WO2005089536A1

WO2005089536A1 - Cage suitable for housing laboratory animals in isolation and related ventilation system

Info

Publication number: WO2005089536A1
Application number: PCT/IB2005/000701
Authority: WO
Inventors: Pietro Bernardini; Alfredo Campiotti
Original assignee: Tecniplast S.P.A.
Priority date: 2004-03-19
Filing date: 2005-03-18
Publication date: 2005-09-29
Also published as: ITMI20040530A1; DE212005000018U1; CN2927678Y

Abstract

The cage for laboratory animals according to the invention comprises: - an inlet valve (1) and an outlet valve (2) respectively capable of allowing air to enter into and exit from the cage; - an external casing (4) capable of separating, essentially sealed against leakages of air, the environment (3) inside the casing itself, and which is downstream from the inlet valve and upstream from the one outlet valve, form the environment outside it. The exiting air is purified by means of a filtration system (7,7A) capable of containing the majority of the infective agents, and placed upstream from the outlet valve. The external casing is composed of two half-shells (4,8;4,9) between which an airtight seal with U section is interposed. The invention also relates to the ventilation system to ventilate the cage; such system is equipped with a ventilator unit solely sucking or solely blowing.

Description

CAGE SUITABLE FOR HOUSING LABORATORY ANIMALS IN ISOLATION AND RELATED VENTILATION SYSTEM Field of the invention

The present invention relates to a cage for the housing of laboratory animals in isolation from the external environment, and the system for ventilating it. Prior art

At the present time, for the study of infective agents with laboratory animals in structures with safety level BSL3 (Bio Safety Level 3, that is structures for working with infective agents that can cause serious or deadly diseases by means of inhalation, such as the recent SARS and the West Nile viruses) "isolators" are used, which are essentially airtight containers isolated from the external environment, usually kept at a slight pneumatic under-pressure in relation to the outside, and within which infected laboratory animals are placed; the laboratory operator may handle the animals in the isolator by means of sleeves and flexible gloves attached to the isolator and these are also hermetically sealed against possible escapes of air and infective agents from the inside. For experiments on laboratory animals at lower danger levels, however, various types of IVC, Individually Ventilated Cage, are widely used: such cages, compared to the isolators, have various and significant ergonomic advantages; up to now, however, no individually ventilated cages exist capable of separating the external environment from the one inside them with a safety level of BSL3 or comparable. The aim of the present invention is to indicate an individually ventilated cage for laboratory animals and a cage ventilation system with improved features of sealing, containment of infective agents and isolation from the external environment compared to known individually ventilated cages and related housing systems.

Summary of the invention

This aim is achieved, according to a first aspect of the present invention, with a cage suitable for housing laboratory animals, said cage comprising: - at least one inlet valve capable of allowing air to enter into said circuit inside the cage; - at least one outlet valve capable of allowing air to exit from the inside of the cage towards an environment outside it;

- an external casing, capable of separating, essentially sealed against leakages of air, the environment inside the casing itself and which is found downstream from the at least one inlet valve and upstream from the at least one outlet valve, from the environment outside it, and/or capable of containing any infective agents inside said internal environment downstream from the at least one inlet valve and upstream from the at least one outlet valve.

In a second aspect of the present invention, this aim is achieved with a cage ventilation system for laboratory animals, said system comprising: - a plurality of housings for cages, each one capable of hosting at least one cage capable in turn of housing one or more laboratory animals;

- an air distribution circuit capable of drawing air from the environment, distributing it to the cages inserted, as the case may be, in said housings for cages and evacuating it from said cages. This system is characterised in that it also comprises a pneumatic head generator unit capable either of solely sucking the air through said distribution circuit from upstream to downstream, or solely pumping it through said distribution circuit from upstream to downstream.

The advantages attainable with the present invention shall become more evident, to the technician skilled in the art, from the following detailed description of an example, which is not restrictive, of a specific embodiment, with reference to the following figures.

