Rift Valley fever virus: Diagnosis and vaccines

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Presentation by Dr Kariuki Njenga of the Centers of Disease Control & Prevention, at the Enhancing Safe Inter-regional Livestock Trade held at Dubai, UAE, 13-16 June 2011.

Presentation by Dr Kariuki Njenga of the Centers of Disease Control & Prevention, at the Enhancing Safe Inter-regional Livestock Trade held at Dubai, UAE, 13-16 June 2011.

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  • 1. Rift Valley Fever Virus: Diagnosis and Vaccines M. Kariuki Njenga, BVM, PhD Centers for Disease Control and Prevention Nairobi, Kenya
  • 2. RVF Virology RVF virions (Neg stain) Virions in hepatocytes By Geisbert TW, USAMRIID, MD. G1,G2vRNA S 1690 nt M 3885 nt 271 nt L 6404 nt NP NSs untranslated (245aa) (264aa) [26 kDa] [17 kDa] NSm G1 G2 (135 aa) (534aa) (507aa) RdRp [14 kDa) [58 kDa] [56 kDa] (2092 aa) [237 kDa] NSm NP  Not essential for virus replication  Most abundant component of virion  Shown to suppress virus-induced apoptosis in vitro  complexes vRNA in virion, cRNA in infection  Other functions unknown Needed for virus replication + packaging  recN ELISA good diagnostic tool G1, G2 NSs  Envelope surface glycoproteins  Not essential for virus replication  Integral membrane proteins  Blocks production of interferon in vitro  Involved in virus attachment and tissue tropism  Essential for virulence  Targets of neutralizing antibodies
  • 3. Laboratory Diagnosis – RVF Case ConfirmationSpecimen: Serum, whole blood, liver tissue, aborted fetusTests performed: VI, antigen ELISA, PCR, IgM sandwich ELISA, IgG ELISA, VN
  • 4. Biosafety in diagnosis There is no vaccination for humans – Reduce the risks! • Special caution when doing PM’s • Inactivate the sample within the 1st step • Handling of lab specimen (let serum clot....) • Reduce pipetting and dilution steps • Wash plates and equipment with caution • Wear PPE
  • 5. Laboratory Quality AssuranceSuccessful diagnosis depends largely onthe quality of the specimen and the transportand storage conditions of the specimen beforeit is processed in the laboratory
  • 6. Strategies for diagnosis of RVFBased on detection of:  Live virus  Viral antigens 1 – 10 days  Viral nucleic acids  Acute phase antibodies (IgM) 4 – 42 days  Chronic phase antibodies (IgG) 7 - ?days
  • 7. Short viremia following RVF infection• Data shows that 1010 RNA copies/mL of serum in sheep and 108 copies/mL in cattle and humans• At day 9 post-infection, calves no longer viremic, and RVF virus can be isolated only from the brain.
  • 8. RVF Diagnosis  during outbreak  post-outbreak  for routine surveillance*  for return to trade  sentinel animals*For routine surveillance - is the region endemic or RVF-free? - has there been vaccination?
