Spf and spr
- 1. Principles of SPF and SPR Presented by R. Bharathi Rathinam
- 2. SPF • SPF status is gained by specific management conditions where pathogens are excluded from the culturing facilities. • This is a common strategy for domestication programs. • SPF animals are free of one or more specific pathogens, but this health status does not refer to their susceptibility to infection or disease. • In addition to being SPF, animals may or may not also be resistant or tolerant to the same or other pathogens.
- 3. Non-SPF broodstock • There are many problems involved with the use of non-SPF broodstock. • The first and foremost has already been discussed which is the possibility of importing novel pathogenic viruses and other diseases into new or clean areas. This has already been seen in Asia with the introduction of P. vannamei into Mainland China, Taiwan Province of China and Thailand. • The problem here is that non-SPF shrimp tend to be cheaper and more easily available (pond-reared broodstock in Asia currently sell for US$8–10, while SPF broodstock from Hawaii cost US$23–25 delivered) and are hence initially attractive, but may have long-term negative consequences.
- 4. • In addition, without strict biosecurity and disinfection protocols for treating non-SPF broodstock, eggs and nauplius, any pathogens infecting the broodstock tend to be passed to the larvae which increases the possibility of serious disease problems during on-growing. • Another problem is that it is extremely difficult to ascertain whether the stocks bought in are really SPF or not. Often competent testing facilities do not exist in Asian countries and many unscrupulous dealers will sell supposedly SPF stocks with false certificates to unwary farmers. • A final problem is that while SPF stocks are almost certainly domesticated lines which have been selected for growth and disease resistance over a long period, non-SPF stocks may not have been selected and are of often uncertain parentage. This makes their use as founder populations for genetic selection and domestication programmes undesirable.
- 5. INTRODUCTION • The status of Specific Pathogen Free should signify that the shrimp have passed through a rigorous quarantine and disease screening process that determined them to be free from specified pathogens of concern to culturists.
- 6. • This characteristic means that countries or regions which still do not have this species can be reasonably sure that the importation of SPF animals will not result in the introduction of the specified pathogens for which the animal is declared “free”. • This does not, however, guarantee against the animal being infected with unknown pathogens or known pathogens which are not screened against.
- 7. • Genuine SPF shrimp are those which are produced from biosecure facilities, have been repeatedly examined and found free of specified pathogens using intensive surveillance protocols, and originate from broodstock developed with strict founder population development protocols. • These founder populations are generated by extensive quarantine procedures that result in SPF F1 generations derived from wild parents (Lotz, 1997). Only when raised and held under these conditions you can have true SPF stocks.
- 8. • Once the animals are removed from the SPF production facilities, they should no longer be referred to as SPF, even though they may remain pathogen free. Once outside the SPF facility, the shrimp may be designated as High Health (HH) as they are now subject to a greater risk of infection, but only if they are placed into a well-established facility with a history of disease surveillance and biosecurity protocols.
- 9. • If the shrimp are put anywhere else, for example into a non-biosecure maturation unit, hatchery or farm, they can no longer be called SPF or HH as they are now exposed to a high risk of infection. • The primary goal of SPF facilities is to produce strains of shrimp that are disease-free, domesticated and genetically improved for aquaculture. Example : P. vannamei and P. stylirostris.
- 10. Drawback of SPF • One potential drawback of SPF animals is that they are only SPF for the specific diseases for which they have been checked. • Typically this will consist of the viral pathogens which are known to cause major losses to the shrimp culture industry, including WSSV, YHV, TSV, IHHNV, BPV and HPV as well as microsporidians, haplosporidians, gregarines, nematodes and cestodes. • Despite this screening, new, hidden or “cryptic” viruses may be present, but because they are as yet unrecognized, may escape detection. Thus, it is believed that SPF shrimp shipped from Hawaii resulted in the contamination of shrimp in Brazil and Colombia with TSV (Brock et al., 1997). This was because, at the time, TSV was not known to have a viral cause and therefore went unchecked in SPF protocols.
