Vericore Ltd v Vetrepharm Ltd & Anor

This is the appeal of Vericore Ltd, the patentee of UK patent GB 2,270,261, from the decision dated 18 March 2002 of Mr Dennehey, Divisional Director, acting on behalf of the Comptroller, by which he held that patent to be invalid. The grounds on which he found for the respondents, Vetrapharm Ltd and Alpharma, were that claims 1 and 4 of the patent were not novel in the light of certain of the pleaded prior art and that, even had they been novel, all the claims were obvious. Although he expressed the preliminary view that there was unlikely to be anything inventive which could be salvaged from the patent, he gave Vericore permission to apply to amend. The issue of amendment has been stayed pending the outcome of this appeal.

This appeal is governed by paragraph 16 of the Patent Practice Direction pursuant to CPR Part of 52, rule 11 and CPR Part 49. It is therefore a rehearing but the appellate court will give great weight to the decision below. This is particularly true in relation to issues of fact which are dependent on, or significantly affected by, the evidence of witnesses and experts who have been cross-examined in the court or tribunal of first instance. In the present case, the hearing before Mr Dennehey lasted for three days and it included cross-examination of a number of those who had given written evidence. Mr Dennehey made findings as to the reliability of witnesses and the oral evidence given which have not been challenged. Indeed Mr David Young QC who, together with Mr Geoffrey Pritchard, appears here, as they had appeared before Mr Dennehey, on behalf of Vericore, says that he does not seek to challenge Mr Dennehey’s assessment of the witnesses nor does he seek to challenge his findings of “primary fact”. Furthermore, I understand Mr Young to advance no serious criticisms directed at Mr Dennehey’s recitation of the legal principles involved in this case. It is the application of those principles which is challenged on this appeal.

The patent is concerned with providing a solution to the problem of sea lice infestation which can be of particular concern were high densities of salmonid fish are to be found. The technical field of the patent is described as follows in the decision:-

“11.

Before turning to the subject matter of the patent, it may be helpful briefly to outline the technical field of these proceedings. It relates to salmon and other sea fish, and more especially to infestation with sea lice to which they are susceptible. Sea lice are ectoparasitic marine crustacea which eat the membrane, skin and blood of their host. There are two main types of louse relevant here: Lepeophtheirus salmonis and Caligulus elongates. Treatments for sea lice infestation do not differentiate between the two. On wild salmon only small numbers of sea lice are normally found, but in farming conditions where fish density is very high, infestation is a major problem. Heavy infestations cause stress amongst the fish, reduced feeding activity, and low weight gains. The consequences for the fish are highly unpleasant and may result in high mortality rates. Over the years, different treatments for sea lice infestation had been used, in particular the organophosphate dichlorvos. For various reasons which I shall come too, dichlorvos was not regarded as the last word, and alternative treatments were being sought.

12.

Pyrethrum is an extract from Chrysanthemum flowers which contains a mixture of natural compounds including pyrethrins. Pyrethrum powder has been used for many years as an insecticide in domestic situations. Compounds having similar structures and properties to pyrethrins have been developed as insecticides. The use of pyrethrum and related synthetic compounds in treating sea lice infestation on salmon and other seawater fish goes to the heart of the present dispute.”

The patent describes the relevant background to the invention in three paragraphs. First it says:-

“It is known commercially to treat salmon suffering from infestation with sea lice by the use of the insecticide dichlorvos. However dichlorvos is generally only effective against mature lice and is considered not to affect juvenile sea lice. Furthermore great care has to be taken with the dichlorvos dosage as the insecticide is fatal to fish at only 8 times the recommended dose for sea lice treatment. Further there are indications that resistance to dichlorvos is developing in sea lice. It is therefore desirable to find alternative agents for treating sea lice on salmon and other fish especially materials for which the dose recommended can be very much less than the fatal (LD₅₀) dose.”