  • 9. RVF Diagnosis (Endemic Region)During outbreak and post-outbreak - PCR, antigen and IgM - Send samples for virus isolation - IgG NOT usefulFor returning to trade after outbreak - PCR, antigen and IgM - Send samples for virus isolation - IgG NOT useful
  • 10. RVF Diagnosis (Endemic Region)For routine surveillance - IgM, IgG for animals born in IEP - Send samples for virus neutralizationFor sentinel animals - IgM, IgG - Send samples for virus neutralization
  • 11. RVF Diagnosis (RVF-free Region)- IgG sufficient- May do both IgM and IgG for confirmation- Send samples for virus neutralization
  • 12. Antibody profile in infected vs vaccinated IgG IgM InfectedVaccinated Paweska , J Virol Methods. 2003
  • 13. RVF SeroprevalenceDomestic animals – Cattle, sheep goat sandwich/indirect EIA, VN – Camel inhibition EIA, VNSentinel animals – Sheep sandwich/indirect EIA, VNWildlife – Buffalos + others inhibition EIA, VNVaccination NONE
  • 14. Available testCommercially:– BDSL..... inhibition ELISA for detecting IgG (in all species). capture ELISA for IgM (in specified species, bov. capr. ovi) indirect ELISA for IgG (anti-species conjugate) Sandwich ELISA for IgG (in specified species, bov. capr. ovi)Through research links– CDC/USA (S. Nichol) - not available commercially– USDA/USA (W. Wilson) – still undergoing validation– NICD/RSA (J. Paweska) – most available through BDSL
  • 15. RVF Vaccines: Situations and controlapproaches RVF Situation Examples of countries Current Control Strategy Endemic with regular Kenya, Tanzania, Vaccination at sign of outbreak outbreaks Egypt, Senegal, Mali Egypt: continuous vaccination No vaccination Endemic with sporadic/re- South Africa, Saudi Arabia Continuous/yearly vaccination occuring outbreaks Free high risk Middle East, North Africa (Active) surveillance Free low risk Europe, Americas Surveillance, talks of vaccine banksLimited continuous vaccination of livestock in Africa: • Cost of yearly vaccination • Safety concerns: difficulties to determine physiological stages of pregnant animals • Irregularity of outbreaks (years without signs of outbreak) • Policy aspects: vaccination not always covered by government Courtesy: Baptiste Dungu, GALVmed
  • 16. Ideal RVF vaccine (Product profile)…• Generic characteristics • Endemic regions – Safety – Continuous vaccination: yearly • Safe to produce vaccination of susceptible livestock • Safe to all physiological stages of animals • Need to know how many vaccinations • No residual virulence may be required to build a life long • No risk of introduction into the environment (shedding, immunity persistence in animals etc.) • No risk of spread to human or other species – Efficacy • Solid protective immunity after 1– Efficacy vaccination • Protection of all susceptible species • Quick onset of protective immunity, including in young animals • Long lasting immunity • Free regions • STOP TRANSMISSION: prevent amplification of RVFV • Quick onset of protective immunity in ruminants • Protective in young animals and possibly– Vaccination newborn naïve animals • Cost effective for producers and users • Sterilizing immunity • Single vaccination • DIVA • Ease of application • Suitable for stockpiling (vaccine or antigen bank) and quick availability Courtesy: Baptiste Dungu, GALVmed
  • 17. Vaccination strategies to be considered Endemic regions  Free regions/ Prevent epidemics – Yearly vaccination – Elimination of possible source of re-infection - Intermittent multiyear vaccination* – Use of non-replicating antigen vaccine – Multivalent or combination vaccine, – Early and rapid onset of immunity, even in consisting of RVF antigen & antigen of a young animals vaccine likely to be used regularly RVF+LSD; RVF+ s/g pox; RVF + CBPP  DIVA – Thermostability – Positive marker: export of animals from – Use of sentinel animals: need for good endemic countries diagnostics capability & effective – Negative marker: for detecting infection – Role of veterinary services  Possible suitable candidates: Possible suitable candidates: – Replication deficient, deleted, marker vaccine – Multivalents including a safe deleted RVFV vaccine Set up regional vaccine bank - FAO/ NGO/Private company - Need storage facility Suitable vaccination strategies more critical than improved vaccines Modified from: Baptiste Dungu, GALVmed