List of figures

Figure 1 schematically shows a side view of an example of an embodiment of an individually ventilated cage according to a first aspect of the present invention;

Figure 2 schematically shows a cutaway side view of the cage of Figure 1 ;

Figure 3 schematically shows a perspective view of the lid of the cage of Figure 1;

Figure 4 schematically shows the view of a cross-section of the airtight seal along the joining edge of the two half-shells of the cage in Figure 1 ; Figure 4A schematically shows a detail of a cross-section of the joining edges, closed together, of the cage of Figure 1 , with the seal of Figure 4 deformed;

Figure 5 schematically shows a detail of a section along a vertical plane of the locking zone of the cage of Figure 1;

Figure 6 schematically shows a perspective view of the connecting element of the locks and related locking/unlocking system of the cage of Figure 1 ; Figure 7 schematically shows a cutaway view of the outlet valve of the cage of Figure 1 ;

Figure 8 schematically shows a cutaway view, along a vertical plane, of the indicator device for the internal under-pressure/over-pressure of the cage of Figure

1;

Figure 9 shows a scheme of a preferred example of embodiment of the ventilation circuit for cages for laboratory animals according to a second aspect of the present invention;

Figures 10 and 11 schematically show two cutaway views, along a longitudinal section plane, and in closed and open configuration respectively, of a port used in the ventilation system of Figure 9 to supply and evacuate air from a cage of Figure 1 ;

Figure 12 shows a variant of the cage of fig. 1 that highlights slide supports of the cage and slide rails, and an enlargement of it;

Figures 13A and 13B show a further variant of the cage of fig. 1 with regard to the fastening systems; Figures 14A and 14B show details of the fastening systems of figures 13A and

13B, along the cross section T-T, relating to the fastening clasps in closed and open positions respectively.

Detailed description of the invention

Figures 1-8 relate to a non limiting preferred embodiment of an individually ventilated cage, indicated with the overall reference 100, according to a first aspect of the present invention. Such cage is equipped with an inlet valve 1

(Figures 1-3) capable of allowing the entry into the cage of air coming for example from an air distribution circuit, and with an outlet valve 2 capable of allowing the exit of air from the inside of the cage towards a suitable downstream branch of the air distribution circuit. Valves 1 and 2 are preferably integrated within the lid 8 of the cage.

The cage defines inside it a space 3 (Figure 2) where one or more laboratory animals may be housed, for example mice, rats or guinea pigs. According to a first aspect of the present invention, the cage also comprises an external casing 4 (Figure 2) capable of separating, essentially airtightly, the environment inside the casing itself situated downstream from the inlet valve 1 and upstream from the outlet valve 2, or in any case, capable of containing potential infective agents inside the casing, such as for example bacteria or viruses; the casing 4, in the present example in the form of a plastic shell, encloses and isolates from the environment outside the cage both all laboratory animals infected or "pure", as the case may be, and all the objects or parts inside the cage, and the substances potentially and usually infected by the animals - or remainders of food or excrements - and that need to be handled by the operator during the cleaning and ordinary maintenance of the cages: in this way a laboratory operator in order to come into contact with these infected objects and materials is obliged to open the cage, which avoids or, in any case, significantly reduces the probability of contamination of the operators themselves.

Preferably the cage is equipped, inside the casing 4, with a drinking dispenser 5, a supporting grate 6 made of steel wire or sheet metal or plastic material, and with a filter 7 capable of containing at least the majority of the pathogenic agents potentially in suspension in the air exiting from the casing. Such a filter can be for example a HEPA filter (High Efficiency Particulate Air Filter) or other class 4 or 5 absolute filter in accordance with ISO 14644.1 , or a class M2.5 or M3.5 HEPA filter in accordance with Federal Standard 209E: such filters indicatively allow from 2300 to 23000 particles of granulometry not greater than 0.2 μm per cubic meter of filtered air to pass through, and are therefore capable of containing within the cage the majority of the currently known kinds of infective agents, present, as the case may be, within the cage.

Preferably the filter 7 equipped with an airtight O-ring is placed in the proximity of and upstream from the outlet valve 2, and is preceded by a precleaner made of tissue-non-tissue 7A. Both the filter 7 and the precleaner 7A are removable and may be replaceable.

In the present example of embodiment, the external shell 4 consists of two half- shells 8, 9 made of suitable plastic material and which may be joined along their respective joining edges, in order to close the cage (Figure 2). Along the whole of the joining edge of the upper half-shell 8, also called in the present description lid 8, advantageously runs a closing seal 12 (Figures 4, 5) with cross sections with essentially thin walls and in the form of a U. With the expression "cross-section with thin walls" in the present description is meant cross-sections with walls of thickness essentially not greater than one third of the maximum transversal size of the section itself; in the present example of preferred embodiment, the closing seal 12 is made of silicone rubber with a ratio (thickness of the thin walls)/(maximum size of the U section) ranging between circa 3.5-4.