There is nothing to suggest that any of this was not well known to those in the art at the priority date of the patent, namely 18 March 1991. In particular the toxicity of dichlorvos was well known and it was well known that it had to be administered at a concentration which was high enough to kill the lice but not so high as to kill the fish. As this paragraph points out, the safety margin for this insecticide was quite small. The patent then proceeds as follows:-

“It is known to use the pyrethroid pesticides cypermethrin and iTs related compound alphacypermethrin for both the control of pests in crops and against ectoparasites in cattle and sheep including scab, lice and ked in sheep (see The Pesticide Manual, 7th Edition, page 3690 ed CR Worthing, The British Crop Protection Council). Cypermethrin and alphacypermethrin are thus used in crop sprays or cattle and sheep dips or sprays. However they and other pyrethroids had not been proposed for use in treating fish. Although it is stated in the Pesticide Manual that the LD₅₀ (96 hours) for brown trout is 2.0 – 2.8 microgram per litre (mcg/l), such tests are only to check that fish are not at risk from normal agricultural usage. Further data on the toxicity of cypermethrin to fish is to be found in “Environmental Health Criteria 82: Cypermethrin”, published by World Health Organisation, Geneva in 1989 as part of IPCS International Programme on Chemical Safety. This summarises work on the toxicity of cypermethrin and reports in Table 8 that for technical cypermethrin, dispensed in ethanol, at 10^oC the LD₅₀ (96 hours) for an atlantic salmon having a weight of 5.3g is 2-2.4 microgram active ingredient/litre. Because of these figures it has been considered that cypermethrin is toO toxic for use on fish.

However, we have found that pyrethroids, particularly cypermethrin and alphacypermethrin, can be administered to salmon and other seawater fish in a manner which is highly effective in the control of sea lice in the salmon and other fish while being much less toxic to the fish themselves than dichlorvos.”

The nature of the invention is then described:-

“Accordingly, the invention provides the use of a pyrethroid pesticide, preferably cypermethrin or alphacypermethrin, for the manufacture of a composition for treatment of sea lice infestation in salmon or other sea fish in a seawater environment.”

The inventor does not claim to understand the factors which make the invention work. This is apparent from the following paragraph:-

“It is not fully understood why cypermethrin is not toxic to the salmon or other seawater fish in the circumstances in which it is used in this invention. This greater tolerance may be due to the presence of seawater rather than fresh water. The use of alphacypermethrin as a component of fish food for oral administration may also be an important factor. Certainly, it is particularly surprising that alphacypermethrin is highly effective when administered orally. Good results at dosage rates equivalent to 0.005mg/litre in water have been found whereas the dosage rate for dichlorvos to give equivalent results is of the order of 1mg/litre.”

The patent goes on to set out a number of examples which are said to illustrate the invention. I will have to consider these later in this judgment. Towards the end of the specification, the following passage is to be found:-

“A number of other pyrethroid pesticides have been tested in accordance with the invention and the following table gives the percentage mortality in sea lice following 1 hour bath treatments in-vitro with 6 different pyrethroid compounds each administered at 2 different concentrations.

	Hours past treatment
Compound	1	6
Negative control	0	0
Solvent (ABS) control	10	10
Cypermethrin 0.1 ppm	0	70
Cypermethrin 0.01 ppm	10	40
Deltamethrin 0.1 ppm	20	90
Deltamethrin 0.01 ppm	20	70
Resmethrin 0.6 ppm	50	70
Resmethrin 0.06 ppm	50	15
Permethrin 0.5 ppm	0	30
Permethrin 0.05 ppm	0	10
Cyhalothrin 0.2 ppm	60	40
Cyhalothrin 0.02 ppm	0	10
Tetramethrin 0.8 ppm	10	100
Tetramethrin 0.08 ppm	0	70”

There are 14 claims. Before Mr Dennehey no concession was made that any of these lacked independent validity. In the result, the validity of each was considered and found wanting. On this appeal Mr Young has only asserted independent validity for Claim 1 and claims 6, 8 and 9. He says that the latter 3 claims survive or fall together. The claims in contention read as follows:-

“1.

Use of a pyrethroid pesticide for the manufacture of a composition for the treatment of sea lice infestation in seawater fish in a seawater environment.

6.

Use of a pyrethroid pesticide in water for the manufacture of a treatment suspension for salmon suffering from sea lice infestation.

8.

Use according to claims 6 or 7 wherein the pyrethroid pesticide is administered in the range between 0.001 and 0.5 ppm by weight of pyrethroid pesticide to water.

9.

A composition when used for controlling sea lice infestation in salmon which comprises a pyrethroid pesticide suspended in water.”