  • 18. RVF traditional vaccinesVACCINE STRAIN ADVANTAGES DISADVANTAGESInactivated Pathogenic ● Safe in pregnant ● Short term immunity(OBP, VSVRI) field strain animals ● Multiple vaccinations required ● Can be used in ● Risk of handling virulent strain during outbreak production ● Colostral immunity present but poor ● Sheep better protected than cattle ● 100 x more antigen required than for live attenuated ● Longer production lead timeLive Smithburn ● Highly immunogenic ● Potential residual virulenceAttenuated (OBP, ● Single dose ● Teratogenic for foetusKEVEVAPI) ● Good immunity ● Potential risk of reversion to virulence (within 21days) ● Not advisable for use in outbreaks ● Effective and easy ● Theoretical possibility of transmission L production by mosquitoes (?) ● Safer production ● Large batches: >4m S doses Courtesy: Baptiste Dungu, GALVmed
  • 19. New candidates evaluated in target animalsVACCINE STRAIN ADVANTAGES DISADVANTAGESLive MP12 ● Effective and good protective ● Teratogenic for foetusattenuated immunity ● Abortion in early pregnancy ● Easy and safe to produce ● Not available commercially ● Better safety than Smithburn in most species and age groupsAvirulent Clone 13 ● Good protective immunity in ●Only registered to date in Southnatural sheep & cattle Africa & Namibiamutant ● Safe in pregnant animals ●large scale field data in other regions ● Safe in outbreak needed ● Produced as standard freeze- ●No evidence of DIVA to date dried live vaccine ● Safe, effective and easy to produce ● Possible DIVA (NSs ELISA?) ●Registered 7 used extensively in South AfricaRecombinant LSD ● Dual vaccine ● Only proof of concept to dateLumpy skin Neethling ● Safe in all animals ● Currently grown in primary cellsvirus strain ● DIVA ● Possible GMO regulation challengeexpressing expressing ● Long shelf life (LSD) (?)RVF RVF ● More thermo-tolerant than others glycoproteins ● Efficacy shown in animal trials
  • 20. RVFV clone 13 deletion RNA segments Proteins Nucleocapsid protein (N)Large (L) Viral RNA polymerase (L)Medium (M)Small (S) Glycoprotein G1 Glycoprotein G2 NSm 14 & 78 KDa NSs 100 nm Courtesy: Baptiste Dungu, GALVmed
  • 21. Clone 13 sheep efficacy data Experiment 3: average temperature per group post-challenge 42 41 40 39 38 37 36 35 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 3A Early Chall 3A Late Chall 3B Early Chall 3B Late Chall 3C Early Chall 3C Late Chall Early Chall control Late Chall Control Dungu et al., 2010
  • 22. Clone 13 cattle efficacy data Mean Body Temperature 41.5Mean Body Temperature 41 Body Temp (Deg. C.)for each group through theviral challenge phase. DPC: 40.5Days post-challenge. 40 39.5 Vaccinated Group 39 Control Group 38.5 38 37.5 37 0 3 6 9 -3 12 15 18 21 24 27 Days Post- challengeClinical course for the unvaccinated control group Animal ID Peak Fever Day PC Duration of Euthanasia fever 1367 41.2 3 8 days (2-9) 9 1402 41.4 2 1 day (2) 3 1404 41.0 2 7 days (2–8) 11 1405 41.3 2 1 day (2) 3 1406 40.4 2 3 days (2-4) 11 Dungu et al., In Submission
  • 23. Candidates not evaluated in target animalsVACCINE STRAIN ADVANTAGES DISADVANTAGESAvirulent (lab R566: deletion in ● Safer due to deletions in all 3 ● Never tested in target animalsgenerated) the M and S segments, may never reassort ● More stringent regulatoryreassortant segments ● Protection in mice requirements for registration (?)Virus- Canarypox- ● DIVA: Positive & Negative ● No registered vaccine yet availablevectored RVF expressing RVF marker ● No large scale field data yetvaccines proteins ● Live vaccine available, although extensive ● Replication deficient analytical data generated Heterologous ● Multivalent: suitable where ●Data to date showing low virus expressing annual vaccination is a challenge immunogenicity GP: Newcastle ● Potential for improved disease virus as thermostability vectorVirus like VLP made of ● Potentially very safe ● No proof of concept in targetparticle (VLP) envelop proteins ● Immunity similar to live vaccine, animals (GP) but no replication ● Large scale production might be a Naslund et al., ● DIVA challenge 2009DNA DNA priming + ● DIVA ● Only incomplete protection inact. Vaccine ● Potentially long lasting demonstrated in mice Lorenzo et al., immunity ● Production challenges 2009 ● Ability to enhance and modulate ● Regulatory challenges (use in food induced immunity animals) cDNA encoding GP
  • 24. New Candidate…VACCINE STRAIN ADVANTAGES DISADVANTAGESRecombinant- ● Reverse genetic ● Less prone to reassortment ● Not yet registeredmultiple generating RVF ● Live vaccinedeletion virus virus with double ● DIVA: negative marker deletions in NSs & ● Easy and safe to produce NSm Bird et al., 2008 ●Target animal efficacy & safety data generated RNA segments Proteins Nucleocapsid protein (N) Large (L) Viral RNA polymerase (L) Medium (M) Small (S) Glycoprotein G1 Glycoprotein G2 NSm 14 & 78 KDa 100 nm NSs Courtesy: Baptiste Dungu, GALVmed