COMMON INFECTIOUS DISEASES IN LABORATORY RATS AND MICE

What’s common?

•MHV – 2%

•Parvoviruses

•Mouse – 2%

•Rat – 4%

•EDIM – 0.7%

•Norovirus ~30%

•RRV – 7%

•Helicobacter Helicobacter spp. – spp. – 15%15%

•C. bovis – 3%C. bovis – 3%

•Pneumocystis carinii – Pneumocystis carinii – 2%2%

•Pinworms – Pinworms – Mouse – 0.3%Mouse – 0.3%Rat – 1.3%Rat – 1.3%

•Mites – 0.1% (mice Mites – 0.1% (mice only) only)

What’s common in mice?Agent Assay # tested # pos. % pos.

Parv NS-1 ELISA 445,255 8,481 1.9048%

MPV ELISA 457,062 8,974 1.9634%

MVM ELISA 458,931 1,789 0.3898%

MHV ELISA 441,098 7,949 1.8021%

EDIM ELISA 364,793 2,459 0.6741%

GDVII ELISA 342,312 991 0.2895%

MPUL ELISA 352,563 32 0.0091%

REO ELISA 338,054 43 0.0127%

SENDAI ELISA 361,118 10 0.0028%

PVM ELISA 353,043 12 0.0034%

What’s common in rats?

Agent Assay # tested # pos. % pos.

RPV ELISA 73,289 1,324 1.8065%

H-1 ELISA 67,594 1,128 1.6688%

KRV ELISA 73,400 1,136 1.5477%

RMV ELISA 29,110 437 1.5012%

GDVII ELISA 28,203 264 0.9361%

SDAV ELISA 68,445 159 0.2323%

MPUL ELISA 67,951 127 0.1869%

M pulmonis Culture 3,558 2 0.0562%

PVM ELISA 66,450 98 0.1475%

SENDAI ELISA 67,193 16 0.0238%

REO ELISA 61,016 5 0.0082%

Mouse Hepatitis Virus(MHV)

Coronavirus, ss RNA, envelopedVery high evolutionary capacity (innumerable

strains)Prevalence moderateVirus types grouped as enterotropic

(intestinal) or polytropic (multiple tissue) – most field strains are enterotropic

Clinical signs very rare in immunocompetent mice after weaning

Wasting syndrome in many immunodeficient mice

MHV

As enveloped virus – does not persist in environment. Probably not infective after 48 hrs.

Short-term transfer by fomites (sleeves, equipment, bedding)

Highly contagious and can spread rapidly

Enterotropic MHV

Strains: D, RI, Y, G, myriad others .Most wild type strains are enterotropicClinical signs and gross lesions rare in

immunocompetent adult micePrimary replication:

GI tract, especially distal ileum, cecum, ascending colonSecondary sites - uncommonClearance mediated by B cells

Not cleared in μMT mice (anecdotally also in many GM lines)

Dissemination prevented by T cellsDisseminates in TCR βδ- , IFN-γ - , RAG1, athymic nude

mice

Research Impact of MHV

Prolonged immunologic effects:NK cells, T-cells, B-cellsInfects monocytes, macrophages, bone marrow dendritic cellsDelayed allogeneic graft rejection

Alters course of concurrent infections, such as Helicobacter hepaticus

MHV Detection

Serology

Excellent cross-reaction among strains

MFIA or ELISA, with IFA for confirmation

Seroconversion within 2 weeks (often one week)

Histopathology

Lesions should by confirmed by IHC, PCR or serology

MHV Diagnosis

PCR

Sequencing of PCR product (nucleocapsid gene) for epidemiology

Fecal Shedding (quarantine, immunodeficient mice)

Environmental

Confirmation of serology by PCR of mesenteric lymph nodes

CONTROL OF MHVImmunocompetent mice self-cure

Enveloped virus: not stable in environment, easy to disinfect

Can eliminate from immunocompetent colonies by not breeding and no new mice for 6-8 weeks (test 1st)

Infection persists in immunodeficient mice

Are you Are you gettinggetting mixed signals on mixed signals on

parvoviruses?parvoviruses?

Parvoviruses

Parvoviruses in Mice

ssDNA, non-enveloped

Virus remains active in environment

Resistant to desiccation and many (non-oxidizing) disinfectants

Fairly common

Generally no clinical signs

Cause persistent infection – no self-cure

Need actively dividing cells to replicate

Parvoviruses of Mice

Mice Minute Virus (MMV or MVM) Multiple strains (i, p, c, m), MMVm is most prevalent and is persistent. Others are

culture-adapted strains.MMVm reported to cause stunting, low reproduction and early deaths in NOD μ-chain KO

mice .

Experimentally, caused hronic progressive infection in scid mice.