Seals with cross-sections with thin walls may be made of elastomeric materials - such as silicone rubber - not expanded, capable therefore of withstanding the pressures typical of autoclave disinfection treatments, and are capable of ensuring good sealing against leakages of air with closing pressures that can be withstood by the other parts of the cage.

The U seal of the present example of embodiment is also equipped with four ribs 13, 14 essentially triangular in shape and that run continuously along the whole length of the seal; each of the ribs 13 is placed at the end of the two branches of the U, whereas the ribs 14 are placed at the bottom of the U section. The housings on the two half-shells that house the seal 12 are shaped in such a way as to squeeze it, during the closure of the cage, on the four ribs 13, 14 - in a vertical direction, with reference to Figure 4 - so that it warps slightly at the sides (Figure 4A) in order to produce also on the sides contact zones against the side walls of the housings and sealing. This seal is therefore capable of ensuring overall a better seal against leakages of air, in comparison to other known seals.

To ensure a more efficient seal and distribute the closing pressure more uniformly along all the joining edges, the cage of the present example of preferred embodiment, essentially rectangular in shape, is equipped with at least two fastening zones 15 (Figure 1) on each of the long sides of the cage; this is especially more advantageous the larger the size of the cages. Each fastening zone 15 comprises a hook 16 (Figure 5) and a link rod 17 that fixes the hook 16 to the lid 8 and can be locked in closed position and unlocked springing between two stable positions.

Preferably but not necessarily the two hooks 16 of the two fastening zones 15 on the same side of the cage are attached to - or in any case connected by - a single connecting element 18 (Figure 1 , 5) that allows them to be hooked and unhooked at the same time, with a faster movement and reducing the probability of forgetting to fasten one of the many fasteners otherwise present in greater numbers. In addition, preferably each of the two connecting elements 18 can be locked in fastened position or unlocked by means of a suitable safety lock. In the present example of embodiment, the safety lock comprises the button 19 and the peg with T section 20 (Figure 1 , 5). The T peg 20 is integral with the lid 8, whereas the button 19 is mounted on the connecting element 18 and can slide up and down in relation to it; when the two fastening zones 15 are hooked, the safety button 19 can be pressed so that a suitable female seat present on it inserts itself above and attaches itself to the peg 20, in order to stop the opening of the two fasteners 15, whereas in order to open the cage it is first necessary to lift the button 19. This prevents involuntary or accidental openings of the cage, for example in the case of a fall or banging against an obstacle. On the other hand, in the variants of figures 13A and 13B the fastening zones 15' are separate.

Preferably fastener 15 is equipped with a pair of ribs 141 (figures 14A, 14B) that create a friction with the link rod 17. The friction between the fastener 15 and the link rod 17 allows the fasteners 15 to be held apart during the positioning and removal of the half-shell 8 on/from the half-shell 9. This spreading apart prevents undesirable interferences.

Preferably on the internal side of each connecting element 18 one or more noise reduction buffers 21 (outlined with dashes Figure 1) made of soft material- for example rubber or elastomer - that reduce the noise of the connecting elements 18 that when closing bang against the lid 8, in order not to irritate the animals held inside the cage.

Figure 7 schematically shows a cut away of the valve 2 for the passage of air to and from the cage, according to the present example of preferred embodiment (in the present example the inlet valve 1 is made in a essentially identical manner): the valve 2, in the present example suitable to be connected to a circuit for the introduction and evacuation of air described in more detail below, comprises a mobile element 200 - specifically a slider 200 - made of suitably rigid plastic material - as will be explained in more detailed below - and indicatively tubular in shape, and two ring seals 201 , 202 - for example two O-rings in rubber or elastomeric material as in Figure 7: the O-ring 201 , located on the outside of the casing 4, avoids or, in any case, significantly reduces the leakages of air between the slider 200 and the seat 203 - within which the slider runs - when the valve 2 is open and displaced completely to the right as it is connected to the air distribution circuit - described in more detail below - whereas the O-ring 202, located inside the casing 4, avoids or in any case significantly reduces leakages of air between the slider 200 and the seat 203 when the valve 2 is closed and displaced completely to the left - pushed by a return spring, not represented - as it is disconnected from the air distribution circuit. In Figure 7, the arrows schematically show the path of the air through the valve.

