Received: 22 April 2021
Accepted for publication: 27 July 2021
Slov Vet Res 2021: 58 (4): 155 – 8
DOI 10.26873/SVR-1331-2021
UDC 636.7.09:616.211:616.99:595.772(497.4)
Case Report
Introduction
The sheep ectoparasite, Oestrus ovis L. 
(Linnaeus 1758) is commonly known as nasal bot 
fly of sheep, goats, and other wild ruminants (1), 
although infestations of dogs (2, 3, 4, 5, 6), humans 
(7) and a cat (8) have also been documented. It 
has a worldwide distribution, with a preference 
to warmer climate, where adult flies can be active 
year-round (9). In Europe, it has a high prevalence 
in Mediterranean regions, where seroprevalence 
in sheep can reach from 43.3-91% (10, 11, 12). In 
Slovenia, the prevalence was assessed at 40% (13). 
FIRST REPORT OF CANINE MYIASIS WITH SHEEP NASAL BOT FLY, 
Oestrus ovis, IN SLOVENIA
Aleksandra Vergles Rataj*, Petra Bandelj, Vladimira Erjavec, Darja Pavlin
1Veterinary Faculty, University of Ljubljana, cesta V Mestni log 47, SI-1115 Ljubljana, Slovenia
*Corresponding author, Email: aleksandra.verglesrataj@vf.uni-lj.si
Abstract: First larval stage (L1) of Oestrus ovis was recovered by flushing of the nasal cavity during rhinoscopy in an urban 
living dog. The dog was taken to the Small animal clinic after an acute onset of sneezing and bilateral nasal discharge. In Eu-
rope, there are sporadic reports of nasal myiasis in dogs caused by sheep bot flies, and the overall prevalence of O. ovis is high 
in Mediterranean countries. Because of its habitat expansion due to climate change, it should be considered as a differential 
diagnosis when an animal patient presents with signs of rhinitis in areas bordering the Mediterranean climate. This is the first 
report of a dog infested by sheep nasal bot fly in Slovenia.
Key words: Oestrus ovis; sheep bot fly; nasal myiasis; dog; climate change
The presence of the parasite in the population can 
be detrimental to the infested animals (12, 14), as 
the larval stages of the O. ovis invade sinu-nasal 
passages (1). If the infestation is severe, the animal 
may suffer further complication of the respiratory 
system, such as chronic pneumonia unresponsive 
to antimicrobial treatment (15). Reports of dogs 
with O. ovis infestation are rare but show that dogs 
can harbor all stages of larvae, including mature 
larval instar (5). Clinical signs in dogs are mild in 
the early stage of infestation (4) but can become 
severe if symptoms go unnoticed, even leading to 
euthanasia of the animal (3). With some exceptions 
(3), most cases are associated with the dog or cat 
living on a sheep farm or in an area of high sheep 
density (4, 5, 8). 
A. Vergles Rataj, P. Bandelj, V. Erjavec, D. Pavlin156
The aim of this report is to describe the first 
case of sheep nasal bot fly infestation in a dog in 
Slovenia with no history of being in contact with 
sheep or sheep associated areas.
Case presentation
In August 2018, a spayed 4-year-old West 
Highland White Terrier female dog living in the 
city of Ljubljana (latitude 46°03’03’’ N, longitude 
14°30’18’’ E) was presented to the Small animal 
clinic (Veterinary Faculty, University of Ljubljana) 
with frequent sneezing and nose licking of an 
acute onset. The owner reported that the clinical 
signs started after the dog was taken for a walk to 
a nearby meadow field in the city center. Clinical 
examination of the dog revealed low grade serous 
bilateral nasal discharge with no other changes 
in her clinical status. A complete blood count 
was performed to rule out infectious diseases, 
which showed no abnormalities. Based on the 
suspected diagnosis of a nasal foreign body, a 
rhinoscopy was performed the same day. Mild 
oedema and erythema of the mucosal surface 
with several small moving larvae-like structures 
was noticed in the nasal cavity (Figure 1). More 
than 30 larvae-like structures were noted further 
down the nasopharynx. Retrograde irrigation 
of the nasal cavity with saline removed the 
larvae-like structures, which were sent to the 
Parasitology department of the Veterinary Faculty 
(University of Ljubljana) for identification. While 
waiting for a parasitological diagnosis, the dog 
was treated with ivermectin (Ivomec 1%, Merial) 
at a dose of 0.03 mg/kg, applied subcutaneously 
three times at weekly intervals. The owner stated 
that the clinical signs subsided within the first 
week of starting treatment and disappeared 
completely two weeks after the initial diagnosis. 
The sneezing resolved one day after rhinoscopy 
and nasal lavage.