I can now turn to the decision. As I have said, Mr Dennehey held all the claims to be invalid for obviousness over some of the pleaded prior art and claims 1 and 4 to be invalid for anticipation. The Applicants had advanced certain other attacks which failed. Mr Hacon, who appears, as he did below, for the respondent applicants, has not sought to advance any cross-appeal nor have his clients put in a respondents’ notice. They say that the conclusions and reasoning of Mr Dennehey were in all material respects correct.

Mr Dennehey has produced a model decision. His analysis of the facts and the law are clear and, save perhaps on one or two very minor factual points, unimpeachable. Indeed I have considered whether I should simply adopt the words used by Lord Diplock in Polaroid Corporation (Land’s) Patent [1981] FSR 578 and say that the decision below is obviously right and expressed in terms so clear and convincing that I do not think I can improve on them. However, out of deference to the arguments advanced by Mr Young, some of which may not have been put to Mr Dennehey, I shall consider below the major issues canvassed on behalf of Vericore and the reasons why I have come to the conclusion that Mr Dennehey’s decision is correct.

Two major arguments are put forward. The first is concerned with terminology. It will be seen that the patent and its claims refer throughout to “pyrethroids”. Two pieces of prior art, referred to throughout this appeal and by Mr Dennehey as D2 and D9, disclose the use of pyrethrum and its constituent pyrethrins to remove sea lice from salmon. Pyrethrum and the pyrethrins within it are natural products derived from chrysanthemum plants. Mr Young advances the argument that the proper technical meaning of the word “pyrethroid” refers only to a class of chemicals which are synthetic analogues of the natural pyrethrins. For this reason he says that the claims of the patent must be taken to be limited to the use of these synthetic compounds whereas D2 and D9 disclose the use of natural pyrethrins and pyrethrum only.

This issue is considered at paragraphs 61 to 71 of the decision. Mr Dennehey refers to the evidence given by the witnesses as to the meaning of the word “pyrethroid” in the art. He recounts that the word is used by most workers to encompass both synthetic and natural chemicals although there are undoubtedly some who use it in a more limited way as referring to the synthetics alone. Further, he makes reference to 7 technical documents dated 1990 or earlier, each of which, he says, uses the word “pyrethroid” in a way which clearly encompasses both natural and synthetic compounds. Some refer to pyrethrins as “natural pyrethrins”, “natural pyrethroids” or just treat them as part of the group of compounds known as “pyrethroids”. They use the expression “synthetic pyrethroid” to designate synthetic compounds. In fact in this section of the decision it appears that he has made an error. It is likely that one of the documents he relied on, namely “Veterinary Applied Pharmacology & Therapeutics” by Bander, Pugh and Bywater was provided to him, as it was to me, in an inadequately photocopied form. One part of a page was not visible. When a proper copy was produced during the appeal it became clear that the authors had written:-

“Like the natural pyrethrums, the pyrethroids are contact poisons which have a rapid paralytic action on insects, preceded by muscular excitation and convulsions.”

In this passage the term “pyrethroid” is used to refer only to synthetic compounds. Nevertheless, the documents taken as a whole support the evidence of the witnesses that most workers in the art use the term “pyrethroid” to cover both natural and synthetic compounds. As Mr Hacon points out, these documents show that amongst those who use the term in the wider sense is Dr M. Elliott who is regarded as one of the leading lights in the world of synthetic pyrethroids.

It follows that this word has a technical meaning which includes natural pyrethrins but that a minority of workers use it in a more restricted sense.

The next step is to consider how the term is used in the context of the patent. Mr Young argues that all the particular compounds referred to in the patent are synthetic, including all those in the table set out at paragraph 8 above. He says that the patentee must be taken to have intended to limit himself to synthetic chemicals. He says that there is no express reference to “synthetic” in the patent because there was no need to do so. It was implicit in the use of the word “pyrethroid”.

In my view Mr Dennehey was right to reject these arguments. The fact that all the pyrethroids mentioned in the patent happen to be synthetic does not indicate that the patentee intended to limit himself to synthetics. It leaves the matter unresolved. To the majority of readers, therefore, the use of the expression in the patent would have been taken to be a reference both to synthetic and natural compounds. If the patentee had intended to use the term in the less usual restrictive sense, he should have done so explicitly.

