Epidemiology of Adenovirus Infections

1. Epidemiology of Adenovirus Infections • Ubiquitous DNA viruses • Cause 5 -10% of febrile illnesses in early childhood • Nearly all adults have Abs to endemic serotypes 1, 2, 5, or 6

2. Clinical Manifestations • Vary according to the age and immune status of host • Different serotypes are associated with distinct syndromes

3. Adenovirus Transmission • Easily transmissable to individuals w/o serotype-specific Ab • Specific epidemic serotypes • Pharyngoconjunctival fever in summer camps, public swimming pools – Ad3, Ad7 • Hemorrhagic keratoconjunctivitis in medical facilities – Ad8, Ad37 • Acute respiratory disease in military recruits – Ad4, Ad7 • Minimal infectious dose?

4. Adenovirus Pneumonia • Adenoviruses cause about 10% of pneumonias in healthy children – Ad3, 7 • Disease more severe in infants • Extrapulmonary symptoms may occur w/o viral-specific histopathology • Meningoencephalitis, hepatitis, myocarditis, nephritis, neutropenia, DIC • Toxin?, Immune-mediated?

5. Adenovirus Infections in Immunocompromised Hosts • Range from asymptomatic shedding to fatal disseminated disease • Disease may result from • Primary infection • Reactivation of infection in patient • Reactivation of infection in donor organ

6. Adenoviruses in Bone Marrow Transplant Recipients • Wide range of clinical syndromes • Pneumonia • Gastroenteritis, hepatitis • Hemorrhagic cystitis, nephritis • Encephalitis, myocarditis • Incidence of infection higher in children vs. adults

7. Adenovirus disease in BMT recipients • Mortality of invasive disease 50 -60% • Risks factors for invasive disease • Allogeneic transplants • especially T-cell depleted transplants • GVHD • 2 or more culture-positive sites

8. 1985 Seattle Study • Reviewed 1051 BMT recipients • Patient characteristics • Most had unmodified grafts from related matched donors • Proportion of children not stated • Incidence of adenovirus infection 5% • 1% incidence of disease (10) • mortality 50%

9. 1994 Milwaukee Study • Reviewed 201 BMT recipients • Patient characteristics • 85% T-cell depleted grafts • 50% unrelated or partially-matched donors • 40% children • Incidence of adenovirus infection 21% • 6.5% incidence of disease (13) • mortality of disease 54%

10. 1994 Milwaukee Study • Higher incidence of adenovirus infections in children • 31% vs. 14% in adults • Earlier time of onset in children • mean <30 days vs. >90 days in adults • Ad35 and endemic types were most common isolates

11. 1999 Kentucky Study • Reviewed 532 BMT recipients • Patient characteristics • 72% allogeneic • 40% T-cell depleted • 24% children • Incidence of adenovirus infection 12% • Higher in children 23% vs. adults 9% • Incidence of disease 7.7% (41) • Overall mortality 73%

12. 2000 Bristol Study • Reviewed 572 BMT recipients • Patient characteristics • 45% had T-cell depleted grafts • 45% unrelated donors • 2/3 children • Incidence of adenovirus disease 17% (100) • Incidence of infection not documented • Definition of disease not vigorous • Mortality much lower than other studies - 6%

13. Solid Organ Transplantation • Adenovirus infection usually involves donor organ • Hepatitis in 3% pediatric liver transplants • Mortality 50% • Pneumonia in 1% lung transplants • Hemorrhagic cystitis in 1% renal transplants • Mortality <20%

14. Congenital Immunodeficiency Syndromes • SCID patients may develop severe infections • Mortality 50% • Pneumonia and hepatitis are most frequent syndromes • Patients with Ig deficiencies have less severe but more protracted illnesses

15. Adenoviruses in AIDS Patients • Adenoviruses frequently isolated in stool and/or urine w/o symptoms • Case reports of fatal infections including • Hepatitis, pneumonia, encephalitis, nephritis

16. Adenoviruses in Cancer Patients • More common in children than adults • Case reports of fatal infections including • Pneumonia, hepatitis, encephalitis, nephritis

17. Treatment • Discontinue immunosuppressive therapy • No antiviral documented to be of benefit • Cidofovir has best in vitro activity

18. Cidofovir • Broad spectrum nucleoside mono-phosphate analog • Inc. HSV, VZV, CMV, EBV, HHV-6, HPV • Has in vitro activity against adenovirus • However resistance may develop • Active in rabbit eye model

