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Immunocontraception of Deer



Contents of Part 2- Immunocontraception
2.1 How does it work?
2.2 Has it been tried out?
2.3 Is it safe?
2.4 So should we try this vaccine out here?

2 PZP Immunocontraception
Many people have sought to find a non-lethal alternative to culling deer.
Such research as there has been has centred on using various forms of
contraception to reduce the birth rate.
While a fair amount has been published on this, it's difficult for a
non-biochemist to trawl through the scientific literature to find out
exactly what's what.

By far the most promising method for this is 'immunocontraception'. This
means utilising the animals own immune system to prevent pregnancy. Of the
various systems that have been devised, 'PZP' (porcine or pig zona
pellucida) vaccination is the most widely advocated.

2.1 How does it work?
Zona pellucida is a protein that surrounds mammalian egg cells. It forms a
kind of jelly like layer around the egg cell. The principle of this
vaccination is that by administering zona pellucida from pigs, the immune
system will produce antibodies that bind to the egg and prevent the entry of
sperm. The protein is very similar in different species of mammals, so in
principle taking ZP from one species and using it in another can work. That
said there is sufficient variation in this protein between species that we
cannot assume a single vaccine will be applicable in any species until it
has been tested.For example:

Differences between antigenic determinants of pig and cat zona pellucida
Jewgenow K, Rohleder M, Wegner I
119: (1) 15-23 MAY 2000
"Purified zona pellucida proteins obtained from pig and cat ovaries were
used to produce highly specific antisera in rabbits. Antibodies against pZP
raised in rabbits or lions were not effective inhibitors of either in vitro
sperm binding (cat spermatozoa to cat oocytes) or in vitro fertilization in
cats, whereas antibodies against feline zona pellucida proteins (fZP) raised
in rabbits showed a dose-dependent inhibition of in vitro fertilization."

It is therefore premature to assume that the PZP vaccine as is will work on
all species of deer.

Because the protein is so well conserved between species, the body isn't
terribly good at recognising it as 'foreign'. Like in many other
vaccinations, another compound must be added to give the immune system a
helpful boost, to make it respond to the protein. This is called an
adjuvant. Therefore, in any assessment of the safety and effectiveness of a
vaccine, the complete mix that makes up the vaccine must be taken into

2.2 Has it been tried out?
PZP has been piloted in a number of trials, on deer populations this has
been done in the United States.

That PZP immunocontraception has worked well to reduce pregnancy rates in
white-tailed deer. For example;

The effect of immunocontraception on the behavior and reproduction of
white-tailed deer
McShea WJ, Monfort SL, Hakim S, Kirkpatrick J, Liu I, Turner JW, Chassy L,
Munson L
61: (2) 560-569 APR 1997
"Immunocontracepted females exhibited increased activity compared to
non-treated females, presumably reflecting an increased number of estrus
intervals. Similarly, enclosure bucks exhibited an extended breeding season
compared to males in the surrounding wild population. The 2-injection PZP
regimen provided effective contraception during both years of the study."


Effectiveness, reversibility, and serum antibody titers associated with
immunocontraception in captive white-tailed deer
Turner JW, Kirkpatrick JF, Liu IKM
60: (1) 45-51 JAN 1996
"Our data demonstrate in white-tailed does that PZP vaccination: (1) can
produce contraception for at least 1 breeding season, (2) yields greater
efficacy with multiple injections than with 1 injection, (3) is reversible
within 2 years in 75% of does, (4) is associated with elevated anti-PZP
antibody titers, and (5) can produce a sustained antibody response through
at least 1 breeding season. The titer data suggest that PZP vaccine in
white-tailed deer behaves in a manner physiologically similar to PZP vaccine
effects reported in several other species."

A number of trials are described in on-line sources, such as, and

2.3 Is it safe?
When deciding whether to use such a vaccine, we must also take into account
any potential side effects that it may have. This has also been assessed in
a number of studies.

Immunocontraception of captive exotic species .2. Formosan sika deer (Cervus
nippon taiouanus), axis deer (Cervus axis), Himalayan tahr (Hemitragus
jemlahicus), Roosevelt elk (Cervus elaphus roosevelti), Reeves' muntjac
(Muntiacus reevesi), and sambar deer (Cervus unicolor)
Kirkpatrick JF, Calle PP, Kalk P, Liu IKM, Turner JW
27: (4) 482-495 DEC 1996
"Two Formosan sika deer fawns, two axis deer fawns, one Roosevelt elk calf,
and two sambar deer fawns whose mothers became pregnant after inoculation
with PZP were born healthy. Animals pregnant when inoculations began
included one Formosan sika, one axis deer, and three sambar deer. The sika
deer delivered a healthy fawn, the axis deer delivered a stillborn fawn, one
of the three sambar fawns was stillborn, and a second sambar fawn was
abnormal. Six of 13 sambar deer fawns that were conceived after inoculation
and were exposed to the PZP vaccine, adjuvants, and anti-PZP antibodies
during gestation were born with a variety of weaknesses and health problems
or were stillborn."

