Introduction
In a pilot study of horse allergic riders, we were able to show that contact with
ABCR Curly Horses is possible without significant allergic reactions [1]. We observed that the initially mild allergic reactions to Curly Horses in horse
allergic riders decreased the longer they have been in contact with these horses [2]. This is in contrast to the recommendation to avoid contact to the allergen in case
of an allergy to furry animals [3]
[4]. We aimed to investigate in a case study whether clinical tolerance induction to
normal horse breeds is possible by using Curly Horses in a therapeutic approach.
This single case study was conducted in accordance with Good Clinical Practice guidelines
and the provisions of the Declaration of Helsinki. The individual protocol was approved
by an independent ethics committee (Ärztekammer Schleswig Holstein) [5]. Written informed consent was obtained from the patient before trials began.
Case
The 50-year-old polysensitized female patient ([Table 1]) volunteered to test whether contact with Curly Horses would enable her to ride
normal horse breeds again without symptoms. She had given up riding 25 years ago because
of a horse allergy, verified by clinical history, skin prick test and positive nasal
provocation test.
Table 1
Clinical data, lung function results.
|
age/gender
|
50 y/female
|
|
duration of illness
|
rhinoconjunctivitis 44 y bronchial asthma 35 y, eczema 50 y
|
|
allergic symptoms during horse contact
|
rhinoconjunctivitis, bronchial asthma, eczema
|
|
further sensitizations
|
rye, grass, birch, beech pollen, alternaria, cladosporium, cat and dog
|
|
current therapy
|
nasal topic mometasone 100 µg/die[1], budesonide 400 µg/die, montelukast 10 mg/die[1], cetirizine as needed[1], basic therapy (hydrating topical treatment)
|
|
lung function (% predicted)
|
19/03/2016: FEV1 110 % , PEF 116 %
17/09/2016: FEV1 88 %, PEF107 %
|
1 = not 7 days before nasal provocation testing.
Spirometry and rhinomanometry before starting the exposure and at 6 months follow-up
were normal ([Table 1]). The skin prick test showed a reaction of mean 4.0 mm to Curly Horses compared
to 14 mm to other breeds: Histamine: 4 mm; sodium chloride 0,9 %: 0 mm; normal horse
(Bencard®): 16 mm (ps); German riding pony: 14 mm (ps); ABCR Curly horse mares ABCR P 2563:
1 mm, ABCR 3975: 6 mm, ABCR 4059: 10 mm, ABCR stallion ABCR 4056: 4 mm.
During the study period the patient had contact with one of the four Curly mares/gelding
(ABC P 2563, 3975, 4059, ABC4056) outside the stable by riding (60 minutes) and, after
10 times of riding, by brushing (15 minutes) the horses 60 times. Serial PNIF (Clemens
Clarke®) and peak flow/FEV1 measurements (Microloop Care fusion®) before and during horse contact (riding and brushing) were documented every 30 minutes,
and 15 minutes after the contacts. A documentation of concomitant symptoms (conjunctivitis,
rhinitis, dyspnoea, urticaria) was carried out at any point of horse contact.
The initially positive nasal provocation test against normal horse (Allergopharma®) was negative after completion of 60 riding hours on Curly Horses ([Table 2]). We found an increase of IgG horse (Thermofisher®) from 7 mg/l after 6 month to 14 mg/l and 9 months to 29 mg/l.
Table 2
Rhinomanometric and IgG measurement before and after 60 riding hours; nasal provocation
test left nose.
|
date
|
rhinomanometric measurement
|
start
|
% pred.