There is an additional reason why, in my view, Mr Dennehey’s decision is correct. As Mr Young accepts, there is nothing in the patent to suggest that the inventor thought, or had reason to suspect, that natural compounds would not work in the same way and just as well as synthetics. The passage in the specification set out at paragraph 8 above shows that the inventor did not know what the mechanism was which made his treatment works. The only suggestion that he makes is that the tolerance is due to the presence of seawater rather than freshwater. Nowhere in the evidence is it suggested that any reader would consider that, if this is the underlying reason for the success of the treatment, it would not apply just as readily to the use of natural pyrethrins. In other words there is nothing in the patent to suggest that the patentee believed that his treatment worked because the compounds he used were synthetic rather than natural. There is therefore nothing to suggest that the inventor intended to limit himself to synthetics. His invention would be thought to cover the synthetic and natural compounds.

One other major point is advanced by Mr Young in response to the attack of anticipation. He argues that although both D2 and D9 teach the use of pyrethrum to selectively kill sea lice on salmon, they do not anticipate because they do not describe anything which is sufficiently effective to fall within the meaning of the word “treatment” as used in the claims. Mr Hacon says that the reason why Mr Dennehey does not deal with this in his decision is that it was not argued before him.

Mr Young says that in the context of the patent “treatment” must mean effective to kill at least somewhere in the region of 95% of the sea lice. If so, neither of these pieces of prior art anticipate since they disclose kill rates of 74% and 89%.

In my view there is nothing in this point. The patent includes no suggestion that any particular level of efficacy is required. Furthermore it appears that there is only one example in the patent of anything which reaches or exceeds the level suggested by Mr Young, namely the use of tetramethrin at 8 ppm as recorded in the table set out at paragraph 7 above. All the others fall short, and in some cases far short, of the 95% level. Mr Young’s response is to say that none of these examples are within the claims. I find this a difficult argument to accept. Not only does the patent not indicate that the examples are outside the scope of the invention claimed, but all of the examples which involve use of pyrethroids do so at dosage levels well within the ranges selected as particularly inventive in the claims.

Mr Hacon is right when he argues that the procedure which removes, say, 74% of the sea lice parasite is a “treatment” of sea lice infestation and falls within the claim. Consistent with this is the view expressed by one of the expert witnesses, Professor Stenersen, that the experiments in D2 and D9 exhibited “remarkable success”. The fact that all the witnesses appear to have accepted that, at least by 2002, the sea lice kill levels described in these pieces of prior art were not sufficiently high to be commercially acceptable does not mean that they are outside the scope of the claims.

For these reasons, the appeal against the finding of anticipation fails.

Although Mr Dennehey found obviousness over three pieces of prior art, namely D1, D2 and D9, it is sufficient to consider the first of these. This document is the DSc thesis of a Dr Horsberg and his wife, Dr Tonje Høy. It refers to D2 and D9 which are publications produced by a team working at the Institute of Marine Research in Norway. Mr Young says that if D1 is a prior publication, it can and should be read together with D2 and D9. The contents of these three documents are considered fully in the decision under appeal. For present purposes it is convenient to set out their major disclosures. I shall deal with them chronologically.

D2 – “New Pesticide for Salmon Lice – promising trial using pyrethrum”

This document is a published summary of a presentation given by Mr Jens Holm and Mr Per Jakobsen on 16 January 1990 as part of the 1990 Annual Meeting Seminar on Fish Health in Norway. As its title indicates, it reports what it claims are promising results obtained by using pyrethrum to kill salmon lice. It starts with a short description of existing treatment of these parasites and notes that radically new methods of treatment have not been found. It then says “We believe we have found the answer”. That is the use of natural pyrethrum. It is claimed that this substance is more effective and far preferable to current synthetic nerve toxins (which would include dichlorvos). On page 2 the following is said:

“PYRETHRUM, a neuroactive mixture of pyretrins, is an effective pesticide. Introductory tests at the Marine Aquaculture Station Austevoll have shown that this substance can be toxic to fish if emusified (finely distributed in water). However, this problem has been averted and the fish can now be deloused without the risk of dying because the salmon louse has a lipid layer in its outer shell, while the salmon’s slimy outer layer is water soluble. By allowing the salmon to hop through a layer of oil containing the fat soluble pyrethrum, we found that we could get pyrethrum into the salmon louse in effective concentrations, while leaving the fish unaffected. We added an anti-oxidant (piperonyl-butoxide) to retard the photo-chemical destruction of the pyrethrum. …

In the following, we present the results of one of several tests carried out at the Marine Aquaculture Station Austevoll in the autumn of 1989, which in our opinion demonstrates pyrethrum’s potential. The treatment method described here is probably not optimal. A number of optimisation tests will hopefully be carried out at the Marine Aquaculture Station Austevoll in 1990.”

