(Re-) emerging neurotropic viruses

of clinical significance

Prof. Anna Papa, MD, PhD

Aristotle University of Thessaloniki, Greece ESCMID eLibrary

©

by author

A virus that:

1. is newly discovered

2. infected new hosts

3. altered its pathogenic characteristics

4. spread into new geographic areas or reappeared in an

area

5. increased recently its incidence or there is a threat to

increase in the near future

6. All the above

What is the meaning of “emerging” virus?

5831

ESCMID eLibrary

©

by author

(Re-) Emerging viral diseases are diseases caused by viruses that

have:

• been newly discovered (previously unrecognized)

• infected new hosts

• altered characteristics of their pathogenesis

• spread into new geographic areas (like Zika virus in the Americas).

• reappeared in an area

• increased their incidence recently or are threatening to increase in

the near future.

(Re-) Emerging viral diseases

ESCMID eLibrary

©

by author

Factors contributing to emergence of viral diseases• Virus genetic variations

• Environmental factors

changing weather patterns (e.g., El Niño)

damming of rivers, tropical deforestation (alter the abundance and

distribution of virus vectors or hosts, exposure to new vectors)

• Demographic factors

Increase in the human population

urbanization in developing countries

intensification of agriculture

speed and volume of global transportation

Also: Increased capability to identify novel pathogens (improved diagnostic

techniques and enhanced surveillance systems) ESCMID eLibrary

©

by author

Which viruses are mainly affected by environmental

factors?

1. Arboviruses

2. Enteroviruses

3. Respiratory viruses

4. Zoonotic viruses

5830

ESCMID eLibrary

©

by author

Neurotropic viruses

A neurotropic virus is a virus that is capable to infect nerve cells

causing neurological manifestations.

A neurotropic virus is neuroinvasive = capable of entering the nervous

system (overcoming both the extraneural and neural barriers),

and neurovirulent = capable of causing disease within the nervous

system.

Factors contributing to disease’s course and outcome

Host genetics

Host immune system

Virus tropism

Virus capability of spread within the CNS

ESCMID eLibrary

©

by author

FSM

Anatomy of the Blood-Brain-Barrier (BBB)

ESCMID eLibrary

©

by author

Routes of virus spread into the CNS

1. Axonal retrograde transport along motor and olfactory

neurons

2. Haematogenous spread across the BBB

3. Loss of integrity of BBB (changes in endothelial cell

permeability, which is regulated by vasoactive cytokines)

4. Direct infection of brain microvascular endothelial cells

5. Transport of infected macrophages or neutrophils across the

BBB into the brain parenchyma (“Trojan horse” model)

Cho and Diamond 2012

ESCMID eLibrary

©

by author

Early immune response is critical to limiting the neuropathogenesis of

neurotropic viruses.

Innate and adaptive immune responses

are delicately balanced and may help or harm the host

Early control: Innate immune response, including cell-intrinsic

antiviral defenses, the type I IFN response and innate cell-mediated

responses (involving neutrophils, NK cells and γδ T cells)

Late stage control: adaptive immune response, including humoral

and cellural immune responses

Immune response to neurotropic viruses

The level of viremia is correlated with the viral dissemination to the CNS

ESCMID eLibrary

©

by author

Viral Family Virus

Flaviviridae West Nile

Japanese encephalitis

Murray Valley encephalitis

Zika

Usutu

Togaviridae Chikungunya

Phenuiviridae Phleboviruses (Toscana)

Paramyxoviridae Hendra, Nipah

Picornaviridae Enteroviruses 71, D68

Parechovirus type 3

Bornaviridae Borna Disease Virus 1

Astroviridae Astrovirus VA1/HMO-C

Rhabdoviridae Australian bat lyssavirus

(Re)-emerging neurotropic viruses of clinical importance

ESCMID eLibrary

©

by author

Single-strand positive-sensed RNA viruses

Flavivirus genus includes several viruses that are etiological agents of CNS

infections.

Glycosylation of the envelope protein is one determinant of neuroinvasion,

increasing both axonal and trans-epithelial transportation.

