To calculate the potential for blood transfusion transmission it is first necessary to note that there is approximately a 70% chance that a TSE can be transmitted from one species to any other specific species (Dealler, 1993) and so it must be assumed that there is an underlying 30% chance that humans can never become infected with BSE. One then has to estimate the number of people that would be expected to receive adequate oral doses from their food for infection to take place (TSE infectivity in lymphoid tissues and blood is found early in the incubation period of the disease (Dealler, 1993)). It is then assumed that, as most BSE infected tissue that might have been eaten by humans during the BSE epidemic has already been consumed (Fraser & Foster, 1993), human peripheral blood donations might contain the agent in 1995. By using various possible scenarios for the amount of infectivity needed to infect a human by mouth, and the relative amount of infectivity present in the bovine tissue, it is possible to calculate the number of otherwise unexposed individuals that would receive blood transfusions from a human who was previously infected with BSE.
The number of cases of BSE in cattle in the UK and their individual ages of onset are published annually by the Ministry of Agriculture Fisheries and Food (MAFF). The case population is large enough that, using official data for the age distribution of all the cattle in the UK, it is possible, using standard techniques, to calculate the number of infected cattle that would have been eaten before showing clinical signs of BSE. It is also possible to calculate the point in their incubation period at which they were slaughtered (Dealler, 1993). Using relatively accurate data for the level of TSE infectivity found in the liver, kidney, muscle, and peripheral nerves of other species, and using information concerning the relative changes in levels of infectivity that take place during the incubation period, it is possible to estimate the infectious load that people in the UK may have eaten by 1995 (method fully published; Dealler, 1993, Dealler and Kent 1995, Dealler, 1996).
Unfortunately it is not known how much BSE infectivity is needed to infect a human by mouth and we must assume a 70% chance that this is possible at all (Dealler, 1993). In mice 104 IU of scrapie (from another mouse) appears to be orally infective (Kimberlin & Walker, 1989), but few data such as this are available. As such it is necessary to calculate the number of people that might become infected if various possible infective doses for humans are considered (Table 1). The lowest of these, 103 IU is probably unrealistically low, just as the highest, 109 IU, which may well represent the infectivity present in 10g of bovine brain from a cow dying of BSE, is unrealistically high. From Table 1 it is clear that nobody could have become infected if bovine tissues carry a low level of infectivity and 108 IU are needed to infect human by mouth. However, everyone might potentially be at risk if bovine tissue is highly infective and if only 105 IU are required. Currently we have no way to decide which of the scenarios, if any, of Table 1 is the most likely to be correct.
Clearly someone already infected by BSE will not be further infected by transfusion. Also, someone who will die of other causes will not be affected by an infection that may have an incubation period of 20 years. The proportion of total adults (and hence potential donors) that would be infected with BSE is taken from Table 1). Each of the figures in Table 1 gives rise to a separate figure for the people that would become infected from blood transfusion but would not otherwise catch BSE and these are shown in Table 2.
Scrapie, the TSE of sheep, has been found in the bloodstream of animals affected with the disease; in mice (Field, 1967; Clarke & Haig, 1967, Field et al., 1968); in rats (Clarke & Haig, 1967), in hamsters (Casaccia et al., 1989), in sheep (Gibbs et al., 1985). CJD has been found in the blood of infected mice (Kuroda et al., 1983), guinea pigs (Manuelidis et al., 1978) and humans (Manuelidis et al., 1978; Tateishi et al., 1980; Tateishi, 1985; Manuelidis et al., 1985) and with persistent viraemia demonstrated in the buffy coat (Manuelidis et al., 1978). No infection was found, however in the blood of scrapie infected goats (Hadlow et al., 1974), similarly infected mice (Dickinson et al., 1969; Eklund et al., 1967) and CJD or kuru sufferers when the disease was inoculated into mice (Gibbs & Gadjusek, 1972; Gajdusek, 1977).
Mink inoculated with blood from a mink suffering from transmissible mink encephalopathy showed no sign of disease (Marsh et al., 1973) nor was scrapie in the goat transmitted by peripheral inoculation into a separate goat (Pattison & Millson, 1979). These findings suggest that viraemia is present at such low levels as to sometimes prevent disease transfer across a 'species barrier' or when inoculated in small amounts (Casaccia et al., 1989).