In this way the valve 2 achieves a double seal against leakages, both when open and when closed. When the slider 200 is in an intermediate position, because the valve is opening or closing, the leakages between slider 200 and seat 203 towards the outside of the cage are in any case avoided by the under-pressure - or by the over-pressure - in relation to the ambient pressure found within the cage.

In other forms of embodiment, not represented, the function of the slider 200 may be carried out more in general by a mobile, for example rotating or pivoting, element and the pair of O-rings may be replaced for example with a single element in elastomeric material that achieves a double sealing.

Figure 8 schematically shows a display device for the internal pressure/underpressure, indicated by overall reference 300, with which a cage according to the present invention can be advantageously equipped. Such display device comprises an indicator membrane 301, for example in silicone rubber, capable of deforming itself or in any case moving according to the difference in the pressures that are in the chamber 302 - that is inside the casing 4, since the chamber 302 is in pneumatic communication with the compartment

304 downstream of the filter 7 and upstream of the outlet valve 2 - and outside of the casing 4 - that is in the zone 303 of the compartment 302.

An indicator pin 305 is integrally fixed on the indicator membrane 301 that, depending on the deformations of the membrane, enters or exits the cylindrical seat 306. The tip of the pin 305 is preferably coloured so that it is clearly visible when it in protrudes outside.

By observing the tip of the pin 305 an operator can immediately realize, thanks to a very simple and reliable device, if inside the cage according to the invention there is the expected working under-pressure or over-pressure, or if there are abnormal conditions - for example the internal pressure of the cage is equal to the ambient pressure and there is therefore the risk of escapes of infective agents from the cage - and take suitable precautions.

Advantageously the discoidal support 307 that contains all the other components of the display device is attached to the outside wall of the casing 4 through a pair of O-rings 308, 309 that, in addition to ensuring an adequate seal against escapes of air from inside, achieve a "floating connection" that enables the compensation of the distortions that may arise when the cage undergoes autoclave treatments.

For further safety the display device for pressure/under-pressure 300 is placed downstream of the filter 7 and upstream of the outlet valve 2, in an uncontaminated zone as it is downstream of the HEPA filter 7.

Figures 9, 10 relate to the system of housing and ventilation for laboratory animals in cages for example of the type described above.

Such housing, in the present example of embodiment, comprises a shelved supporting frame defining a plurality of housings, each of which can house a cage

100 (or more cages 100, as the case may be).

Each cage 100 can be for example positioned with the slide supports 121 (Figures

1 and 12) on the horizontal slide rails 22 of the housing system. As can be seen better in the enlargement of Figure 12, the slide supports 121 are equipped with raisers 122, preferably slanted, at their ends that, with the cage inserted in the housing system, secure themselves to the corresponding end raisers 221 of the rails 22, locking the cage in place. To insert the cage 100 into the housing system, the supports 121 slide on the slide rails 22, all the way down, where the elasticity of the unions 603 is taken advantage of, as they attach themselves elastically to the valves 1 and 2 (fig. 3), and therefore the raisers 122 secure themselves definitively to the corresponding raisers 221. To remove the cage 100 from the housing system, the cage is pushed towards the unions 603, the front end of the cage is raised, so that the front raisers 122 lift up in relation to the corresponding raisers 221 , and the cage is removed, unbinding the unions 603 from the valves 1 and 2. The profiles of the rails and supports allow the immobilisation of the cage 100 by exploiting the elasticity of the unions 603 without the use of additional kinetic motions.

The support frame also supports a series of piping 600-602, 614 (Figure 9) that is used to bring and extract ventilation air to/from each cage 100 inserted in one of the housings of the shelf.

The air sucked from the external environment through a main pipe 600 is distributed to a plurality of secondary pipes 601, pneumatically connected in parallel to the main pipe 600, and from each secondary pipe 601 to the cages 100 inserted in their housings, through a pair of connection unions 603 (Figures 9, 10): a first port 603 is connected to the inlet valve 1 of a cage 100 to introduce new air into it, and a second port 603 is connected to the outlet valve 2 of the same cage 100 allowing the evacuation of the old air.

