COMMON INFECTIOUS DISEASES IN LABORATORY RATS AND MICE

1. COMMON INFECTIOUS DISEASES IN LABORATORY RATS AND MICE

2. What’s common? • Helicobacter spp. – 15% • C. bovis – 3% • Pneumocystis carinii – 2% • Pinworms – Mouse – 0.3% Rat – 1.3% • Mites – 0.1% (mice only) • MHV – 2% • Parvoviruses • Mouse – 2% • Rat – 4% • EDIM – 0.7% • Norovirus ~30% • RRV – 7%

3. What’s common in mice?

4. What’s common in rats?

5. Mouse Hepatitis Virus(MHV) • Coronavirus, ss RNA, enveloped • Very high evolutionary capacity (innumerable strains) • Prevalence moderate • Virus 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

6. 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

9. Enterotropic MHV • Strains: D, RI, Y, G, myriad others. • Most wild type strains are enterotropic • Clinical signs and gross lesions rare in immunocompetent adult mice • Primary replication: • GI tract, especially distal ileum, cecum, ascending colon • Secondary sites - uncommon • Clearance mediated by B cells • Not cleared in μMT mice (anecdotally also in many GM lines) • Dissemination prevented by T cells • Disseminates in TCR βδ- , IFN-γ- , RAG1, athymic nude mice

10. Research Impact of MHV • Prolonged immunologic effects: • NK cells, T-cells, B-cells • Infects monocytes, macrophages, bone marrow dendritic cells • Delayed allogeneic graft rejection • Alters course of concurrent infections, such as Helicobacter hepaticus

11. 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

12. 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

13. CONTROL OF MHV • Immunocompetent 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

14. Parvoviruses Are you getting mixed signals on parvoviruses?

15. 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

16. 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.

17. 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) • Immunity • In vitro reduction of T-cell response by MMVi and in vivo late reduction of cytotoxic memory cells by MMVp • Cytoskeleton • In vitro (A9 cells) dysregulation of gelsolin (↑) and WASP (↓) by MMVp • Tumor studies • MMVp is oncotropic and oncolytic in some human tumors (hemangiosarcoma) and mouse tumors

18. Parvoviruses of Mice • Mouse Parvovirus (MPV-1, MPV-2, MPV-3, MPV-4) • Prevalence higher than MMV • Causes persistent infection • No anatomic lesions, even in scid mice • Different 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 dose • DBA/2 only slightly better

19. Research Effects of MPV • MPV-1a (cell culture adapted) modulates immune response (McKisic et al, 1996) • Suppression of T cell response in vitro • CD8+ 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

20. Detection of Parvoviruses • Serology – Usually best for screening • MFIA or ELISA - Traditional or recombinant antigens • Use panel of antigens for each serotype, plus the generic NS-1 antigen • Mice - 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!

21. 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

22. 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

23. Control of Parvoviruses • Can not “burn out” because infection is persistent • Can 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 embryos • No envelope, so it stays active in environment • Must thoroughly disinfect environment, materials and equipment with oxidizing agent (Clidox, ozone, etc.)

24. Exclusion of Parvoviruses • Consider sources of research animals: • Vendors, GM animals, immunodeficient • Wild rodents • Biological materials • Risk from personnel handling infected rodents (pets, snake food) • Fomites (Feed, bedding, water, used/shared equipment etc.)

25. Noroviruses • Type 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

26. 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

27. 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

28. 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

29. 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

30. 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.

31. 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