Research in Veterinary Science 94 (2013) 132–137

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Research in Veterinary Science

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Morbillivirus infection in cetaceans stranded along the Italian coastline:Pathological, immunohistochemical and biomolecular findings

Giovanni Di Guardo a,⇑, Cristina Esmeralda Di Francesco a, Claudia Eleni b, Cristiano Cocumelli b,Francesco Scholl b, Cristina Casalone c, Simone Peletto c, Walter Mignone d, Cristiana Tittarelli d,Fabio Di Nocera e, Leonardo Leonardi f, Antonio Fernández g, Federica Marcer h, Sandro Mazzariol i

a University of Teramo, Faculty of Veterinary Medicine, Teramo, Italyb Istituto Zooprofilattico Sperimentale (IZS) delle Regioni Lazio e Toscana, Rome, Italyc IZS del Piemonte, Liguria e Valle d’Aosta, Turin, Italyd IZS del Piemonte, Liguria e Valle d’Aosta, Imperia, Italye IZS del Mezzogiorno, Salerno, Italyf University of Perugia, Faculty of Veterinary Medicine, Perugia, Italyg University of Las Palmas, Gran Canaria, Canary Islands, Spainh University of Padua, Department of Animal Medicine, Production and Health, Padua, Italyi University of Padua, Department of Comparative Biomedicine and Food Science, Padua, Italy

a r t i c l e i n f o

Article history:Received 8 May 2012Accepted 28 July 2012

Keywords:MorbillivirusInfectionPathogenesisEncephalitisCetaceansStrandingsItalyMediterranean Sea

0034-5288/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.rvsc.2012.07.030

⇑ Corresponding author.E-mail address: gdiguardo@unite.it (G. Di Guardo)

a b s t r a c t

Morbilliviruses are recognized as biological agents highly impacting the health and conservation status offree-ranging cetaceans worldwide, as clearly exemplified by the two Dolphin Morbillivirus (DMV) epidem-ics of 1990–1992 and 2006–2008 among Mediterranean striped dolphins (Stenella coeruleoalba). Afterthese two epidemics, morbilliviral infection (MI) cases with peculiar neurobiological features werereported in striped dolphins stranded along the Spanish coastline. Affected cetaceans showed a suba-cute-to-chronic, non-suppurative encephalitis, with brain lesions strongly resembling those found inhuman ‘‘subacute sclerosing panencephalitis’’ and ‘‘old dog encephalitis’’. Brain was the only tissue in whichmorbilliviral antigen and/or genome could be detected.

Beside a case of morbilliviral encephalitis in a striped dolphin’s calf stranded in 2009, we observed 5additional MI cases in 2 striped dolphins, 1 bottlenose dolphin (Tursiops truncatus) and 2 fin whales (Bal-aenoptera physalus), all stranded in 2011 along the Italian coastline. Noteworthy, 3 of these animals (2striped dolphins and 1 bottlenose dolphin) showed immunohistochemical (IHC) and/or biomolecular(PCR) evidence of morbilliviral antigen and/or genome exclusively in their brain, with 1 striped dolphinand 1 bottlenose dolphin also exhibiting a non-suppurative encephalitis. Furthermore, simultaneous IHCand PCR evidence of a Toxoplasma gondii coinfection was obtained in 1 fin whale.

The above results are consistent with those reported in striped dolphins after the two MI epidemics of1990–92 and 2006–2008, with evidence of morbilliviral antigen and/or genome being found exclusivelyin the brain tissue from affected animals.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Morbilliviruses have been recognized, for at least 25 years, asbiological agents of great concern for free-ranging cetaceans (VanBressem et al., 2009). Before the end of 2006, a morbilliviral epi-demic was reported in pilot whales (Globicephala melas) aroundGibraltar (Fernández et al., 2008) and, in the following months,in striped dolphins (Stenella coeruleoalba) and pilot whales alongthe Spanish Mediterranean coast (Raga et al., 2008). Apart from