Innate immune response is important for controlling brain infection(infection of the brain microvascular endothelium occurs after loss of effective clearance in peripheral sites)

Flaviviridae

ESCMID eLibrary

©

by author

Tick-borne encephalitis (TBE) virus

Transmission: tick bite Ixodes ricinus and I. persulcatus ticks (in Europe),

consumption of unpasteurized dairy products from infected livestock,

needle stick

Reservoir hosts: rodents, insectivores

Incubation period: 7 -14 d after a tick bite, 3–5 d after consumption of

infected milk

Subtypes: European, Siberian, Far-Eastern

Symptoms: Diphasic illness, febrile - neurological; it can result in long-

term neurological symptoms, and even death

Fatality: European 0.5-2%, Siberian 1-3%, Far Eastern up to 35%

TBE is the most important arboviral disease in Europe and central and

eastern Asia, causing approx. 13,000 hospitalizations each year.

TBE is an emerging disease due to its rising incidence and the expansion

in new areas.

I. ricinus

I. persulcatus

ESCMID eLibrary

©

by author

Steps during TBEV infection

Virus transmission

from an infected tick

Replication in

regional lymph nodePrimary viremia

Secondary viremia

Crossing of the BBB

Infection of the brain

In an in vitro BBB model, TBEV crossed the BBB via a transcellularpathway without compromising the integrity of the cell monolayer (Palus et al., 2017).

ESCMID eLibrary

©

by author

2009: first cases in Bulgaria

2014: first case in Greece

2016, first case in the Netherlands

Haditsch & Kunze, 2013

Known, unknown and emerging TBE foci

ESCMID eLibrary

©

by author

Vector: Ixodes spp.

Rare but severe neuroinvasive disease with 50% of survivors displaying

long-term neurological sequelae

Fatality: 10%

The only North American member of the tick-borne encephalitis serogroup

of flaviviruses.

VBZ 2010

ESCMID eLibrary

©

by author

Originally isolated in in the West Nile province of Uganda in 1937

Vectors: Culex mosquitos (mainly C. pipiens)

Host reservoir: resident birds

7 genetic lineages; lineages 1 and 2 are responsible for the major

epidemics in humans.

Incubation period: 3–14 d.

Viremia occurs within 1–3 d and can last up to 11 d.

Groups at risk: elderly, immunocompromised, patients with diabetes,

hypertension, and chronic kidney disease.

Symptoms: most asymptomatic - approx. 20% flu-like illness,

maculopapular rash - <1% neuroinvasive disease: encephalitis (mental

status change, Parkinsonian movement disorders), meningitis or acute

flaccid paralysis, Guillain–Barré-like syndrome (probably as result of

damage to the anterior horn cells). Neurological disability in over half of

patients at 1-year follow-up.

West Nile virus

WNV is an important emerging neurotropic virus,

responsible for encephalitis outbreaks worldwide

ESCMID eLibrary

©

by author

Schematic of WNV pathogenesis in humans

Suthar et al. Nat Rev 2013

WNV replicates in keratinocytes, skin-resident dermal dendritic cells (DCs) and Langerhans cells

Infected DCs migrate to the regional lymph node leading to viraemia

Subsequent infection of peripheral organs (e.g. spleen, kidney and liver). By day 4, viral replication peaks in the spleen and serum.

Between days 6 and 8, WNV is detected within the brain and spinal cord (via multiple routes of entrance)

WNV infects and injures neurons within the brain stem, hippocampus, cortex, cerebellum and spinal cord

ESCMID eLibrary

©

by author

In the European Union, 204 human WNF cases have been reported:Romania (66 cases), Italy (57), Greece (48), Hungary (21), Austria (5),Croatia (5), France (1) and Bulgaria (1). In the neighbouring countries,84 cases were reported: Serbia (49), Israel (28) and Turkey (7).

