Vacunas y Geriatría

Life expectancy has been increasing in the last decades in cats and dogs, especially if receiving a good preventive, nutritional and medical care. Senior pets represent now a large percentage of patients in practice and probably will be increasing in the future.

Aging has been defined as a complex process in which the individual suffers from a decline in physical condition, organ, sensory and mental function, as well as immune responses. Obviously, there are important variations (species, dog breeds, and individuals) between biological and chronological age and how the body systems age in each individual, meaning that geriatric abnormalities or diseases may appear earlier or later in pets.

Geriatric medicine has evolved as a new discipline in veterinary medicine leading to the development of specific and deep knowledge on geriatric diseases as well as the development of senior/geriatric preventive health care programs in many practices.

The main goals of a health care program are: first, to address the specific needs of the geriatric healthy cat and dog in terms of prevention and management of disease, nutrition and behaviour, and second, to provide an early diagnosis of age-related diseases, which may have an impact on quality and expectancy of life.

The goal of a health care program in senior pets is achieved with the following criteria.

1.  Increasing frequency of examinations, ideally 6-months intervals.

2.  Routine basic care including ecto and endo parasite prevention, vaccination, retroviral status (in cats), dental care and weight control.

3.  Specific and detailed clinical history about age-related changes (changes on weight, behaviour, habits and activity/mobility).

4.  Systematic physical exam with special attention to geriatric changes (body and muscle condition scores, skin and coat quality, oral cavity, eye and fundus examination, thyroid palpation (cats), heart evaluation, abdominal palpation, spine and join palpation and blood pressure measurement).

5.  Blood (complete blood count, serum biochemistry, total T₄ in cats) and urinalysis to detect diseases in a subclinical stage.

Interestingly, no senior/geriatric health guidelines have given specific vaccination recommendations and refer the reader to different vaccination guidelines (ABCD, AAFP, WSAVA) in which some advises may be found. For instance, in ABCD vaccination guidelines no specific recommendation is given, but says "booster vaccination should be continued in (often elderly) cats with stable medical conditions, such as hyperthyroidism and renal disease".

There is a general lack of knowledge about whether geriatric cats and dogs have special vaccination needs or even is controversial if we should actually address this topic, but we will review existing data.

Immune Function in Senior/Geriatric Cats and Dogs

Aging declines body systems potentially leading to a decrease in immune function (immunosenescence) and/or the presence of a pro-inflammatory state (imflammageing). Moreover, the presence of degenerative, neoplastic or inflammatory/immune-mediated diseases is frequent in geriatric cats and dogs. All those factors might have an impact on susceptibility to infectious diseases and/or causing an abnormal or decreased response after vaccination.

Immunosenescence has been defined as the multifactorial complex of changes that occur in the immune system of elderly individuals that predispose to increased morbidity and mortality to infection and age-related pathology. Immunosenescence occurs in cats and dogs (in theory), making them more susceptible to certain infectious diseases and/or less efficient to mount an immune response after a vaccine administration.

Imflammageing has been defined as the effects of a lifetime constant antigenic challenge and associated production of inflammatory mediators that may trigger the onset of inflammatory disease in older individuals. It has also been shown that it occurs in cats and dogs, but there is no data about its effects on postvaccination immune response.

The following humoral and cellular immunological differences have been shown in senior cats and dogs (and humans) in comparison to adults after several studies:

1.  Decreased number of circulating leucocytes (lymphocytes, CD4+ T cells, CD8+ T cells, B cells, CD56+ NK cells, and eosinophils).

2.  Elevated concentrations of IgM and IgA. Antibodies may have lower affinity for antigens.

3.  Lower levels of insulin-like growth factor (IGF-1) which may be associated to lower numbers of CD4+ T cells.

4.  Reduced blood lymphocyte blastogenic responses to stimulation with several mitogens.

5.  Increased monocyte production of pro-inflammatory cytokines (IL-1beta, IL-6 and IL12p40) tested by mRNA compared with middle age.

Questions may arise about if either immunosenescence or proinflammatory states have an actual impact on immunity which should lead to changes in vaccination protocols in old cats and dogs.