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its milder mortality rate, this outbreak shared many similaritieswith the mass die-off of striped dolphins which occurred between1990 and 1992 in the Mediterranean Sea and that was caused by anewly identified agent, Dolphin Morbillivirus (DMV) (Domingoet al., 1990, 1992; Barrett et al., 1995; Kennedy, 1998; Di Guardoet al., 2005; Di Guardo et al., 2011c; Raga et al., 2008; Van Bressemet al., 2009). The virus responsible for the 2006–2008 mortalityepisodes showed a close genetic proximity to the DMV strain caus-ing the dramatic die-off which took place 15 years before in thesame area (Fernández et al., 2008; Raga et al., 2008; Van Bressemet al., 2009; Bellière et al., 2011). Direct evidence of morbilliviralinfection (MI) has been recently reported in several striped

G. Di Guardo et al. / Research in Veterinary Science 94 (2013) 132–137 133

dolphins, a pilot whale and a bottlenose dolphin (Tursiops trunca-tus) stranded on the French Mediterranean coast (Keck et al.,2010), as well as in a striped dolphin (Di Guardo et al., 2011a)and in a fin whale (Balaenoptera physalus) stranded along the Tyr-rhenian coast of Italy, the latter of which showing a Toxoplasmagondii coinfection (Mazzariol et al., 2012).

Similarly to what reported after the DMV epidemic in 1990–1992 (Domingo et al., 1995), a number of peculiar MI cases wereobserved in striped dolphins stranded along the coasts of Spain(Soto et al., 2011) and Italy (Di Guardo et al., 2011a). Affected ceta-ceans showed a subacute-to-chronic, non-suppurative encephali-tis, with brain lesions in Spanish dolphins resembling thosefound in both human ‘‘subacute sclerosing panencephalitis’’ (SSPE)and ‘‘old dog encephalitis’’ (ODE) (Domingo et al., 1995; Sotoet al., 2011). Brain was the only tissue in which morbilliviral anti-gen and/or genome could be detected in all these cases (Domingoet al., 1995; Di Guardo et al., 2011a; Soto et al., 2011).

The present work was aimed at reporting the results of patho-logical, immunohistochemical and biomolecular investigations incetaceans stranded along the Italian coastline after the 2006–2008 epidemic, trying to compare our findings with those reportedin Morbillivirus-infected striped dolphins stranded along the coastof Spain during the same period of time.

2. Materials and methods

We investigated 6 cetaceans stranded along the coast of Italybetween 2009 and 2011, 3 of which being striped dolphins (1 malecalf, 1 adult male and 1 adult female), 1 an adult male bottlenosedolphin and 2 fin whales (1 adult male and 1 subadult female).Apart from the striped dolphin’s calf (stranded in November2009), the remaining 5 animals were found stranded ashore in2011, with 2 of them being live-stranded (the bottlenose dolphinand the female whale). The northern Tyrrhenian (adult male finwhale), the central Tyrrhenian (striped dolphin’s calf, adult femalestriped dolphin and adult male bottlenose dolphin), the southernTyrrhenian Sea (adult male striped dolphin) and the northern coastof Sardinia (subadult female fin whale) were the stranding sites.Details of the 6 cetaceans under study, including their decomposi-tion codes (Geraci and Lounsbury, 2005) and stranding sites, areshown in Table 1.

A detailed post mortem examination was carried out on the 6animals, with representative samples from their organs and tissuesbeing promptly fixed in 10% neutral buffered formalin for histolog-ical investigations. Portions of the same tissues were also frozen at�20 �C for parasitological and microbiological studies, as well asfor ecotoxicological investigations (not dealt with in this article).Furthermore, biomolecular investigations for Morbillivirus and T.gondii were performed, respectively by means of RT-PCR (Frisket al., 1999) and PCR techniques (Di Guardo et al., 2011b; Mazzariolet al., 2012), on selected tissue specimens (brain, lung, spleen, mes-enteric and pulmonary lymph nodes, heart and skeletal muscle).The specificity of biomolecular results was further confirmed bymeans of a nested PCR technique (amplifying an internal fragment

Table 1Details of the 6 stranded cetaceans under study.

ID No. Species Sex Age Decompositio

1 SD M Calf 12 SD F Adult 13 SD M Adult 14 BD M Adult 05 FW M Adult 36 FW F Subadult 0

BD = Bottlenose dolphin; FW = Fin whale; SD = Striped dolphin; F = Female; M = Male.

of the Morbillivirus nucleoprotein gene template previously ob-tained by RT-PCR), along with sequencing and RFLP analysis (Maz-zariol et al., 2012).