Many countries reported cases in newly affected areas (areas whereno cases were ever reported before)

Epidemiological update: West Nile virus transmission season in Europe, 2017

ESCMID eLibrary

©

by author

21,574 neuroinvasive disease cases

The largest epidemics of arboviral meningoencephalitis in US history,

the largest epidemics of WNV neuroinvasive disease reported to date

West Nile virus in USA, 1999-2016

Average annual incidence of WNV neuroinvasivedisease reported to CDC by state, 1999-2016

WNV neuroinvasive disease incidence reported to CDC by year, 1999-2016

ESCMID eLibrary

©

by author

Vector: Culex spp. mosquitoes (C. pipiens)

Resevoir hosts: wild birds

2009: USUV detected in human encephalitis cases

African mosquito-borne virus closely related to WNV.

Threat of USUV emergence?

While human cases are infrequent, the potential for neuroinvasive infection

suggests a need for clinical awareness and diagnostic capability

Usutu virus

Italy, retrospective study published in 2017: USUV was the cause of previously unexplained encephalitis suggesting that neurological cases associated to USUV may be more common than previously thought.

Deleterious effect of Usutu virus on human neural cells (Salinas et al. PNTD 2017). USUV efficiently infects neurons, astrocytes, microglia and human neuronal stem cells. When compared to ZIKV, USUV led to a higher infection rate, viral production, and stronger cell death and antiviral response.

Mass mortality in blackbirds (Austria 2001)

ESCMID eLibrary

©

by author

First identified in Japan in the 19th century. Currently in China,

Southeast Asia, India, New Guinea, and Australia. Continues to expand

its geographic range.

Vector: Culex mosquitoes (mainly C. tritaeniorhynchus)

Host reservoirs: pigs, egrets, and herons.

Groups at risk: children

Fatality: 20–25% with 50% rate of severe disability amongst survivors.

The emergence of JEV can be attributed to increased population growth

in endemic areas

Japanese encephalitis virus

The most important cause of viral encephalitis worldwide.

Annual encephalitis cases nearly 70,000 (half in China) - 10,000 deaths.

ESCMID eLibrary

©

by author

First isolated from a sentinel febrile monkey in 1947 in Uganda.

Symptoms: fever, rash, conjunctivitis, arthralgia.

Fetus: ZIKV specifically attacks neural progenitor cells and causes

microcephaly (also brainstem atrophy, cerebellar hypoplasia, andventriculomegaly).

Among pregnant women with ZIKV infection, birth defects are present in 7% offetuses and infants, particularly if the maternal infection occurs during the 1st

trimester.Adults: Guillain-Barré syndrome is most-infectious complication of ZIKV

infection in adults.

Vector: Aedes mosquitoes (A. aegypti , A. albopictus)

Transmission: mosquito bite, sexual intercourse (of concern due to an

association between ZIKV infection and adverse pregnancy and fetal

outcomes).

Zika virus

ZIKV is the first flavivirus associated with congenital defects including

microcephaly and other birth abnormalities

ESCMID eLibrary

©

by author

Global spread of ZIKV, 2013-2016

ZIKV expanded its geographic range from Africa and Asia to the Pacific Islands,

then further to South and Central America and the Caribbean.

The first large outbreak of disease caused by Zika infection was reported from the

Island of Yap (Federated States of Micronesia) in 2007.

ESCMID eLibrary

©

by author

2011: 17 encephalitis cases (3 fatal) in parts of Australia where cases

had not occurred for many decades. Risk of MVEV encephalitis for the

heavily populated areas of south-eastern Australia.

Vector: Culex spp. mosquitoes

Link between the MVEV activity and environmental factors (record

rainfall, flooding).

Disease: asymptomatic or mild febrile illness (occasionally with rash).

Aprox. 1:150 to 1:1000 infections: encephalitis

Fatality: 15–30%, with long-term neurological sequelae in 30–50% of

survivors

Murray Valley encephalitis virus

The most serious endemic arbovirus in Australia

ESCMID eLibrary

©

by author

Togaviridae

Enveloped single strand, positive sensed RNA viruses

New-world alphaviruses (many highly neurovirulent).