Although no specific studies have been done about the practical consequences of all these immune changes the following conclusions and recommendations can be given:

1.  Studies on duration of immunity (DOI) have shown long-term immunity for core vaccines in dogs and cats having received a proper primovaccination and at least 3 year boosters. There are some experimental evidences that older cats and dogs have a persisting immunological memory (serum antibody levels) to core vaccines which may be readily boosted by a single dose. Moreover, there is no evidence or clinical experience in practice that geriatric cats or dogs (properly vaccinated) suffer from a major incidence of infectious diseases prevented by core vaccines. Based on those three facts it does not seem needed at this point to increase booster frequency (more than every 3 years) for core vaccines.

2.  There is some evidence that older cats and dogs may not respond efficiently to novel antigens that they are administered for the first time. This has been specifically seen with rabies vaccine, but might happen for any other antigen. Older dogs vaccinated for the first time against rabies (pet travel scheme) showed difficulties reaching titres above 0.5 UI/ml compared to younger dog. Based on that fact, in old dogs and cats in which a non-core or circumstantial vaccines is needed for whatever reason (travelling, moving, changing life style), a single dose might not be enough to ensure a proper immunization and a second dose would be required. However, there is a lack of knowledge on that and if there would be differences between animals and vaccines. So, any decision taken on that issue would be an empirical decision.

3.  All studies on immune function in old cats have been made in healthy geriatric cats, so there is no scientific data about vaccination responses in old dogs and cats suffering from chronic inflammatory diseases or a proinflammatory state. Based on that, dogs and cats with clinically stable chronic conditions should be vaccinated following the usual schedule. However, priority should be given to the diagnosis and treatment to common geriatric diseases instead of "just vaccinating" when attending old dogs and cats in practice. Some experts would recommend serological testing before vaccination in old dogs and cats to avoid unnecessary boosters, if antibody levels are protective. This procedure is difficult to routinely implement in clinical practice, but in some particular cases and owners would be appreciated.

References

1.  Pittari J, Rodan I, Beekman G, Gunn-Moore D, Polzin D, Taboada J, Tuzio H, Zoran D. American Association of Feline Practitioners. Senior care guidelines. J Feline Med Surg. 2009;11(9):763–778.

2.  Senior Care Guidelines Task Force, AAHA, Epstein M, Kuehn NF, Landsberg G, Lascelles BD, Marks SL, Schaedler JM, Tuzio H. AAHA senior care guidelines for dogs and cats. J Am Anim Hosp Assoc. 2005;41(2):81–91.

3.  Day MJ, Horzinek MC, Schultz RD, Squires RA, WSAVA. WSAVA guidelines for the vaccination of dogs and cats. J Small Anim Pract. 2016;57(1):E1–E45.

4.  Day MJ. Ageing, immunosenescence and inflammageing in the dog and cat. J Comp Pathol. 2010;142(Suppl 1):S60–S69.

5.  Schultz RD, Thiel B, Mukhtar E, Sharp P, Larson LJ. Age and long-term protective immunity in dogs and cats. J Comp Path. 2010;142:S102–S108.

6.  Kennedy LJ, Luntb M, Barnes A, McElhinney L, Fooks AR, Baxter DN, Ollier WE. Factors influencing the antibody response of dogs vaccinated against rabies. Vaccine. 2007;25:8500–8507.

7.  Horzinek MC. Vaccination protocols for companion animals: the veterinarian's perspective. J Comp Pathol. 2010;142(Suppl. 1):S129–S132.

8.  Scott FW, Geissinger CM. Duration of immunity in cats vaccinated with an inactivated feline panleukopenia, herpesvirus and calicivirus vaccine. Feline Practice. 1997;25:12–19.

9.  Scott FW, Geissinger CM. Long-term immunity in cats vaccinated with an inactivated trivalent vaccine. Am J Vet Res. 1999;60:652–658.

10. Fortney WD. Implementing a successful senior/geriatric health care program for veterinarians, veterinary technicians, and office managers. Vet Clin North Am Small Anim Pract. 2012;42:823–834.