Parallel immunohistochemical (IHC) investigations were alsocarried out on the same tissues from the animals under study, uti-lizing a commercially available monoclonal antibody (MoAb)against the nucleoprotein (N) antigen of Canine Distemper Virus(CDV) and a commercially available goat polyclonal Ab against T.gondii, respectively (VMRD Inc, Pullman, WA, USA) (Di Guardoet al., 2010; Mazzariol et al., 2012).

Finally, serological investigations against Morbillivirus, T. gondiiand Brucella spp. were performed, whenever possible, on suitableserum samples obtained by centrifugation (at 1000–1500 rpm for15 min) of blood clots freshly collected from the heart chambersand/or major vessels, as reported elsewhere (Dubey et al., 2005;Di Guardo et al., 2010).

3. Results

The nutritional status and the main anatomo-histopathologicalfindings observed in the 6 cetaceans under study are reported inTable 2. Noteworthy, 3 animals (the striped dolphin’s calf, the bot-tlenose dolphin and the subadult female fin whale) showed a mul-tifocal, non-suppurative meningo-encephalitis (Figs 1 and 2), withmultinucleate syncytia being occasionally found scatteredthroughout the brain lesions in the striped dolphin’s calf (Fig. 3),as well as in prescapular and pulmonary lymph nodes from thesubadult fin whale. Furthermore, a coagulase+ Staphylococcus aur-eus strain was recovered from the brain, lung, liver and kidney ofthe bottlenose dolphin, which also exhibited a suppurative menin-gitis and choroiditis, along with a suppurative-necrotic broncho-pneumonia and a suppurative nephritis (Fig. 4; Table 2).

As far as biomolecular and IHC investigations for Morbillivirusand T. gondii are concerned, their results are shown in Table 3. Inthis respect, beside the peculiar case of morbilliviral encephalitisdescribed in the young striped dolphin stranded in 2009 (Di Guar-do et al., 2011a), we observed 3 additional MI cases in which af-fected cetaceans (2 striped dolphins and the bottlenose dolphin)showed IHC and RT-PCR evidence of morbilliviral antigen and/orgenome exclusively in their brain (Figs 5 and 6). Furthermore,simultaneous IHC and PCR detection of a T. gondii coinfectionwas obtained in the adult fin whale, as reported elsewhere (Mazza-riol et al., 2012).

Morbilliviral and non-morbilliviral encephalitis, along withpneumonia and bacterial sepsis, either due to S. aureus (as in theadult male bottlenose dolphin), or due to Klebsiella spp. (as in thesubadult female fin whale), were the likely causes of death in thecetaceans investigated herein.

Serological investigations against Morbillivirus yielded positiveresults only in the striped dolphin’s calf, with a 1:10 virus neutral-ization (VN) titre being detected in this animal. Furthermore, weobtained no evidence of anti-Brucella spp. Abs in all sera examined,with anti-T. gondii Abs being also found in the adult female striped

n code Stranding site Stranding date

Central Tyrrhenian Sea coast November 15, 2009Central Tyrrhenian Sea coast June 29, 2011Southern Tyrrhenian Sea coast July 02, 2011Central Tyrrhenian Sea coast June 29, 2011Northern Tyrrhenian Sea coast January 25, 2011Northern coast of Sardinia October 03, 2011

Tabl

e2

Nut

riti

onal

stat

usan

dm

ain

anat

omo-

hist

opat

holo

gica

lfi

ndin

gsob

serv

edin

the

6st

rand

edce

tace

ans

unde

rst

udy.

ID No.

Spec

ies

Nu

trit

ion

alst

atu

sM

enin

go-e

nce

phal

itis

(ME)

Pneu

mon

ia/B

ron

cho-

pneu

mon

ia(P

/BP)

Hep

atop

ath

y/H

epat

itis

(H)

Nep

hro

path

y/N

eph

riti

s(N

)En

teri

tis

(E)