Research Effects of MMV

Cell culture Can infect many mouse cell lines, as well as some rat

embryo lines and transformed human cells (324K, EL-4)

ImmunityIn vitro reduction of T-cell response by MMVi and in

vivo late reduction of cytotoxic memory cells by MMVp

CytoskeletonIn vitro (A9 cells) dysregulation of gelsolin (↑) and

WASP (↓) by MMVp

Tumor studiesMMVp is oncotropic and oncolytic in some human

tumors (hemangiosarcoma) and mouse tumors

Parvoviruses of Mice

Mouse Parvovirus (MPV-1, MPV-2, MPV-3, MPV-4) Prevalence higher than MMVCauses persistent infectionNo anatomic lesions, even in scid miceDifferent strains not very cross-reactive by ELISA,

MFIA

C57BL/6 mice and congenic strains partially resistant to infection

C57BL/6 mice require 10-100x infective doseDBA/2 only slightly better

Research Effects of MPV

MPV-1a (cell culture adapted) modulates immune response (McKisic et al, 1996)

Suppression of T cell response in vitroCD8+ T lymphocyte clones lose function and viability

Cytokine- and antigen-induced T cell proliferation in vitro suppressed after exposure to MPV-1a

Potentiates allograft rejection in vivo

GEM expressing B19 NS1 have altered immune system and high fetal mortality resembling non-immune hydrops fetalis

Detection of Parvoviruses

Serology – Usually best for screeningMFIA or ELISA - Traditional or recombinant antigens

Use panel of antigens for each serotype, plus the generic NS-1 antigenMice - MMV, MPV-1, MPV-2, and NS-1

Rats - RV, H-1, RPV, RMV and NS-1

IFA – Good follow-up assay for positive/equivocal MFIA/ELISA

Be careful with MPV serology of C57BL/6 mice!

Detection of Mouse Parvoviruses

PCR

Can be strain-specific (VP2) or generic (NS-1)

Mesenteric LN stay positive indefinitely

Pooled fecal samples to detect shedding (Beware of fecal inhibitors of PCR)

Biologicals and cell cultures

Environmental swabs

Detection of Mouse Parvoviruses

Many Challenges (sentinel parvovirus)

Some strains partially resistant (C57BL/6, DBA/2)

Not all mice may seroconvert to all antigens (NS-1)

May have very low prevalence in IVC and filter-top caging (hard to sort out from false positives)

Seroconversion generally within 7 days, but may be slow in adults exposed to low infectious dose

Control of Parvoviruses

Can not “burn out” because infection is persistentCan only eliminate by rederivation

If caesarian section, must carefully test offspring and foster dams. Primaparous dams more likely to be

viremic.Reported as detected from sperm and pre-implantation

embryosNo envelope, so it stays active in environment

Must thoroughly disinfect environment, materials and equipment with oxidizing agent (Clidox, ozone, etc.)

Exclusion of Parvoviruses

Consider sources of research animals:Vendors, GM animals, immunodeficient

Wild rodentsBiological materialsRisk from personnel handling infected rodents (pets, snake food)Fomites (Feed, bedding, water, used/shared equipment etc.)

NorovirusesType virus is Norwalk virus, “cruise ship

virus”Non-enveloped, RNA

Cause >90% nonbacterial epidemic gastroenteritis worldwide, 23M cases/yr in

US (per CDC)

Cruise ships, institutions, military

Noroviruses

MNV

Genetically distinct (genogroup V) from human noroviruses (I, II, IV), zoonotic spread unlikely

No evidence of clinical disease or lesions in immunocompetent mice

No noroviruses yet reported in other lab rodents

MNV-1

No disease in immunocompetent mice

High mortality in RAG (-/-) STAT (-/-)double KO mice, with disseminated infection and encephalitis and pneumonia

Encephalitis only with IC inoculation

MNV

Many variants isolated at this point, > 50 at CRL

MNV widespread in lab mouse research facilities

No clinical disease reported in natural infections

Most major vendors (including CRL) reporting all colonies negative for MNV by serology

and/or PCR

MNV

Research interference unknown, but:MNV-1 was detected in macrophage-like cells in vivo and grew in vitro in

dendritic cells and macrophages. Growth was inhibited by the interferon αβ receptor and by STAT-1 (Wobus et al., 2004)

Possible macrophage aggregates in RAG livers

MNV

Diagnosis:MFIA/ELISA – recombinant capsid protein self-assembles into VLP. Good cross-

reaction among variants

PCR – Virus shed in feces for long periods, should persist in environment. PCR must be properly designed to be able to detect multiple strains .

MNV

Management

Virus probably present in mice for a long time (so no hurry)

Nonpathogenic

Widely distributed

Numerous strains

Noroviruses should not cross placenta, so c-section or ET rederivation should be successful

Must consider environmental decontamination