A test is then described which is said to demonstrate a significant effect of the pyrethrum on the sea lice. The authors describe pyrethrum as a very promising candidate as a pesticide for salmon lice and say that further tests will be carried out. They also praise the use of pyrethrum, not only because it is a natural product, but because it is environmentally friendly since it can be derived from plants grown in non-agricultural land in a developing country, Kenya, to the benefit of poor farmers there. It also states that

“… parasites present in Norwegian salmon fish farming can be eradicated with a natural substance extracted from flowers …” (emphasis added)

D9 – “Alternative Chemical Treatments to Sea Lice”

This is the published text of a presentation at the Irish Salmon Grower’s Association Annual Conference and Trade Exhibition given by the same Messrs Holm and Jakobsen together with Ms K. Blixen. The first page is an abstract. It contains a brief description of the problems caused by sea lice infestation in the sea pens used in salmon farming and then goes on to describe pyrethrum. The authors state that using this for treating fish “did not cause mortality in the salmon”. They then go on to say as follows:-

“The first administration principle is to surround the cage with a plastic canvas collar, and add the pyrethrum mixture to the water surface within the cage. The salmon leaping activity will provide self-delousing with a minimum of stress. The leaping activity is higher in infested compared to non-infested fish, and is decreasing with size. However, the method have some negatives at present. Degradation of the pyrethrum (by light), as well as the removal of oil after the treatment are topics for further project activity. This method will be a effective for small fish when light intensity is medium or low. The other principle is to submerge the fish in a small reservoir of pyrethrum mixture. This seems to be more reliable and controlled, but will induce more stress. The method can be combined with grading or change of nets.”

Pages 2 to 10 containing a more detailed description of the use of pyrethrum to combat sea lice infestation. On page 2, the authors state as follows:-

“... Pyrethrum is readily broken down by sunlight into harmless metabolites so for outdoor use an antioxidant is needed.

In 1987 the testing of new delousing agent was started at Austevoll Aquaculture Research Station. One of the first experiments used a Pyrethrum emulsion. Then we rediscovered that emulsified in water Pyrethrum is poisonous to fish and acts very much like Rotenone (used in watercourses to remove fish populations). In the autumn of 1989 a new administration principle was used for the first time. This method make use of the fact that Pyrethrum is oil soluble. Pyrethrum and antioxidant were mixed with an oil and poured on top of the fish cage. The oil solution was prevented to float away by a plastic collar. The idea was to let the salmon jump through the layer and delouse themselves. A significant treatment effect was observed. The high water content of the salmon mucus leaves the fish unharmed. The salmon lice however has a lipid membrane in the exoskeleton that makes oil solubles able to selectively penetrate the lice and not the fish.”

The authors go on to describe the two application methods alluded to in the abstract, namely the use of an oily surface layer containing the active ingredients and the “dipping” or “bath” method. Lice mortality rates of 88% are said to have been achieved with the first method and 89% with the latter. The Conclusion on page 10 includes the following:-

“Pyrethrum has shown itself to the effective as a delousing agent but the method of applying the Pyrethrum is not optimal at the moment.

So far the best achieved result is a total delousing of 89%. This was in the bath experiment. The issue must be to find a way to apply the right amount of Pyrethrum in the easiest way for the farmer.”

D1 – “Chemotherapy of Sea Lice Infestations in Salmonids: Pharmacological, Toxicological and Thereapeutic Properties of Established and Potent Agents”

This thesis considers the nature of sea lice infestation and its impact on fish farming, the existing treatment and its defects and a number of potential alternative treatments. Five of the latter are mentioned. The last of these is introduced as follows:-

“5.2.5

Pyrethroids

Among the substances currently being studied for their potential as delousing agents in salmon are the pyrethroid insecticides. In Norway, interest has so far been concentrated on pyrethrum, an extract of the plant Chrysantehmum cinerariaefolium containing various pyrethrins with insecticidal properties. Preliminary clinical trials with pyrethrum administered on the water surface using an oil as the vehicle, have demonstrated a certain chemical effect on sea lice (Jakobsen & Holm, 1990).