|
nasal provocation horse
|
Δ %
|
IgG horse mg/l
|
IgE horse
kU/l
|
|
19/03/2016
|
Flow in at V’150 (ml/s)
|
529
|
139
|
297
|
− 56
|
7
|
18
|
|
19/03/2016
|
RAAR in 150 (kpa/s/l)
|
0,28
|
48
|
0,50
|
+ 77
|
|
|
|
17/09/2016
|
Flow in at V’150 (ml/s)
|
539
|
142
|
524
|
− 3
|
14
|
33
|
|
17/09/2016
|
RAAR in 150 (kpa/s/l)
|
0,28
|
47,9
|
0,29
|
+ 1
|
|
|
|
29/12/2016
|
|
|
|
|
|
29
|
37
|
Legend: RAAR = inspiratory resistance at V‘150 ml/s
During the first week of Curly Horse contact (riding), there was a slight, non-significant
decrease of PNIF of maximum − 20 % and FEV1 of maximum − 10 % lung function ([Fig. 1]) during and after riding. After 10 hours of riding, the Curly Horses were brushed
without significantly affecting the patient’s lung or nose function. During further
riding and brushing contact, a continuous lowering of reaction can be derived from
regression analysis in [Fig. 1].
Fig. 1 FEV1 and PNIF reaction during and after riding. Delta FEV1 and Delta PNIF is calculated
as percentage change in relation to the base value taken before each riding hour.
Exposure to a normal horse breed (North English fell pony and German riding pony)
was symptom-free during both brushing and riding after 60 hours of riding on Curly
Horses without changes in the patient’s lung function or rhinomanometry ([Fig. 1], [Fig. 2]).
Fig. 2 Riding on Curly Horse (a) and documentation of contact (brushing/riding) to a German riding pony (b) after 60 riding hours on Curly Horse.
Discussion
It is usually expected that continuous, natural exposure to an allergen increases
the intensity of allergic symptoms over time, as is the case for “Bakerʼs asthma”
or fur animal allergy, and therefore avoidance of exposure is the common recommendation
[3]
[4]
[6]. In contrast, in this case of a horse allergic rider using (ABCR) Curly Horse for
riding may lead to induction of clinical tolerance.
Since 1971 it has been assumed that horse allergic riders show much less allergic
reactions upon contact to Curly Horses than to horses of other breeds [7]. A positive single test for hypoallergenicity for Curly Horses [8] as well as an exclusion of hypoallergenicity by testing the allergen content of
Curly horses [9] in another study have been presented. No further scientific work was available until
2013. In a pilot study of 10 horse allergic riders, a markedly reduced allergic reaction
was observed upon contact with these horses [1], which was then confirmed in an increased number of affected riders [2].
In a self-generated survey on “Facebook groups: Curly Horses International + American
Curly in Europe”, 16 horse allergic Curly-holders/-rider informed us that their allergy
to horses of other breeds decreased significantly or even disappeared after a longer
contact period to Curly Horses.
We have observed that initial allergic reactions in horse-allergic riders were significantly
reduced during the duration of the former study [2]. Thus, many of the riders tested here can easily brush and interact with Curly Horses,
which includes having contact with saliva, without any allergic reactions to these
horses after a period of > 10 riding and contact hours.
The first known desensitization study against horse allergy is a case report from
1921 [10], in which immunotherapy in a 34-year-old patient was achieved placing horse material
on scarified skin. Further reports on immunotherapy in horse allergy are found in
small numbers [11]
[12]
[13]
[14]
[15]. Our case shows the conversion of the nasal provocation test and an increase of
IgG to horse allergens as signs of tolerance induction. This tolerance induction against
normal horses could be achieved in six months after a horse allergic rider has been
in contact with Curly Horses 60 times, which has been verified during an exposure
test to normal horse breeds.
This observation supports the hypothesis that contact to Curly Horses is not only
suitable for horse allergic patients, but can also lead to a clinical tolerance induction
to normal horses, taking into account that this is an uncontrolled case report. This
observation will be systematically examined in a controlled study, ongoing since 2014
[5]. The cause of the hypoallergenicity of Curly Horses used has not yet been clarified.
However, hypoallergenicity can be inferred from the fact that a horse allergic patient
can become immune tolerant to normal horse breeds through contact with Curly Horses.
In contrast to the “Bakerʼs asthma” [6], an avoidance of exposure in horse allergic patients using the examined ABCR Curly
horses seems to be unnecessary, at least in this case.
Abbreviations
ABCR:
American Baskhir Curly Horse Registry
FEV1:
forced exspiratory volume in the 1 second
PNIF:
peak nasal inspiratory flow
Pred:
predicted
Y:
year
Ps:
Pseudopodia