Potential consequences and problems with wildlife contraceptives
Nettles VF
9: (1) 137-143 1997
"Concern is expressed that the use of immunocontraception could create
genetic changes in the target population that would influence disease

The concern discussed in this paper is complex. By administering a vaccine
that prevents deer with stronger immune systems from breeding, it is feared
that diseased, immunocompromised deer will breed at the expense of healthier
deer, passing on greater susceptibility to disease to the next generation.

Antibody response of elk immunized with porcine zona pellucida
Garrott RA, Cook JG, Bernoco MM, Kirkpatrick JF, Cadwell LL, Cherry S,
Tiller B
34: (3) 539-546 JUL 1998
"High individual variability in immune response observed in this study
suggests it may be difficult to predict the proportion of animals
effectively treated. Disruption of seasonal synchrony in calving also could
occur if antibody levels in individuals fall below effective levels while
animals are still cycling."

Behavioural changes, such as those highlighted in the study by McShea et al.
above must also be taken into account. Another study looking at this was:

Behavioral response of free-ranging elk treated with an immunocontraceptive
Heilmann TJ, Garrott RA, Cadwell LL, Tiller BL
62: (1) 243-250 JAN 1998
"We tested the hypothesis that breeding behavior would be prolonged in
PZP-treated cows due to repeated estrus cycling. Sexual interaction rates of
treatment and control cows were similar during the normal breeding season (P
= 0.96) but differed significantly during the postbreeding season (P <
0.001), when almost no sexual interactions were observed in control cows."
"We recommend population-level experiments to further our understanding of
the effects of contraceptive technologies on the behavior and dynamics of
free-ranging ungulate herds."

It is clear from these studies that while this drug may be effective in
limiting the number of births in a wild population, the side effects are as
yet poorly understood, and before any population-wide application can be
condoned, significant studies must be carried out with the specific deer
species to ascertain the extent of any adverse effects.

The question of what scale of population of deer can be treated with PZP
must also be addressed. Trials to date have concentrated on small scale,
geographically isolated populations with no natural predators.

One of the better-known trials is detailed in this study.

Evaluating immunocontraception for managing suburban white-tailed deer in
Irondequoit, New York
Rudolph BA, Porter WF, Underwood HB
64: (2) 463-473 APR 2000
"Our objectives were to estimate effort required to apply porcine zona
pellucida (PZP) to individual deer and assess the utility of using
immunocontraception to control growth of deer populations. The study was
conducted in a 43-km(2) suburban community with about 400 deer. Effort per
deer was measured as time required to capture and mark deer, and then to
apply booster immunocontraceptive treatments by remote injection."
"Immunocontraception has the best potential for holding suburban deer
populations between 30 and 70% of ecological carrying capacity, but is
likely to be useful only in localized populations when the number of females
to be treated is small (e.g., less than or equal to 200 deer)."

A more general model is discussed in this study:

Effects of fertility control on populations of ungulates: General,
stage-structured models
Hobbs NT, Bowden DC, Baker DL
64: (2) 473-491 APR 2000
"(1) More than 50% of fertile females will need to be maintained infertile
to achieve meaningful reductions in ungulate numbers even when fertility
rates are low (2) The relationship between the proportion of females
maintained infertile and the steady state density is highly nonlinear. This
means that small errors in estimating levels of infertility can lead to
large errors in achieved density. It also means that managers should expect
to see little change in steady-state density across a broad range of
delivery rates. (3) The efficacy of fertility control as a management
technique depends strongly on the persistence of the effect of the fertility
control agent and the ability of managers to recognize previously treated
animals. (4) Fertility control using long-lived agents can be more efficient
than culling in regulating ungulate numbers. (5) Treating small populations
with irreversible agents magnifies the likelihood of population extinction
relative to treatment by culling. As with all techniques, managing
population fertility must extend from a sound understanding of the influence
of management actions on the state and dynamics of the population."

In plain English, this means that to effectively use this technology to
maintain a stable, sutstainable population is fraught with difficulties.
Very small errors in the rate of application of the vaccine could lead to
large differences in population, and even with a very low fertility rate a
large proportion of the females must be treated.

The published research to date does not advocate the widespread application
of PZP, nor does it clearly demonstrate the effectiveness or safety of that
vaccine in any of our native deer. Indeed, the recommendations from these
studies are that this kind of treatment will only be useful for small,
contained populations in which detailed population and physiological studies
have been conducted. None of this applies to species of deer in the UK,
where a lack of natural predation means that the overpopulation problem is
more general, and appropriate physiological, efficacy and population studies
have not been conducted.

2.4 So should we try this vaccine out here?
As mentioned above, the decision as to whether to use a product like this
must be based upon a sound understanding of the mode of action of the whole
vaccine and the implication for conservation management.