19. Therapy • Case reports • Hemorrhagic cystitis in BMT pts • response to IV ribavirin or vidarabine • Ad7 colitis in unrelated donor recipient d37 • No response to IV ribavirin. • Sx resolved on cidofovir w/i 2 wks. • Ad colitis and cholecystitis in AIDS pt • Prompt improvement with cidofovir

20. Immunotherapy • IV IgG may be helpful for lower serotypes • Most preps have good titers of neutralizing antibodies • Case report using donor lymphocytes in BMT recipient

21. Immune Responses Against Adenoviruses • Cell-mediated immunity • Severe infections occur primarily in hosts with cellular immune defects • Humoral immunity • Neutralizing antibodies protect against re-infection with same serotype • By age 10, most have Ab to endemic types

22. Adenovirus-specific T cell Responses • Most healthy adults have detectable proliferative and cytotoxic memory T cell responses • Adenovirus-specific T cells recognize epitopes conserved across different serotypes • In contrast to serotype-specific neut. Abs

23. Pathogenesis • Direct lysis of susceptible cells • Immunopathology? • Persistence

24. Adenovirus Persistence • Isolated from tonsils in asymptomatic children • Shed in stool for months post-infection • Cases of transmission from donor organs • Cases of reactivation in BMT patients

25. Transmission of adenovirus from solid organ transplants • Cases reports • Renal transplant pts with Ad34/35 hemorrhagic cystitis • documented seroconversion to Ad34/35 c/w with transmission from donor kidney (or primary infection) • Pediatric liver transplant pts with Ad5 hepatitis • 6/9 seronegative pre-transplant; donors Ab pos • Median time of onset 25 days

26. Reactivation of adenovirus in BMT recipients • Cases reports • Ad5 hepatitis • Ad5-specific neutralizing Ab present in pre-transplant sera • c/w reactivation of endogenous virus • Ad35 cystitis, nephritis, colitis • 6/6 adult pts had neutralizing Ab to own isolate pre-transplant (PF data)

27. Mechanism of Persistence • Remains episomal in long-lived lymphocytes? • Ad types 11,34,35 may establish persistence more readily • Infect hematopoietic cells more efficiently than other serotypes • Low level replication in tissue? • Integration?

28. Adenovirus Early Region 3 • E3 region codes for proteins that inhibit host responses • Down-regulate MHC class I antigens • Inhibit lysis by tumor necrosis factor • Inhibit apoptosis by Fas • Reduces immunogenicity? • Facilitates persistence?

29. Adenovirus Persistence • Reservoirs? • Lymphoid tissue • tonsils • Peyer’s patches in gut • Kidney • Liver • Lung, brain – PCR data

30. Are Lymphocytes a Reservoir? • Old data that PBMC from most donors positive for Ad2 by Southern blot • Not confirmed when assayed PBMC by PCR for Ad2 DNA • Used nested primers to E1A and hexon • 72 of 73 asymptomatic children and adults were negative

31. Adenovirus Reservoirs • Lung • Detected E1A by PCR in 20/20 biopsies from lung cancer pts • Detected E1A by ISH in 2 pts • Detected E3 DNA by PCR in 10 pts • Authors suggest E1A may integrate into host DNA • Brain • Detected E1A in brain microglial cells by ISH and immunohistochemical staining in 7/7 senile pts • No negative controls

32. Live Adenovirus Vaccine • Live type 4 and type 7 vaccines used for years in military • Enteric-coated for oral administration • Safe and effective • Example of safety of RCA • via oral route • in healthy military population

33. RCA in Adenovirus Gene Therapy Vectors • Minimal infectious dose unknown • Likely dependent on multiple factors inc. • Route of administration • Presence or absence of serotype-specific Ab • Severity of disease dependent on: • Route of administration • Status of cellular immunity • Serotype

34. RCA in Adenovirus Gene Therapy Vectors • Elimination of RCA from E1-deleted vectors may be feasible • Altered 293 cell lines have been developed that prevent E1 recombination events • “Gutted” or helper-dependent vectors • Must purify away from E1-deleted helper adenovirus and RCA

35. Issue of Recombination • Recombination of E1-deleted vectors may occur in vivo with • persistent adenoviruses • newly acquired adenoviruses • Clinical significance?