Sple

nit

is(S

)Ly

mph

aden

opat

hy/

Lym

phad

enit

is(L

)Pa

rasi

tic

lesi

ons

1SD

Subo

ptim

alN

on-s

upp

ura

tive

mu

ltif

ocal

ME

Lym

phoi

din

ters

titi

alP/

Cat

arrh

alB

PLi

pido

sis

ND

Ch

ron

icca

tarr

hal

E

ND

ND

Inte

stin

alm

icro

gran

ulo

mas

asso

ciat

edw

ith

Tetr

abot

hriu

mfo

rste

ri

2SD

Poor

ND

/Coa

gula

se+

Stap

hylo

cocc

usau

reus

Lym

phoi

din

ters

titi

alP/

Supp

ura

tive

BP

ND

ND

ND

Ch

ron

icpl

asm

ocyt

icS

Lym

phoi

dde

plet

ion

and

kary

orrh

exis

ND

3SD

Subo

ptim

alN

DLy

mph

oid

inte

rsti

tial

PN

DN

DN

DN

DLy

mph

oid

depl

etio

nN

D

4B

DPo

orN

on-s

upp

ura

tive

mu

ltif

ocal

ME/

Supp

ura

tive

mu

ltif

ocal

ME

due

toco

agu

lase

+S.

aure

us

Lym

phoi

din

ters

titi

alP/

Supp

ura

tive

and

nec

roti

cB

Pdu

eto

coag

ula

se+

S.au

reus

Ch

ron

icm

ult

ifoc

alH

due

toco

agu

lase

+S.

aure

us

Supp

ura

tive

mu

ltif

ocal

Ndu

eto

coag

ula

se+

S.au

reus

Ch

ron

icca

tarr

hal

E

ND

Ch

ron

icre

acti

veL

Ch

ron

icgr

anu

lom

atou

spa

nn

icu

liti

spr

esu

mab

lydu

eto

para

siti

cla

rval

mig

rati

on/

Ch

ron

icgr

anu

lom

atou

sga

stri

tis

like

lydu

eto

Phol

eter

gast

roph

ilus

5FW

Poor

ND

ND

Mas

sive

hep

atic

con

gest

ion

Mil

dbi

late

ral

hyd

ron

eph

rosi

sN

DD

iffu

sesp

len

icco

nge

stio

nC

onge

stiv

em

esen

teri

cL

Seve

rein

fest

atio

nby

Penn

ella

spp.

diff

use

lyin

volv

ing

the

skin

/Pro

tozo

ancy

sts

inm

yoca

rdia

lan

dre

nal

tiss

ues

/Bil

ater

alh

ydro

nep

hro

sis

pres

um

ably

due

toCr

assi

caud

asp

p.6

FWPo

orN

on-s

upp

ura

tive

mu

ltif

ocal

ME

Non

-su

ppu

rati

vebr

onch

iolo

-in

ters

titi

alP/

Kle

bsie

llasp

p.is

olat

edfr

omlu

ng

Mil

dn

on-

supp

ura

tive

H/

Kle

bsie

llasp

p.is

olat

edfr

omli

ver

Mil

dch

ron

icin

ters

titi

alN

Mil

dca

tarr

hal

E

Lym

phoi

dde

plet

ion

asso

ciat

edw

ith

mil

dco

nge

stio

n/K

lebs

iella

spp.

isol

ated

from

sple

en

Mar

ked

lym

phoi

dde

plet

ion

,wit

hoc

casi

onal

syn

cyti

ain

pres

capu

lar

and

pulm

onar

yly

mph

nod

es

Para

siti

cla

rvae

and

eggs

ofCr

assi

caud

asp

p.in

ren

alpe

lvis

,as

wel

las

inbl

ood

and

lym

phat

icve

ssel

s

BD

=B

ottl

enos

edo

lph

in;

FW=

Fin

wh

ale;

SD=

Stri

ped

dolp

hin

;N

D=

Not

dete

cted

.

134 G. Di Guardo et al. / Research in Veterinary Science 94 (2013) 132–137

dolphin and in the bottlenose dolphin, in which 1:640 and 1:5120positive titres were observed, respectively.