When we look in greater depth into the makeup of the PZP vaccine, successful
trials published to date have incorporated 'Freunds complete adjuvant' in
their formulation. This is an oil-in water emulsion, containing in it dead
cells of Mycobacterium tuberculosis. This is an intensely powerful
immuno-stimulant, much used in research but not generally considered
appropriate for use in final applications. For a good discussion of this,

Adjuvants And Their Modes Of Action
Alexander J, Brewer JM
42: (2-3) 153-162 Jun 1995
"Freund's Complete Adjuvant (FCA) has been used experimentally and does
stimulate cellular immunity, but is unsuitable for human and veterinary use
as it promotes, amongst other toxic side effects, local inflammation and
granuloma formation at the site of injection."

The FDA has numerous documents governing the development of new vaccines. It
is quite clear that the use of non-standard adjuvants is not encouraged
(this taken from FDA Docket No. 97N-0029)

"Currently, the only adjuvants included in U.S. licensed vaccines are
aluminum compounds. An adjuvant shall not be introduced into a product
unless there is satisfactory evidence that it does not affect adversely the
safety or potency of the product."
"If a manufacturer contemplates incorporating an adjuvant other than
aluminum compounds into combination vaccine formulations for preventable
infectious diseases, discussions with CBER should be initiated early in
product development regarding appropriate preclinical and clinical studies.
Potential safety concerns for investigational adjuvants include injection
site reactions (e.g., pain, induration, erythema, granuloma formation,
sterile abscess formation), fever, other systemic adverse effects (e.g.,
nausea, malaise, headache), immune mediated events (e.g. anaphylaxis,
uveitis, or arthritis), systemic chemical toxicity to tissues or organs,
teratogenicity, and carcinogenicity."

The regulations governing this are more specifically laid out in CFR 610.15.
"An adjuvant shall not be introduced into a product unless there is
satisfactory evidence that it does not affect adversely the safety or
potency of the product"

Considering the medical and veterinary implications of using FCA, the FDA
would not approve the use of this drug formula.

Another significant factor in the development of a new vaccine is whether
its use would have any wider implication for wildlife management or farming.
Unfortunately, one of the effects of FCA is that as it contains dead
Mycobacterium tuberculosis cells, it stimulates an immune response to them.
This bacterium causes tuberculosis, meaning that treated animals will give a
false-positive test for that condition (somewhat similar to the tuberculin
test given prior to the BCG injection).

The importance of monitoring this condition is shown by this work:

The Epidemiology Of Mycobacterium-Bovis Infections In Animals And Man - A
Oreilly LM, Daborn CJ
76: 1-46, Suppl. 1 AUG 1995
"Tuberculosis is primarily a respiratory disease and transmission of
infection within and between species is mainly by the airborne route,
Mycobacterium bovis, the cause of bovine-type tuberculosis, has an
exceptionally wide host range, Susceptible species include cattle, humans,
non-human primates, goats, cats, dogs, pigs, buffalo, badgers, possums, deer
and bison, Many susceptible species, including man, are spillover hosts in
which infection is not self-maintaining. In countries where there is
transmission of infection from endemically infected wildlife populations to
cattle or other farmed animals, eradication is not feasible and control
measures must be applied indefinitely, Possible methods of limiting spread
of infection from wildlife to cattle including the use of vaccines are
outlined, The usefulness of DNA fingerprinting of M. bovis strains as an
epidemiological tool and of BCG vaccination of humans and cattle as a
control measure are reviewed."

Detection of tuberculosis in deer is already a difficult task;

Etiology, Pathogenesis And Diagnosis Of Mycobacterium-Bovis In Deer
Griffin JFT, Buchan GS
40: (1-2) 193-205 May 1994
"The unique susceptibility of cervidae to mycobacteria in general has meant
that diagnosis of tuberculosis in deer using conventional intradermal
tuberculin tests may be unsatisfactory. Tuberculin testing in deer is more
technically demanding than in cattle, with the cervical region being the
most sensitive area. False positive skin reactions occur widely in
non-diseased deer while seriously infected animals may be ''anergic'' and
fail to react (false negative)."

We can say from these two studies that widespread false positive testing of
deer for BTB in the UK would be catastrophic for the deer population. To
remove our ability to detect this condition in a major wild host for the
disease would mean culling on an unprecedented scale following the first
outbreak of this disease, all wild deer testing positive would be culled.
One only needs to think of the recent slaughter of badgers in the South West
of England to see the severity of this issue.

From these papers showing the risk of false positive tuberculin tests, and
from the information presented above on the side effects of Freunds complete
adjuvant, it is hardly surprising that the Humane Society of the United
States (HSUS), a strong advocator of this vaccine, came to this conclusion

".we must find a vaccine formulation that uses an adjuvant (an immune-system
booster) that is acceptable to the U.S. Food and Drug Administration
(FDA)-the current formulation, which incorporates Freund's Complete Adjuvant
in the initial treatment, will not be approved by the FDA."

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