• Eastern equine encephalitis virus: eastern US

• Venezuelan equine encephalitis virus: Central and S. America

Old-world alphaviruses

• Chikungunya virus (CHIKV): sub-Saharan Africa, India,

Southeast Asia, Western Pacific, and recent spread to the

Caribbean and South America

Genus alphavirus

ESCMID eLibrary

©

by author

EEEV - encephalitic form: infants-abrupt onset of neurological signs

older patients a few days after onset of systemic disease.

North American-EEEV: the most deadly encephalitic alphavirus (40%).

Patients that survive the infection may suffer from serious sequelae such as

mental retardation and paralysis.

VEEV: 2–5 days after a mosquito bite.

Children are more susceptible to severe disease than adults and are more

likely to suffer from permanent neurological sequelae.

New World alphaviruses

Although the case fatality rate of VEE is below 1%, its association

with outbreaks involving tens of thousands of human cases renders

it the most important encephalitic alphavirus. ESCMID eLibrary

©

by author

Vectors: Aedes aegypti, A. albopictus

Incubation period: 3–7 d

Symptoms: high fever, headache, maculopapular rash and arthralgia.

During the outbreak in 2005–2006 on Reunion Island, neurological signs were reported in 12% of patients.

Postinfectious complication: Guillain–Barré syndrome

Chikungunya virus

Astrocytes are commonly the first cells activated in brain

Emerging global health threat with increasing incidence of neurological

complications

1952: First isolation from patients with fever and arthralgia

in Tanzania.

Chikungunya = that which bends up

ESCMID eLibrary

©

by author

Phenuiviridae

Single-strand negative-sensed RNA viruses

Sandfly-transmitted phleboviruses

Symptoms: from asymptomatic or mild disease to

meningitis or encephalitis

Neuroinvasive phlebovirus: Toscana virus

Genus Phlebovirus

Vectors: sandflies, mosquitoes, ticks

ESCMID eLibrary

©

by author

Incubation: 3–6 days

Symptoms: mild or self-limited febrile illness (fever, headache, myalgia,

malaise and abnormalities in liver and hematological values, skin rash).

Neurological manifestations: meningitis, paresis, or even

meningoencephalitis or encephalitis.

Toscana virus

Endemic in all Mediterranean countries.

The most common cause of summertime viral meningitis in central Italy

Recent identification of novel strains

Papa et al. EID 2014

ESCMID eLibrary

©

by author

Paramyxoviridae

Nipah virus The most frequent henipavirus

1998: first detection in pig farmers in Malaysia

Host reservoir: fruit bats

Transmission: from human to human via respiratory droplets.

8% of acute encephalitic patients have relapsing encephalitis

Fatality: 30%.

enveloped single-stranded negative-sensed RNA viruses

Genus Henipavirus. Nipah and Hendra viruses

Main site of infection: endothelium of blood vessels in the CNS (and lungs, kidneys) ESCMID eLibrary

©

by author

Zoonotic transmission cycles of Nipah virus in Malaysia and Bangladesh

J Pathol 2015

Zoonotic transmission

through an intermediate,

amplifying host

Direct transmission via the consumption

of date palm sap contaminated with NiV

by fruit bats and further human-to-

human transmission

ESCMID eLibrary

©

by author

First identified in meningitis and encephalitis deaths of a few Australian

individuals who had been in close contact with horses.

Host reservoir: fruit bat.

Amplifying hosts: horses able to transmit the virus to humans who work

closely with infected animals

Incubation: 5–14 days

Hendra virus

Hendra virus infection is an emerging viral disease of horses and humans

in Australia.

Virus transmission

to horses

ESCMID eLibrary

©

by author

small, non-enveloped single-strand positive-sensed RNA viruses

• Genus Enterovirus: poliovirus and the non-polio enteroviruses

• Genus Parechovirus: human parechovirus

Symptoms: common cold to life-threatening infections, such as

encephalitis and myocarditis.