The dose of infectivity that has been shown to be infective by i.v. transmission in mice is only 9 IU (Kimberlin & Wilesmith, 1994) and the amount of infectivity expected to be present in 300 ml of human blood would, if similar to that found in the hamster, be greater than 104 IU throughout the incubation period (Casaccia et al., 1989). However, the peripheral transfusion of 300ml of whole blood from a patient suffering from CJD to a chimpanzee has not led to disease after 8 years (Gajdusek, 1990) but the 'species barrier' and the long incubation period that is expected may rule this out as a helpful indicator.
It is suspected that, as CJD derived from pituitary hormone inocula may lead to a spongiform encephalopathy similar to kuru, so might that derived from blood transfusion (Esmonde et al., 1993), but few cases (about 5%) are of this clinical form. Of 202 patients identified as having CJD, 16 had a definite history of blood transfusion and this was found to be similar to a matched control group (Esmonde et al., 1993). The sporadic CJD symptoms were also found to be similar to those in individuals who had received a blood transfusion. This would suggest that blood transfusion is currently an unlikely cause of CJD. The model calculated used here agrees with this; with fewer than 25 cases of CJD annually (as there have been prior to 1990) less than 2 people would be expected to have received infected blood by transfusion and to have survived 20 years (data not shown). This inoculation would, however, have taken place 20 years ago and CJD incidence data from this period is poorly available. Four Australians died of CJD (with symptoms similar to kuru) 5 years after receiving a blood transfusion (Klein & Dumble, 1993) but inadequate statistical data are available to demonstrate a relationship with transfusion.
The report of a man dying of CJD who had donated blood between 1971 and 1991 show both that 18 recipients had died - none from CJD, that one had reached 22 years without signs of CJD, and 9 were still alive, the oldest being 21 years and healthy (Heye, 1994). These findings, although they are the only ones published, may suggest that intravenous transmission of CJD through blood may indeed need a very long incubation period or not take place at all. The possibility that CJD is present only in the cellular fraction may mean that non-cellular recipients are not at any risk, but further research is required.
The general population and the medical profession of the UK are mindful of the risks of CJD transmission by transfusion (Contreras & Barbara, 1991; Watkins, 1991; Arya, 1991; Contreras et al., 1991). If indeed there does prove to be a risk of BSE being transmitted to humans via the food chain, then the potential opportunity for secondary transmission by transfusion of blood and its components would appear to be far outweighed by the potential of transmission via food.
Dose of Relative infectivity of dietary beef tisue for BSE infective BSE compared to other species infected with a to humans (IU) TSE*** Low Medium High 10E3 33.74* 33.76 33.76 (33.37-33.76)** (33.76-33.76) (33.76-33.76) 10E4 30.77 33.37 33.76 (22.58-32.53) (32.76-33.76) (33.76-33.76) 10E5 0.46 20.28 33.76 (0.13-1.09) (18.38-22.12) (31.5-33.76) 10E6 0 17.32 32.56 (17.32-17.35) (23.16-32.64) 10E7 0 0.133 17.42 (0.036-0.137) (17.35-17.66) 10E8 0 0 17.34 (8.82-17.34) 10E9 0 0 0.036 (0.036-0.13) *Figures relate only to people aged 16 to 64 yrs (34.6 million) in the UK as data are not adequately available for younger or older age groups. Figures represent the numbers of UK people that would have eaten a specific cumulative infective dose (Y axis) by 1999 given the infectivity of bovine tissue as related to other species with a TSE (X axis). Calculated using MAFF data at December 1993 and published methods (Dealler, 1993). If the infective dose is not cumulative then these figures should be calculated in a separate manner (Dealler and Kent, 1995); this is, however felt unlikely. These calculations assume that only 10% of peripheral nerve reaches the human diet and that no 'specified offals' (brain, spleen, thymus, gut etc), which were banned from the human diet in November 1989, were ever eaten. They assume that all clinically infected catlle are reported to MAFF, that all diagnoses are accepted by their veterinary officers, that all are correctly diagnosed by histology and that no cattle born after 1991 ever develops BSE. ** Upper and lower limits of 95% confidence interval. *** Using known levels of infectivity found in the tissues of other species infected with TSEs as references.
