TJ, Sorhage FE. Compendium of Animal Rabies Prevention and Control, 2016. J Am Vet Med Assoc. 2016;248(5):505-17.

Bunn TO, Ridpath HD. The relationship between rabies antibody titers in dogs and cats and protection from challenge. US Department of Health, Education and Welfare, Public Health. 1984(11):43-5.

Moore MC, Davis RD, Kang Q, Vahl CI, Wallace RM, Hanlon CA, et al. Comparison of anamnestic responses to rabies vaccination in dogs and cats with current and out-of-date vaccination status. J Am Vet Med Assoc. 2015;246(2):205-11. Epub 2015/01/03.

Moore SM, A.; Vos, A.; Freuling, C.M.; Ellis, C.; Kliemt, J.; Muller, T. Rabies Virus Antibodies from Oral Vaccination as a Correlate of Protection against Lethal Infection in Wildlife. Tropical Medicine and Infectious Disease. 2017;2(31). Epub 21 July 2017.

 

Viral Serologic Tests

Historically, our profession has considered vaccination a relatively innocuous medical procedure, as evidenced by the fact that in most states, most vaccines can still be purchased over the counter. The standard operating procedures in veterinary practices have been “when in doubt, vaccinate the patient,” believing the benefits of vaccinations always outweigh any possible risks. However, the emerging awareness of acute and chronic adverse reactions to vaccines is changing how vaccine decisions are made in small-animal practices. The current trend is to carefully assess each patient’s disease risk to determine if vaccine(s) are necessary and, if so, which vaccine(s) would be appropriate. The use of serological titers can be a valuable tool in making those vaccine decisions.

Vaccine-induced immunity is a multifaceted process involving antigen processing, humoral immunity, cell-mediated immunity, local immunity and cell memory. Predicting whether a patient is protected against a disease based solely on a single serum titer is a gross oversimplification of this complex immune process. However, despite the drawbacks, the use of serum titers in making logical and informed vaccine–related decisions is gaining popularity, especially in animals with a history of a previous vaccine reaction, in individuals prone to allergic reactions, and in cases where concerns about “over vaccinations” persist.

When interpreting any serum vaccination titer, you must take the following key points into consideration;

• Titer results will vary depending on the laboratory and testing methodology used.
• Even among experts, there is no clear consensus on what titer is considered protective for each disease.
• Titers measure the patient’s immune status at a single point in time and may not necessarily reflect the patient’s future immune status one month or one year later.
• A positive titer will protect against the development of the clinical signs of that disease in the patient; however, it may not prevent the patient from becoming infected or even transmitting the agent.
• Titers only measure circulating humoral antibodies and not cell-mediated immunity, local immunity, cell memory, or the anamnestic response to a viral challenge. Therefore, patients with low titers may in fact be protected.

Serological titers can be useful for determining whether an animal is protected against a specific disease (i.e., a positive or protective titer) at that point in time.

CANINE: There is an excellent correlation between a “positive” titer and protection against viral challenge with canine distemper virus (CDV), canine adenovirus (CAV-2), canine parvovirus 2 (CPV) and Rabies (RV).

CDV: SN > 1: 32
CAV-2: SN > 1: 32
CPV2: HI > 1: 80

FELINE: In cats, there is an excellent correlation between a “positive” titer and protection against challenge with the feline panleukopenia virus (FPL) and rabies virus (RV), but only a good correlation with feline herpesvirus (FHV1) and feline calicivirus (FCV) protection.

FPL: HI > 1: 40
FCV: SN > 1:32
FHV1: SN > 1:16

Serological titers can be used to identify potentially susceptible animals (a negative titer). Because the titer only measures circulating humoral immunity, patients with negative titers may or may not be protected if challenged and, therefore, may be considered possible candidates for re-vaccination.

 

 

References:
AAFP Feline Vaccination Advisory Panel Report: 2013
http://www.catvets.com/guidelines/practice-guidelines/feline-vaccination-guidelines
AAHA Canine Vaccine Guidelines: 2011 https://www.aaha.org/professional/resources/canine_vaccine.aspx#gsc.tab=0
Intervet® website, www.continuum3.com, 2006
Lappin, M.; Use of serologic tests to predict resistance to feline herpesvirus, feline calicivirus, and feline parvovirus infections in cats. JAVMA 2002, vol 220, pgs 38-42.
Mouzin E.; Duration of serologic response to five viral antigens in dogs. JAVMA 2004, vol 224, pgs 55-60.
Mouzin, E.; Duration of serological response to three viral antigens in cats. JAVMA 2004, vol 224, pgs 61-66.
Schultz, R.; Antibody titers – What do they mean? Proceedings of the Western Veterinary Conference 2005, pgs 542-543.
Scott, F.; Long-term immunity in cats with an inactivated trivalent vaccine. AmJVR 1999, vol 60, pgs 652-658
Swan, K.; Leptospirosis Technical Bulletin: Proven Protection After Titers Have Waned. Fort Dodge Animal Health, 2005.
Twark, L. Clinical use of serum parvovirus and distemper virus antibody titers for determining revaccination strategies in healthy dogs. JAVMA 2000, vol 217. pgs 1021–1024.