The rounded tip 604 of the unions 603 binds itself to the corresponding concave surface 204 (Figure 7) of the valves 1 and 2 of the cages. Preferably both the tip 604 of the unions 603 and the concave surface 204 are portions of spherical surfaces, the second with radius greater than the first: this coupling of shapes allows the obtainment of greater sealing against leakages from the coupling valve/port by compensating for the dimensional imprecisions of the parts of the coupling. The Applicant has verified that greater sealing is obtained by making the tip 604 of the unions 603 and the concave seat 204 using essentially rigid plastic material rather than soft or rubbery, and the possible leakages through the coupling are in any case eliminated by the difference in pressure already mentioned -in overpressure or in under-pressure - between the inside of the ventilation circuit and the external environment. The old air exiting from the cages through the secondary outlet pipes 614 (Figure 9) reaches the main outlet pipe 602 and is then evacuated.

In a second aspect of the present invention, the distribution circuit of ventilation air to and from the cages 100 is connected to a pneumatic head generator 605 - for example a ventilation pump or a ventilator - capable of functioning a) only sucking air from the cages 100 if these are placed upstream of the head generator 605 in the pneumatic circuit, or b) only pumping air towards the cages 100 if these are placed downstream of the head generator 605 in the pneumatic circuit, without blowing air into the cages from upstream and simultaneously sucking air from a position pneumatically downstream of the cages as happens in the air ventilation and distribution systems currently known. This brings the following advantage: if some cages 100 were to be ventilated with a combined system of pumping from upstream and simultaneous sucking from downstream, in the event of breakdown of the downstream suction pump in the cages 100 an over-pressure in relation to the external environment would inevitably be established, because the upstream pump would continue to blow air; therefore a housing system for example with safety level BSL3, that should function with the cages 100 permanently in under-pressure in relation to the outside, would work instead in over-pressure, with high risk of infective agents escaping from the cages towards the outside. Instead, with a ventilation system according to the present invention the head generator unit 605 in the event of breakdown can at worst cease to function, but cannot invert the pressure differential between the inside and the outside of the cages 100. The continuity of functioning can in any case be ensured by a reserve pump, this also only blowing or only sucking. A symmetrical circumstance occurs in the case of a ventilation system of a known type that has to function with the cages 100 at pressure higher than the ambient pressure in the event of breakdown of the upstream pump, and also in this case a ventilation system according to the second aspect of the present invention is advantageous.

The head generator unit 605 is pneumatically connected to a control cage in which the difference in pressure between the inside and the outside of the cage is recorded. This difference in pressure enables the self-regulation of the head generator 605 to guaranty in each cage the maintenance of said parameter within the set thresholds. The control cage may be equipped with a system displaying the functioning and safety parameters.

The head generator unit 605 is equipped with an uninterruptible supply unit and has two motors. In the case of breakdown of one of the two motors, the maintenance of the sign (positive or negative) of the pressure differential between the inside and the outside of the cage is nevertheless guaranteed. Preferably the ventilation system comprises at least one upstream filter 607 (Figure 9) to filter the air that is sucked from the external environment before introducing it into the cages, and at least one downstream filter 608, downstream from the cages 100 and outside them, to filter the air coming from the cages before expelling it from the ventilation system, further reducing the risks of contamination; preferably the upstream filter 607 and/or the downstream one 608 are also HEPA filters. In the case that an upstream HEPA filter is present, the unions 603 that allow air into the cages can be non airtight, since the risks of contamination are eliminated by the presence of the HEPA filter.