Picornaviridae

ESCMID eLibrary

©

by author

EVs classification into species:

• EV-A, containing EV71 and several Coxsackie A viruses (CV-A)

• EV-B including coxsackie B viruses (CVB) 1–6 and all

echoviruses

• EV-C with the polioviruses (PVs) 1–3 and several CVAs

• EV-D containing EV-68

Enteroviruses

Enteroviruses 71, D-68 and C105 can cause polio-like paralysis

They are considered a critical emerging public health threat

CNS infections are most often caused by EVs

ESCMID eLibrary

©

by author

Typically associated with hand-foot and-mouth disease

Up to 30% of patients demonstrate neurologic complications ranging

from meningitis, encephalitis to a poliomyelitis syndrome in infants

and young children.

Symptoms: fever, mouth ulcers, reduced consciousness, and

irritability and cough, coryza, and vomiting.

Most patients with flaccid paralysis only partially recover, and some of

them show persistent weakness.

Transmission is through the fecal-oral route, through contact with

contaminated secretions and surfaces

Enterovirus 71

It continues to expand its geographic range and has caused

numerous outbreaks in Southeast Asia and Australia

ESCMID eLibrary

©

by author

Incubation: 1-12 days

Transmission: fecal-oral route. Respiratory transmission is also possible

Human parechovirus type 3

First reported in 2004, is exceptional because it can provoke sepsis and

meningoencephalitis leading to neurological sequelae, and even death, in

neonates and young infants

J Pediatric Infect Dis Soc. 2017

• PeV3 can cause severe neurologic illness in neonates. • Younger infants are more likely to require intensive care. PeV3 should be considered along with HSV and other pathogens when evaluating young infants with sepsis-like illness or meningitis.

ESCMID eLibrary

©

by author

single-stranded negative-sensed RNA viruses

Bornaviridae

BoDV-1: causes neurological disease mainly in horses and sheep (i.e.

chronic progressive meningoencephalitis). Highest incidence in central

Europe.

Reservoir: shrews (in Germany Crocidura leucodon).

On 7 March 2018, Germany reported 4 human cases (3 organ

recipients from the same donor) of acute encephalitis linked to BoDV-

1, species Mammalian 1 Bornavirus).

This is the first time that BoDV-1 has been confirmed in humans

Borna Disease virus

ESCMID eLibrary

©

by author

Astrovirus VA1/HMO-C: highly divergent from the classic human

astroviruses; prototype of a distinct evolutionary clade of astroviruses

EID 2010

CID 2015

Astroviridae

Etiologic agent of encephalitis, at least in the context of immunosuppression

ESCMID eLibrary

©

by author

Australian bat lyssavirus

The only virus known to be transmissible to humans directly from bats

without an intermediate host

Zoonotic virus closely related to rabies virus

Three cases of ABLV in humans have been confirmed in Queensland,

all of them fatal.Reservoir: fruit and insectivorous bats

Transmission: bite or scratch of bats

Rhabdoviridae

ESCMID eLibrary

©

by author

Collection and analysis of all available meta-data

Diagnosis of emerging CNS infections:

the syndromic approach

• Demographic data

• Clinical signs and symptoms

• Days after onset of the symptoms

• Place of residence, living conditions, occupation, recreational activities

• Underlying diseases/disorders / comorbidities

• Recent transfusion/ transplantation

• Immune status

• Vaccination history

• Recent travel in endemic areas

• Vector bite history

ESCMID eLibrary

©

by author

Emerging neurotropic viruses are associated with increasedmorbidity and mortality in humans worldwide, representing areal and evolving threat to human health.

It is expected that more novel pathogens will be identified inthe near future (broader application of NGS)

Early recognition of the causative agent of unexplained acuteCNS infections will enable specific interventions to preventoutbreaks that threaten public health.

The facts

ESCMID eLibrary

©

by author

• Clinicians should be aware of emerging CNS infections and

include them to the differential diagnosis

• Microbiologists should have ready lab protocols for prompt

and correct diagnosis (EQAs are helpful)

• Awareness of the public (living in or travelers to endemic

areas - special attention to pregnant women and ZIKV

transmission).

• There is need for effective surveillance and control and for

drugs and vaccine design.

Actions needed

ESCMID eLibrary

©

by author

ESCMID eLibrary

©

by author