- 11. • Additionally, new diseases may emerge from mutations of previously non-pathogenic organisms - i.e. the highly mutable RNA viruses. • Hence, it remains a possibility that importation of SPF shrimp may not rule out simultaneous importation of pathogens. Another possibility is that if SPF shrimp are stocked into facilities with high viral loads, substantial mortality can result as they are not necessarily more resistant to these diseases than non-SPF shrimp, and in some cases, less so. • They may thus be more suited to culture in biosecure systems, which may explain the reliance of the big, non-biosecure pond farms of Latin America on SPR, rather than SPF shrimp.
- 12. • In any case, the use of SPF stocks is only one part of a complete plan for minimizing disease risks in shrimp culture. The development of SPF strains is really designed to help ensure that PL stocked into grow- out ponds are free of disease, one of, if not the most serious source of contamination. • Other areas of this strategy that must be implemented include: strategies to ensure broodstock, eggs, nauplius, larvae and juveniles derived from SPF stock remain SPF such as: • Farm biosecurity, early warning surveillance and rapid response to disease outbreaks.
- 13. SPR • Recent research work by some state and private companies has focused efforts on the development of SPF strains that are also resistant to specific pathogens (SPF/SPR). This is a long process, and usually focused on one pathogen at a time. Thus, although the development of pathogen resistant strains is a long- term goal of SPF breeding programmes, it is unlikely that they will ever result in strains that are unaffected by all disease organisms (Lotz, 1997). • SPR shrimp usually result from a specific breeding programme designed to increase resistance to a particular virus. • SPR strains of shrimp, however, do not necessarily have to be SPF
- 14. SPR Production • This is accomplished by challenging sub-lots of shrimp families to a particular pathogen (or combination of pathogens) and then selecting the most resistant families as broodstock for the next generation
- 15. • These strains are typically resistant to only one pathogen, currently largely either TSV or IHHNV, but some work has indicated that strains with multiple resistance to TSV and WSSV (at up to 25 percent survival to challenge tests) may be possible (Jim Wyban, per. com.). • SPR status for a particular pathogen is not lost due to management practices, although it can be lost in subsequent generations through poor animal- breeding and selection strategies.
- 16. Hawaii history SPR • A selective breeding programme for P. vannamei was initiated in 1995 in the Oceanic Institute in Hawaii. • Original work was based on a selection index equally for growth and TSV resistance (the major disease problem in the Americas at that time). • Confirmation that growth and survival (to TSV challenge) responded well to selection was obtained, but there appeared to be a negative genetic correlation between these traits. • However, selected shrimp (Growth and TSV resistant) were 5 percent smaller than control shrimp, revealing a negative genetic correlation between mean family growth and mean family survival to a TSV challenge.
- 17. • This negative correlation between growth and disease resistance must therefore be taken into account when developing breeding plans for these shrimp. Hawaii SPR • Using the Hawaii specific pathogen resistance (SPR) healthy P. Vannamei to increase the possibility of a more successful production. • This SPR Vannamei not only show negative for TSV,WSSV,BPV,IHHNV,YHV and HPV, but also get 81~88% high survival rate under the TSV attack, conducted by the University of Arizona and Oceanic Institute. • Like other animal, the virus-resistant ability of SPR healthy Vannamei may decrease after three to four generations. From time to time, it is needed to introduce new parent prawn to keep the virus-ability standard.
- 18. SPT • The vast majority of SPR being sold are SPT. • They are tolerant to the specific pathogen at a certain level of exposure to the particular pathogen. • SPT animals either do not develop the disease, or it has a lower impact than in normal animals, when they are infected with the specific pathogen for which tolerant status is conferred. • Tolerance is a quantitative characteristic. For example, there might be different degrees of tolerance to the pathogen. • If SPT animals have not been exposed to pathogens, they can also have SPF status, but being susceptible to infection, they cannot be SPR for that same pathogen. Unless these animals are also SPF, they are potential carriers of pathogens and therefore present a risk to spread diseases.