4. Discussion

On the basis of our results, MI continues to represent a reason ofconcern for Mediterranean cetaceans, with species other than thestriped dolphin – such as bottlenose dolphin and fin whale – beingthreatened by and succumbing to this infection. The pathogenicpotential of morbilliviruses for cetaceans is well documented byseveral works, with striped dolphins and pilot whales being, eitherindividually or jointly, the species most dramatically involved inthe two major epidemics occurred in the Mediterranean during1990–1992 and 2006–2008, respectively (Domingo et al., 1990,1992; Barrett et al., 1995; Kennedy, 1998; Di Guardo et al., 2005;Di Guardo et al., 2011c; Fernández et al., 2008; Raga et al., 2008;Van Bressem et al., 2009).

Noteworthy, 3 Morbillivirus-infected cetaceans investigatedherein showed simultaneous evidence of a T. gondii coinfection,which was ascertained either directly (as in the adult male finwhale) or indirectly (as in the adult female striped dolphin andin the bottlenose dolphin), with high anti-T. gondii Ab titres beingdetected in the latter two animals. Coinfection with T. gondii, anopportunistic pathogen for cetaceans (Van Bressem et al., 2009;Di Guardo et al., 2011c), was reported in several DMV-infectedstriped dolphins during the 1990–92 Mediterranean Sea epidemic(Domingo et al., 1992; Kennedy, 1998). Although the strong immu-nosuppressive potential displayed by morbilliviruses in aquaticmammals may well explain the occurrence of a T. gondii coinfec-tion (Kennedy, 1998; Di Guardo et al., 2005), it should be alsoemphasized that the high tissue concentrations of immunotoxicenvironmental pollutants – such as organochlorinated contami-nants – measured in our DMV- and T. gondii-coinfected fin whalemay have caused an even more dramatic immune response impair-ment in this host (Mazzariol et al., 2012). Nevertheless, there arealso instances in which T. gondii does not apparently behave asan opportunistic but rather as a primary pathogen in free-rangingcetaceans, as recently reported in striped dolphins stranded alongthe Ligurian coast of Italy between 2007 and 2008, in which T. gon-dii occurrence was immunohistochemically and biomolecularlyconfirmed in the brain tissue from 3 animals affected by a multifo-cal, non-suppurative meningo-encephalitis (Di Guardo et al., 2010,2011b). Likewise, the generalized infection by a coagulase+ S. aur-eus strain in the bottlenose dolphin, along with that by Klebsiellaspp. in the subadult fin whale investigated herein, may be convinc-ingly explained as bacterial complications following the primaryMI diagnosed in both cetaceans.

In agreement with previous studies (Baker and Martin, 1992; DiGuardo et al., 1995a,b, 2010), encephalitis – either of morbilliviralaetiology or not – along with pneumonia and bacterial sepsis, werethe likely causes of death for the cetaceans included in this survey.As a matter of fact, encephalitis may represent a highly plausiblecause of death when pathological changes affect vital brain areas,such as the dorsal motor nucleus of the vagus nerve, where the car-dio-respiratory centers are located (Summers et al., 1995; Di Guar-do et al., 2011a).

Notably, no microbiological nor serological evidence of infec-tions caused by Brucella spp., another pathogen of concern for ceta-ceans (Van Bressem et al., 2009; Di Guardo et al., 2011c), wereobtained from any of the stranded animals under investigation.

A particularly challenging and intriguing component of thepresent study refers to the fact that, beside the peculiar case ofmorbilliviral encephalitis reported in the striped dolphin’s calf(Di Guardo et al., 2011a), we observed 3 additional MI cases inwhich affected cetaceans (1 adult female and 1 adult male striped

Fig. 3. Striped dolphin (S. coeruleoalba). Brain. Morbilliviral encephalitis (sameanimal as in Fig. 1). Evidence of multinucleate syncytia scattered throughout theinflamed cerebral parenchyma. Haematoxylin and eosin. Final magnification 500�.

Fig. 2. Fin whale (Balaenoptera physalus). Brain. Morbilliviral encephalitis. Perivas-cular mononuclear cell cuffing is observed in the subcortical grey matter.Haematoxylin and eosin. Final magnification 400�.

Fig. 1. Striped dolphin (Stenella coeruleoalba). Brain. Morbilliviral encephalitis.Mononuclear inflammatory cell cuffing is shown around subcortical blood vessels.Haematoxylin and eosin. Final magnification 250�.

Fig. 4. Bottlenose dolphin (Tursiops truncatus). Lung. Suppurative broncho-pneu-monia. Large Gram+ bacterial aggregates, highly compatible with Staphylococcusaureus colonies, are seen scattered throughout the severe inflammatory lesionsaffecting the pulmonary parenchyma. Gram staining technique. Final magnification62�.