Original oral Relative infectivity of dietary beef tissue dose of BSE compared to other species infected with a TSE postulated to have infected the blood donor (IU)
Low Medium High 10E3 0* 0 0 10E4 14.1 0 0 (5.6-48.0)**
10E5 4.3 54.7 0 (1.2-10) (49.5-58.9) (0-10.6) 10E6 0 60.6 5.6 (60.6-60.7) (5.4-46) 10E7 0 1.3 60.5 (0.3-1.3) (60.5-60.6) 10E8 0 0 60.6 (54.8-60.6) 10E9 0 0 0.3 (0.3-1.3) *Figures relate to UK transfusion recipients (thousands) in 1995 under 51 yrs of age who would otherwise not be at risk of BSE but who would have received blood from UK donors shown in Table 1 (i.e. donors that would have eaten a specific (cumulative) infective dose of BSE (Y axis) by 1999 and with consideration of the relative infectivity of bovine tissue as compared with other species with a TSE (X axis)). Calculations: ((Blood units used - wastage)/2.1) x (proportion of donors infected by 1995) x (proportion of recipients not infected orally by 1999) x (proportion under 50 yrs) x 0.5 (half the number of transfusions in which 2 potentially infective units were used). This is statisitcally organised to give an indication of the number of people that would receive a transfusion of 1 unit of blood from a person infected with BSE by 1995 and would themselves be expected to live another 20 years. ** Upper and lower limits of 95% confidence interval. Transfusion Medicine 1996;6:213-5 Editorial. Blackwell Scientific
This edition of Transfusion Medicine contains an article by Dr. Dealler outlining his personal assessment of the potential risk of BSE to humans posed by blood transfusion in the UK (Dealler, 1996). This is particularly timely given the recent report from the CJD Surveillance Unit in Edinburgh of 10 cases of a new variant form of CJD and a possible aetiological linkage with BSE (Will et al, 1996).
CJD is a rare disease with an incidence of approximately one per million population (Collinge and Rosser, 1996). The majority of cases occur sporadically, some are inherited - so called familial CJD - and others have been attributed to the transfer of infectious material (Brown et al., 1992).
These latter cases are largely related to the administratio of pituitary-derived hormones. Pituitary-derived growth hormone and pituitary derived gonadotrophins used in the management of infertility have both been associated with subsequent development of CJD. The disease has also been transmitted from implantation of dura mater and following corneal transplants. Acquired, or iatrogenic, CJD is one of particular relevance to Transfusion Services since it demonstrates that the disease can be transmitted by therapeutic agents, and that transmission can occur via peripheral routes as well as by direct intracerebral inoculation. Inevitably this raises the question of the possibility that CJD and other forms of prion disease might be transmitted by transfusion of blood or blood products.
The biology of these diseases has recently been reviewed (Prusiner, 1995). Scientific opinion favours the 'prion hypothesis' whereby the disease is caused by the presence of an abnormal form of a naturally occurring protein. The existence of 'proteinacious infectious particles' (prions) as a causative agent of spongiform encephalopathies was first postulated by Prusiner (in fact by Bolton - Ed) and subsequent work has demonstrated that these infections can be transmitted in the absence of nucleic acid, thus differentiating them from viruses. Prions are remarkably resistant to normal virus inactivation procedures. In prion disease the natural protein PrP protein) is converted into an abnormal form (termed PrPsc).
The prion appears to be capable of converting normal PrP which has a multiple helical structure into the abnormal variant where much of the back bone structure straightens out, thus setting up a cascade and building up of the abnormal form. The abnormal PrP may arise by random change in a normal individual, as occurs in sporadic CJD. In familial CJD a point mutation in the DNA coding for the protein leads to an increased susceptibility to formation of the abnormal form. These observations are of relevance to transfusion. If the prion is presenting the blood of asymptomatic individuals harbouring the disease then the protein could be transmitted by transfusion and this could occur in sporadic and familial forms as well as in iatrogenic disease. Thus in theoretical terms the underlying aetiology may be less relevant in the context of the ability to transmit the disease by transfusion. This will be important when considering possible mechanisms for minimising the risk of transmission of CJD by this route.
Transmission of prion disease between different animals can occur. This appears to be limited by a 'species barrier'. different forms of prion protein presumably differ i their capacity to transform normal human PrP into the abnormal prion form. This issue is discussed by Dealler in his article when considering whether BSE poses a risk to humans.