Pyrethrum is, however, a mixture of insecticidal agents which are extremely toxic to fish. The LC₅₀ (96 h) of a 20% pyrethrum extract is 24.6g/l for rainbow trout (Mauk & al., 1976). Being highly toxic does not necessarily exclude a substance from therapeutic use, since it is the margin between the toxic dose for the parasite and the toxic dose for the fish that is important. This margin remains, however, to be determined for pyrethrum. The extremely high toxicity towards several non-target aquatic organisms also raises the question of possible adverse impact of any solution released into the environment.”

Having referred to the fact that pyrethrins are light and oxygen sensitive and therefore must be used with additional anti-oxidants, the authors continue:-

“Due to the instability of the natural pyrethrins and the need for the addition of several chemicals to overcome this, synthetic derivatives are used as insecticidal agents. These include compounds such as deltamethrin, permethrin, cypermethrin and fenvalerate, and more recent products such as flucythrinate, fluvalinate etc. The synthetic pyrethroids are more stable than the pyrethrins, and are equally or more potent pesticides. It seems probable that in the future, synthetic pyrethroids will be of more interest than pyrethrum as possible delousing agents.”

Against the background of this prior art, I can now consider the major arguments advanced by Mr Young. The first issue is whether D1 was published before the priority date of 18 March 1991. This is dealt with by Mr Dennehey at paragraphs 51 to 56 of the decision. The major point taken by Mr Young is that Dr Horsberg only distributed copies of his thesis to other people within his department prior to that date and that such disclosure should be treated as internal. Mr Young argues that had anyone from the department taken a copy of the thesis to a competitor on, say, 17 March 1991, it would have been considered a breach of duty to the department or to him.

This submission takes no account of the unchallenged evidence of Dr Horsberg that as soon as the thesis was returned from the printers on 27 February 1991, it was the intention to make it available to the public at large from that date and was treated as such. Amongst other things, this resulted in copies being sent to libraries before the priority date, although they were not proved to have actually been put on the public shelves by the receiving library before that date. No doubt a few days were taken for transit in the post and for the libraries to catalogue the thesis prior to public display. However on the facts of this case, the intention was to make the thesis available to the public as soon as reasonably possible after its return in final form from the printers. Consistent with this, Dr Horsberg gave the following evidence relating to how his thesis was treated in Norway:-

“On 27 February 1991, I also supplied copies of the thesis to people who requested a copy of it. Consequently, various employees of the NVH, including my supervisor and other scientific and technical personnel, received copies of the thesis from me at that time. No expressed or implied restrictions were placed by me on the use of the thesis by the recipients of it. No copyright was declared in the thesis. The recipients would have been free to use the thesis however they saw fit. Likewise I would not consider as confidential, copies of theses I received from colleagues and students. The nature of a doctoral thesis is that it is a public document, intended for publication.”

Copies of the thesis was sent to the Study Section of the Norwegian School of Veterinary Science on or before 4 March 1991. Dr Horsberg explained:-

“The Study Section is open to the public during office hours and to my knowledge, once the thesis was delivered to the Study Section, anyone could have seen it.”

Such limited oral evidence as was given in relation to this subject supports the view that the thesis was available for inspection by anyone before the priority date. It is therefore prior art.

The next major argument is that Mr Dennehey was in error in assessing who was the relevant addressee of the prior art for the purpose of an obviousness attack. Mr Young says that the addressee is a fish health expert alone. Although he accepts that Mr Dennehey’s precis of the law, including case law which confirms that the addressee may have the technical expertise of a team of workers from different disciplines, he says that Mr Dennehey was wrong in this case to conclude that the notional addressee had relevant expertise of both a fish health expert and a toxicologist. One of the reasons this plays a major part in Mr Young’s argument is that it is the precursor to an argument that the fish health expert would be put off use of pyrethrum and pyrethroids because of their known toxicity to salmon. Whereas a toxicologist might not be deterred, a fish health expert would, so he argues. In particular the latter would not realise that a dosage “window” might exist at which these agents would be too dilute to kill the fish but at high enough concentration to kill the lice.