G. Di Guardo et al. / Research in Veterinary Science 94 (2013) 132–137 135

dolphin, along with the adult bottlenose dolphin) showed IHC andRT-PCR evidence of morbilliviral antigen and/or genome only intheir brain, with the striped dolphin’s calf and the bottlenose dol-phin also exhibiting a multifocal, non-suppurative meningo-encephalitis and combined lesions of multifocal, non-suppurativeand suppurative meningo-encephalitis, respectively. A series of pe-culiar MI cases, characterized by IHC evidence of morbilliviral anti-gen exclusively in the brain, had been already described in adultstriped dolphins stranded along the coast of Spain after the1990–92 epidemic. These animals were also affected by a suba-cute-to-chronic encephalitis closely resembling human SSPE- andcanine ODE-associated lesions (Domingo et al., 1995). Noteworthy,a far more consistent number of cases of an SSPE/ODE-like enceph-alitis were subsequently reported in striped dolphins strandedalong the Spanish coastline after the 2006–2008 epidemic, stillwith IHC and biomolecular (RT-PCR) evidence of Morbillivirus anti-gen and genome exclusively restricted to the brain (Soto et al.,2011).

We believe that 4 of the 6 MI cases investigated herein showremarkable similarities with those described in Spanish stripeddolphins (Domingo et al., 1995; Soto et al., 2011). Indeed, all 3striped dolphins and the bottlenose dolphin under study showed

IHC and/or RT-PCR evidence of morbilliviral antigen and/or gen-ome only in their cerebral tissue. Nevertheless, the striped dol-phin’s calf had a multifocal, non-suppurative meningo-encephalitis that was not entirely consistent with SSPE- andODE-related lesions (Di Guardo et al., 2011a), while the bottlenosedolphin exhibited a multifocal, non-suppurative meningo-enceph-alitis, associated with a suppurative meningo-encephalitis mostlikely resulting from brain colonization by a coagulase+ S. aureusstrain. To the best of our knowledge and differently from what re-ported in striped dolphins (Domingo et al., 1995; Soto et al., 2011),no other MI cases showing similar neurobiological features havebeen previously reported in bottlenose dolphins.

A number of pathogenetic mechanisms have been suggested tojustify the prolonged viral persistence within the host’s centralnervous system (CNS), thereby triggering the development of thetypical Measles Virus (MV)- and CDV-induced SSPE- and ODE-re-lated lesions in man and dog, respectively (Rima et al., 1987; Sum-mers et al., 1995; Cosby et al., 2002; Rima and Duprex, 2006).Among such mechanisms, the production of ‘‘escape mutants’’ sec-ondary to the accumulation of point- and hypermutations withinvirus envelope genes (Reuter and Schneider-Schaulies, 2010) is

Table 3Biomolecular (RT-PCR, PCR), IHC, microbiological and serological findings for Morbillivirus, Toxoplasma gondii and Brucella spp. in the 6 stranded cetaceans under study.

IDNumber

Species Morbillivirus T. gondii Brucella spp.

RT-PCR NestedPCR

RFLP Sequencing IHC Serology(VN)

PCR Sequencing IHC Serology(MAT)

Culture Serology(RSA)

1 SD Pos (Brain) ND ND ND Pos(Brain)

1:10 ND ND ND Neg Neg Neg

2 SD Pos (Brain) Pos ND ND Neg Neg ND ND ND 1:640 Neg Neg3 SD Pos (Brain) Pos ND DMV Pos

(Brain)ND ND ND ND ND Neg ND

4 BD Pos (Brain) Pos ND ND Neg Neg Neg ND Neg 1:5120 Neg Neg5 FW Pos (Spleen,

Liver, Lung)ND Pos DMV Neg ND Pos (Kidney,

Heart, Skeletalmuscle,Mesenteric lymphnodes)

T. gondii Pos ND Neg ND

6 FW Pos (Liver,Spleen, Lymphnodes,Skeletalmuscle)

ND ND ND Neg ND Neg ND Neg ND Neg ND

BD = Bottlenose dolphin; FW = Fin whale; SD = Striped dolphin; ND = Not done; Neg = Negative; Pos = Positive; MAT = Microagglutination test; RSA = Rapid serum aggluti-nation; VN = Virus neutralization.