Advantageously, in the case of a ventilation system with cages 100 in pneumatic under-pressure in relation to the outside, at least the unions 603 that supply the air to the cages are of the type of Figure 10, namely they behave like a valve that opens when they are connected to a cage 100, whereas they close when they are not connected to any cage: in this way the undesirable situation shown in Figure 11 is avoided: in the ventilation system of Figure 11 the delivery openings do not have the valves 603 and if, as in the Figure, a cage 100 is not inserted in some of the housings, from the entry openings non filtered air is sucked directly from the environment with consequent pollution of the air correctly filtered by the upstream filter 607 located at the suction of the entire system. In the port 603 of Figure 10 the closure of the valve is achieved thanks to the elastic force of the bellows 605 that, in the absence of cage 100 to be supplied, push upwards the shutter 604 so that the conical head 606 closes the valve. When a valve 1 or 2 pushes against the rounded end 604 of the port 603, the latter opens letting the air pass through the hole 609. In the present example of preferred embodiment the shelved supporting frame with its air distribution piping is mobile on wheels and also mounted on it is the unit with the blowing or sucking ventilators, so that it can roll on the floor and be freely moved from one place to another maintaining a plurality of cages 100 always connected to a pneumatic pressure or under-pressure generator circuit. It should be noted how the ventilation system and the cages for the housing of the animals previously described combine the advantageous aspects - especially the convenience and speed of use - typical of individually ventilated cage systems with the features of confinement of infective or in any case noxious agents, and in general of safety, characterising isolation structures such as the known isolators. The Applicant has verified that the cage and the cage ventilation system described above are able to ensure a degree of confinement of BSL3, or comparable, of infective agents and noxious substances between the outside and the inside of the cage that is isolated or inserted in its ventilation system. The cages and the ventilation system described above are open to numerous modifications and variations without nevertheless going beyond the scope of the present invention.

For example, the ventilation system described above can also be used with known types of cages suitable for the housing of laboratory animals or in any case different from the cages according to the first aspect of the present invention. Each modification and variation that falls within the meaning and the range of equivalence of the claims is considered as being comprised within them.

Claims

1) Cage suitable for housing laboratory animals, said cage comprising: - at least one inlet valve capable of allowing air to enter inside the cage; - at least one outlet valve capable of allowing air to exit from inside the cage towards the environment outside it; - an external casing, capable of separating, essentially sealed against leakages of air, the environment inside the casing itself and which is located downstream from the at least one inlet valve and upstream from the at least one outlet valve, from the environment outside the casing itself, and/or capable of containing any infective agents inside said internal environment downstream from the at least one inlet valve and upstream from the at least one outlet valve.

2) Cage according to claim 1 , comprising a filter enclosed inside said external casing and capable of filtering the air coming from the zone inside said casing suitable for housing the laboratory animals before it exits from the external casing through the at least one outlet valve, said filter being placed essentially upstream from the outlet valve.

3) Cage according to claim 2, wherein said filter is capable of containing the majority of the infective agents potentially in suspension in the air present inside the casing.

4) Cage according to claims 2 or 3, wherein said filter is preceded by a tissue- non-tissue precleaner.

5) Cage according to claim 4, wherein said filter 7 and said precleaner are removable and replaceable. 6) Cage according to one of claims from 2 to 5, wherein said filter is of the type HEPA, or other class 4 or 5 absolute filter according to ISO 14644.1 , or of the HEPA type of class M2.5 or M3.5 according to Federal Standard 209E. 7) Cage according to claim 1 , comprising at least two half-shells that comprise an upper half-shell and a lower half-shell, capable of being fastened along their respective joining edges in order to close under seal said external casing, and at least one closing seal placed along the joining edge of at least one of the half-shells, wherein said closing seal has cross sections with essentially thin walls. 8) Cage according to claim 7, wherein said inlet and outlet valves are both within said upper half-shell. 9) Cage according to claim 7, wherein said at least one closing seal has essentially U cross-sections. 10) Cage according to claim 9, wherein said at least one closing seal comprises at least one rib that runs longitudinally to the seal itself and is placed so that it rests against the joining edge of one of the half-shells. 11) Cage according to claim 7, wherein the perimeter of the joining edges of the half-shells defines one or more sides and the cage comprises a closing system capable of closing the half-shells by pressing them one against the other and comprising on at least one of the said sides two fastening zones in which the two shells can be reversibly fastened to each other. 12) Cage according to claim 11, wherein on at least one side of the perimeter of the joining edges at least one of the two half-shells comprises a connecting element that connects at least two of said fastening zones in order to be able to simultaneously connect and unconnect them to the other half-shell. 13) Cage according to claim 11, wherein each one of said fastening zones comprises one clasp and one link rod that fastens said clasp on said upper half-shell and can be locked in closed position and unlocked springing between two stable positions. 14) Cage according to claim 3, wherein said clasp is equipped with ribs that cause friction with said link rod, said friction permitting said clasp to be held apart_during the positioning or the removal of the upper half-shell on/from the5 lower half-shell. 15) Cage according to claim 12, wherein said connecting element can be locked in closed position or unlocked by means of a safety lock. 16) Cage according to claim 11, wherein the said two fastening zones are separate.