The parasitological diagnosis of first larval 
stage (L1) of Oestrus ovis L (Diptera, Oestridae) 
was made, based on key morphological features 
(16) observed under light microscopy. The 
dorsoventrally flattened L1 was approximately 
1.2 mm long and 0.4 mm wide. The larval body 
was divided into 11 segments, with a pair of 
prominent, dark brown oral hooks on the first 
segment (Figure 2) and caudal spines on the last 
segment (Figure 3).
Figure 1: Multiple Oestrus ovis L1 in the nasopharynx of 
the dog during retroflex nasopharyngoscopy
Figure 2: Oestrus ovis L1 segmented body with two dark 
brown oral hooks (arrow) on the first body segment
Figure 3: Oestrus ovis L1 caudal spines on the last body 
segment
First report of canine myiasis with sheep nasal bot fly, Oestrus ovis, in Slovenia 157
Discussion
Nasal bot fly, Oestrus ovis, causes myasis 
in small ruminants (1), but other casual hosts, 
such as humans (7) and carnivores (2-6, 8) 
have also been reported. The presence of sheep 
nasal bot flies in Slovenia was recorded in 1997 
with a seroprevalence of 40% (13). Since then, 
several cases have been reported in Slovenia, in 
which third stage larvae were identified in sheep 
(unpublished data). In this study, we report the 
first case of O. ovis L1 infestation in a dog in 
Slovenia.
The dog presented in this case, lives in the city 
of Ljubljana, which has a pre-alpine climate. As 
discussed by Zanzani et al (6), climate change 
may have been an important component in the 
spread of O. ovis habitat above 45° N latitude. 
Although there have been sporadic local reports 
of nasal bot fly infestation in sheep, no study has 
been done to determine its prevalence since 1997 
(13). The 4-year-old dog lived most of its life in an 
urban environment. According to the owner, the 
dog had no contact with sheep or areas associated 
with sheep. However, Ljubljana as a city is still 
highly accessible to the rural surroundings, where 
flocks of sheep are present. It is common for dog 
owners who live in the city to walk their dogs 
through the livestock pastures and rural areas, 
especially in the summer. Adult nasal bot flies 
are very active during the hot summer months 
(14, 17) and explains the infestation of the dog in 
August. If the infestation would go unnoticed by 
the owner, the O. ovis L1 would remain quiescent 
during the cold winter months and continued its 
development the following spring (14, 17). This 
was the case of a dog in the UK, where the dog 
expelled the mature larva in the spring of 2011, 
following the presumptive infestation in autumn 
2010 (5).
Reportedly the infestation of O. ovis in dogs 
and cats are less likely than in humans (6), 
where it usually causes ophthalmomyiasis (7, 
18). To the authors knowledge, no human cases 
have been documented in Slovenia to date. 
However, there have been several cases of human 
ophthalmomyiasis in Italy and two recent cases 
in Croatia (7). It is suspected that the incidence 
of ocular myiasis in humans is underreported 
(7), as is with canine cases of nasal myiasis (6). 
Nasal myiasis due to O. ovis infestation should 
be considered as a differential diagnosis when an 
animal is presented with signs of rhinitis, sneezing 
and nasal discharge (3, 4, 6). With climate change 
the prevalence and distribution of O. ovis may 
increase and expand (5) to non-Mediterranean 
regions. In conclusion, it is important to emphasize 
the role of reporting disease occurrence in both, 
animals and humans, and determining the 
prevalence of sheep nasal bot flies in populations 
previously believed not to be at risk.
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PRVI PRIMER PASJE MIAZE Z OVČJIM NOSNIM ZOLJEM, Oestrus ovis, V SLOVENIJI
A. Vergles Rataj, P. Bandelj, V. Erjavec, D. Pavlin
Izvleček: Med rinoskopijo in spiranjem nosne votline, smo pri psu, ki živi v urbanem okolju, ugotovili ličinke prve stopnje 
(L1) zajedavca Oestru ovis. Lastniki so psa pripeljali na Kliniko za male živali po akutnem izbruhu kihanja in bilateralnega 
nosnega izcedka. V Evropi so dokumentirani sporadični primeri nosne miaze pri psih zaradi ovčjega nosnega zolja, O. ovis, 
in skupna prevalenca ovčjega zajedavca je v mediteranskih državah visoka. Zaradi klimatskih sprememb, se habitat nosnih 
zoljev čedalje bolj širi, za kar je pomembno O. ovis vključiti v seznam diferencialnih diagnoz pri pacientih s kliničnimi znaki 
rinitisa tudi na področjih, ki mejijo na mediteransko klimo. To je prvi opisan primer infestacije psa z ovčjim nosnim zoljem v 
Sloveniji.
Ključne besede: Oestrus ovis; ovčji nosni zolj; nosna miaza; pes; podnebne spremembe