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CONVENTIONAL AND SPECIFIC PATHOGEN FREE ANIMALS  (SPF ANIMALS)

The term “conventional” is used to describe animals that are reared with a minimum barrier system and that may carry organisms pathogenic for their own or other species.

Disease control in populations of such animals may be achieved by the use of appropriate vaccines or chemotherapy. Individual animals showing signs of disease should be isolated and treated or killed.
 Conventional animals that may harbor zoonotic agents, they should be caged, managed and handled in such a way as to minimize any risk of infection being transmitted.

Specific pathogen free animals) are animals that are free from specified microorganisms and parasites but not necessarily free from other non-specified microorganisms. Such animals are normally obtained though hysterectomy (cesarean or direct removal of the animals from the fetus) and maintained in controlled sterile environment .such animals are sometimes referred to as clean animals, disease free animals, pathogen free animals or microbiologically defined animals

 SPF animals are therefore disease free animals that have been sought for many years by sourcing them from stocks that had been originally established from hysterectomy. These animals, after heterectomy, are taken and maintained within a barrier called specific pathogen free building (SPF building).

This building is specifically designed to barriers separating the animals from possible sources of infections. Inside this building, animals are maintained in a diet, nesting and bedding materials that are sterile and are usually cared by a skilled technical staff.

Personnel in such units are required to adopt hygiene standards and wear clothing that prevents them carrying infection to the animals in their care. Access of personnel to such units should be limited in order to minimize the possibility of introducing infection.

The objective in managing microbiologically defined animals is to ensure that their microbiological status remains the same throughout their lifetime.

The key to this development is the aseptic removal of fully developed fetus, which have always been protected from the external pathogens by placenta, from the mother by heterectomy.   The fetus is then aseptically introduced and maintenance in a sterile environment.

Heterectomy must be done in a suitable room that is outside the SPF building and the operator and their assistant must be in dressed in protective clothing. The heterectomized animal should be shaved on its ventral surface before she is humanely killed. The animal is then pinned on a sterile dissecting board and its abdomen is covered with an adhesive sterile tape.

Surgery is done aseptically to remove the fetus and the fetus should be protected from the unitarily outside surface of the mother. Either it’s important to stress here that these process should be absolutely aseptically and any form of contamination through the instruments used or the protective clothing’s etc. should be minimized.

Care should be taken so as not to puncture any part of the mother or the fetus. This is because these may allow entry of pathogens into the fetus. The fetus should be taken while still intact and protected by the uterus and should be immediately introduced, while inside a covered box containing a long acting disinfectant, into an isolator or in the SPF building    

Nevertheless, some pathogens might gain entry into the fetus through the placenta, which may cause this aseptically obtained animal, not really disease free. Its therefore necessary that heterectomized or caesarian derived young animals be quarantined in a germ free isolator until when    rigorous tests will be conducted to show that they are   absolutely pathogen free.

This is when they  are allowed into an SPF building .Animals free from specified pathogenic organisms require to be maintained in  SPF buildings in which filtered air and treated food and water are supplied using utensils that are adequately disinfected.

Inside the isolator or the SPF building, the uterus is opened using a sharp sterilized scissors to remove the fetus. The conditions in the isolator should be optimal for the fetus e.g.  Temperature, humidity and pressure should be favorable. The young animals should be fed daily on sterile food directly or by fostering to a lactating mother already inside the isolator or SPF built.