D 17) Cage according to claim 12, comprising at least one locking/unlocking system capable of locking or unlocking the at least one connecting element. 18) Cage according to claim 1 , comprising indicator means for the internal under- pressure /over-pressure capable of indicating whether the pressure inside the casing is higher or lower than the pressure outside the casing. 19) Cage according to claim 18, wherein the indicator means for the internal under-pressure /over-pressure comprises: - an indicator membrane, of which at least one part is capable of deforming itself or moving depending on whether the difference between the pressure inside said external casing is higher, equal or lower than the pressure outside the casing itself, and - indicator means capable of rendering the position and deformation of the indicator membrane visible from the outside of the casing. 20) Cage according to claim 1, wherein at least one amongst the at least one inlet valve and the at least one outlet valve comprises: - a mobile element capable of moving between an open position, in which the valve can allow the air to flow from inside the casing to outside or vice versa, and a closed position, in which the valve separates, sealed against leakages of air, the inside of the casing from the environment outside it; - a seat for the mobile element, in which the mobile element can move to go from the open position to the closed one; - means of double sealing, capable of preventing or limiting the leakages of air between the mobile element and its seat, both when the valve is in open position and when in it is in closed position. 21) Cage according to claim 20, wherein the means of double sealing comprises at least: one double seal, two seals, at least one body made of rubber or elastomer. 22) Ventilation system for said cages for laboratory animals according to any of the preceding claims, said system comprising: - a plurality of housings for cages each suitable for housing at least one cage suitable in turn for housing one or more laboratory animals; - an air distribution circuit capable of drawing air from the environment, ) distributing it to the cages inserted, as the case may be, in said housings for cages, and evacuating it from such cages, also comprising a pneumatic head generator unit capable of either solely sucking the air through said distribution circuit from upstream to downstream or solely pumping it through said distribution circuit from upstream to downstream.

23) Ventilation system according to claim 22, wherein said air distribution circuit comprises a line of air distribution capable of delivering air to at least two cages for the housing of laboratory animals pneumatically in parallel to each other, said line being equipped with a plurality of unions each capable of opening and letting through air supplying one cage when this is inserted in the housing for cages where the valve is found, and capable of closing itself blocking the passage of air when there is no cage inserted in the housing where the valve is found.

24) Ventilation system according to claim 23, wherein said plurality of unions are equipped with a rounded tip that attaches itself to a corresponding concave surface of said valves.

25) Ventilation system according to claim 24, wherein said rounded tip and said concave surface are portions of spherical surfaces, the second with radius greater than the first.

26) Ventilation system according to claim 24, wherein said rounded tip and said concave surface are in essentially rigid plastic material.

27) Ventilation system according to claim 22, wherein said cage comprises horizontal slide supports and said housing comprises horizontal slide rails, said cage being positioned with said slide supports on said horizontal slide rails, said slide supports being equipped with raisers at the ends that, with a cage inserted into the housing system, secure themselves against the corresponding end raisers of said rails, immobilising the cage. 28) Ventilation system according to claim 27, wherein said unions are elastic, contributing to the insertion and removal of the cage from said housing.

29) Ventilation system according to claim 22, further comprising at least one upstream filter to filter the air that is sucked from the external environment before introducing it into the cages, and at least one downstream filter, downstream of said cages and outside them, to filter the air coming from the cages before expelling it from the ventilation system.

30) Ventilation system according to claim 29, wherein said upstream filter and/or said downstream filter are HEPA filters.

31) Ventilation system according to claim 23, wherein said head generator unit is pneumatically connected to a control cage in which the difference between the pressure inside and outside the cage is recorded, said control cage being equipped with a system to display the functioning and safety parameters.

32) Ventilation system according to claim 23, wherein said head generator unit is equipped with an uninterruptible supply and has two motors, in case of breakdown of one of the two motors, the maintenance of the sign (positive or negative) of the pressure differential between the inside and the outside of the cage being guaranteed.

33) Ventilation system according to claim 23, wherein the closure of at least one of said unions is controlled by an elastic element.

34) Ventilation system according to any one of claims from 22 to 33, comprising at least one cage according to any one of claims from 1 to 21 connected to said air distribution circuit.