In fact there is nothing in this latter argument because, not only was the existence of just such a window known for the existing treatment using dichlorvos, but D1 expressly identifies the existence of this in the passage concerning the “margin” of toxicity.

In any event, the argument relating to the characteristics of the addressee of the prior art also fails. Each of these documents propose the administration of poisons. In my view Mr Dennehey was correct to say that the relevant addressee would have both fish health expertise and toxicology expertise. In real life it would be a team. This can be looked at in two ways. D1 suggests that synthetic pyrethroids are probably the way forward. If this were read by a toxicologist, say someone in the employee of a company making such compounds, he would call in a fish health specialist consider the application of this class of compounds to fish. On the other hand, if the prior art were read by a fish health expert who was ignorant of pyrethroids toxicology, he would inevitably call in someone with that expertise. In either event one ends up with an addressee having both areas of expertise.

Mr Young also argues that the results set out in D1, D2 and D9 together are insufficiently good to justify further experimentation. This dovetails into his argument, referred to above, that the prior art produces results which are not sufficiently good to qualify as “treatments” of sea lice. I have already considered that. This more general argument also fails. The skilled worker reading this art, and particularly the passages set out above, would realise that the use of synthetics was highlighted as a probable way forward, that the initial tests were extremely encouraging and that further optimisation would be necessary. Professor Stenersen’s reaction referred to in paragraph 22 above is understandable and would be the reaction of the notional addressee. There is no reason to believe that such an addressee would reject the steer given by Dr Horsberg. The fact that there were other promising routes does not diminish the obviousness of trying this one.

Finally I must deal with claims 6, 8 and 9. As mentioned above, before Mr Dennehey, Vericore did not limit the number of claims for which it maintained independent validity. On the other hand it does not appear that it paid particular attention to any of them other than claim 1. Before me, Mr Young maintains that there is something special and inventive about using a suspension as the means of delivering the pesticide. Mr Hacon protests that this was never asserted in the evidence, argued before Mr Dennehey or foreshadowed in Mr Young’s skeleton argument. Even if these criticisms are correct, one must not lose sight of the fact that the onus of proving obviousness is on the respondents.

Mr Dennehey found that suspending pesticide in water was a standard way of using them. Mr Young does not challenge this. On the other hand he points to the fact that in prior art documents D2 and D9 an emulsion of pyrethrum was said to be toxic to fish, at least at the dosage levels there used. He argues that if an emulsion was toxic, a non-inventive skilled addressee would expect a suspension to be so. He puts forward an explanation for the relative toxicity of pyrethrum as follows. He says that one of the two methods of administration suggested in D2 involves the use of a pyrethrum-containing oil layer floating on the seawater. Salmon irritated by lice infestation jump more than non-affected salmon. They therefore jump through the oil layer. During this passage the lice and outer skin of the salmon are brought into contact with the pyrethrum but the inside of the gills are not. The salmon therefore do not absorb the pyrethrum through their gills. If an emulsion or suspension we used, the salmon would breathe the pyrethrum-containing seawater, would absorb the pyrethrum and would die.

There are a number of problems with this. I only need referred to two of them. First, the suggestion that the survival of the salmon can be attributed to lack of access by the pyrethrum to the inside of the gills is not supported or suggested by any of the evidence in the case. Second, it ignores the fact that the bath or dipping process described in the prior art, which gives the best results, cannot be explained on this basis. It seems to me that this argument is linked to Mr Young’s attempt to exclude toxicologist expertise from the notional addressee of the prior art. Once one embarks upon attempting to use synthetic pyrethroids as suggested in the prior art with the assistance of a toxicologist, it would have been obvious to at least try using the pesticide in a standard and simple way, namely as a suspension. There is nothing in this case which suggests that warnings about using pyrethrum in an emulsion at the levels indicated in the prior art would have deterred a toxicologist from trying a pyrethroid in suspension at the probably lower dosage levels he would choose. It should also be borne in mind that D9 ends with the suggestion that there should be investigation of easier methods of administration. In so doing, the document states the obvious. It follows that this response to the obviousness attack also fails.

For these reasons I will dismiss this appeal.