Fig. 5. Striped dolphin (S. coeruleoalba). Brain. Morbilliviral encephalitis. Positiveimmunostaining for Morbillivirus antigen is shown within subcortical neurons aswell as in the surrounding neuropil. Immunohistochemistry (IHC) for Morbilliviruswith a monoclonal antibody (MoAb) against Canine Distemper Virus (CDV) nucle-oprotein (N) antigen. Mayer’s haematoxylin counterstain. Final magnification 250�.

Fig. 6. Results of biomolecular (RT-PCR) investigations for Morbillivirus with a set ofuniversal N gene primers (Frisk et al., 1999). Lane 1: BenchTop 1 Kb DNA Ladder(Promega, Italy); Lanes 3, 4, 6: Positive brain tissue samples from two stripeddolphins (lanes 3 and 4) and one bottlenose dolphin (lane 6). Lanes 2, 5, 7: Negativelung tissue samples from two striped dolphins (lanes 2 and 5; same animals as inlanes 3 and 4) and one bottlenose dolphin (lane 7; same animal as in lane 6). Lane 8:Positive control (Onderstepoort CDV strain); arrow. Lane 9: Negative control(uninfected striped dolphin’s brain).

136 G. Di Guardo et al. / Research in Veterinary Science 94 (2013) 132–137

regarded as an elegant ‘‘adaptive strategy’’ providing the agentwith an extra-capability of ‘‘hiding’’ from host’s immune response,whose efficiency is already physiologically reduced in the CNScompartment (Griffin, 2010). This sounds as a plausible reason be-hind the fact that no anti-Morbillivirus Abs, or a low anti-Morbillivi-rus neutralizing Ab titre (1:10), were respectively detected in thebottlenose dolphin and in the adult female striped dolphin (bothof which DMV-infected), as well as in the striped dolphin’s calfshowing IHC and/or biomolecular (RT-PCR) evidence of morbillivi-ral antigen and/or genome exclusively in their brain. Interestingly,virus persistence within the host’s CNS has been recently linked toa selective mutation process involving the fusion (F) and the ma-trix (M) protein genes of ‘‘brain-restricted/confined’’ isolates recov-ered from Phocine/Phocid Distemper Virus (PDV)-infected commonseals (Phoca vitulina) (Philip Earle et al., 2011). Although these find-ings may underlie a neurobiologic behavior of MI in seals sharingsimilar pathogenetic features with that observed in Spanish and

in our Morbillivirus-infected dolphins, the only ‘‘accredited’’ MImodels to be strikingly mirrored by these cases are represented,

G. Di Guardo et al. / Research in Veterinary Science 94 (2013) 132–137 137

to the best of our knowledge, by human SSPE (Cosby et al., 2002;Rima and Duprex, 2006) and canine ODE (Rima et al., 1987; Sum-mers et al., 1995). Nevertheless, paying also attention to the factthat the highly endangered population of Mediterranean monkseals (Monachus monachus) has been shown to be susceptible tothe devastating effects of a morbilliviral strain closely related toDMV (Monk Seal Morbillivirus-West Africa, MSMV-WA), as well asto the lethal effects of a Porpoise Morbillivirus (PMV)-like isolate(Monk Seal Morbillivirus-Greece, MSMV-G) (Osterhaus et al.,1997; Van de Bildt et al., 1999), there is an urgent need of investi-gating in much more depth the host–virus interaction dynamicsboth in monk seals and in other susceptible pinniped and cetaceanspecies. This would allow, in fact, to properly assess whether MIneurobiology and neuropathogenesis share common traits withthe cases reported in Spanish dolphins as well as with those re-ported herein.

In conclusion, although much work is needed to define thevirus- and the host-related biologic determinants underlying Mor-billivirus infection and persistence within the CNS of cetaceans, wecannot yet rule out the hypothesis that a novel, selectively neuro-tropic morbilliviral strain infected the animals included in thepresent investigation.

Conflict of interest statement

All the authors of this paper disclose any financial and personalrelationships with other people or organizations that could inap-propriately influence (bias) their work.

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