The possibility that the newly described variant of CJD might represent a human form of BSE raises two issues for transfusion. Firstly, once BSE has been able to produce disease in man the species barrier would not be of relevance in the context of onward transmission by transfusion. Secondly, the transmission characteristics of variant CJD may differ significantly from those of the classical form of the disease. In this particular setting the absence of documented transmission of CJD by transfusion cannot be taken as evidence that the new disease cannot be transmitted by this route.
Two main sources of evidence exist which may enable us to determine the likelihood that prion disease might be transmitted by blood. This involves data arising from studies in the experimental mouse model and second information from epidemiological studies.
Experimental data has demonstrated that the prion agent is present in buffy coat cells of infected animals (Manuelidis et al, 1985). This involved direct intracerebral inoculation of infected cells. Peripheral inoculation , i.e. into the blood stream, has not been associated with development of disease in animal studies (Brown, 1995). No data on the risk of transfusion of plasma appears to be available. these data should be viewed with caution and the results may not necessarily pertain to the potential risk of transmission of CJD, or indeed BSE, by transfusion to man.
A number of published studies have reviewed the epidemiological characteristics of reported cases to determine whether transfusion may be a possible source of prion disease in man. Esmonde et al (1993) reviewed 202 cases of CJD reported to the CJD surveillance unit in Edinburgh. there was no excess of cases with a history of blood transfusion or indeed donation of blood. It was concluded that blood transfusion is not a significant risk factor for CJD (in numbers as small as these Ed). Klein and Dumble (1993) reported four cases of CJD that had occurred in Australian recipients of blood transfusion and highlighted the need to establish effective surveillance of this particular disease to enable an accurate assessment of risk to be undertaken. Heye et al (1994) reported a look back study of recipients of an individual donor who had subsequently developed CJD. Recipients of 35 out of 55 donations could be identified, of whom nine were alive at the time of study. No evidence of transmission of CJD was found. There has been no reported case of CJD in multiply exposed haemophiliacs despite many years of treatment with fractionated coagulation concentrates. Operalski and Mosley (1995) cite such evidence as indicating that such products do not pose a risk for prion transmission. Creange et al 1996) however, describe a case of CJD arising in a recipient of a liver transplant who received human albumin solution; one of the donors contributing to the pool was subsequently diagnosed as having probable CJD.
In summary, the experimental evidence, although limited, identifies a theoretical risk that prion disease might be transmitted by transfusion. There is, however no clear evidence that this has occurred. The paucity of data is of concern and it is important that steps are now taken to establish effective surveillance of reported cases of CJD, particularly so in the light of the reported possible linkage of BSE to the newly described variant of CJD within the UK. The absence of evidence of transmission does not equate to an absence of risk, particularly so in a low-incidence disease such as CJD.
Transfusion Services have a responsibility to take reasonable steps to prevent inadvertent transmission of infections. In the absence of diagnostic assays suitable for use in the transfusion setting the only effective mechanism currently available to minimise the risk is by exclusion of individuals considered to be at higher risk of acquiring the disease. Transfusion Services in the US and Europe exclude potential donors who have received treatment with human-derived growth hormone. Within the UK, human growth hormone recipients have been excluded since 1989 and recipients of pituitary-derived gonadotrophin since 1993. Exclusion of recipients of dura mater and corneal transplants is undertaken in some countries as is exclusion of donors with a family history of CJD. The potential impact of this latter exclusion should not be underestimated. In contrast to recipients of pituitary-derived hormones, such individuals with not have received counselling in relation to any increased risk and this particular exclusion will need to be very sensitively handled to avoid unnecessary concern being caused. Inevitably the introduction of donor exclusion criteria in this area will result in established donors being identified who are deemed to be 'at risk'. This will result n notifications to plasma fractionators. Different views on the requirement for action have been taken by regulatory authorities in Europe and the USA. Interim guidance from the FDA in the USA requires plasma pools which contain donations from implicated donors to be quarantined, and fractionated product must only be issued for therapeutic use if withholding them would result in an inability to meet clinical needs (FDA, 1995). Within Europe there is currently no requirement to take such action. These different approaches are perhaps symptomatic of the paucity of reliable scientific data relating to transfusion and prion disease. The inconsistent approaches will present problems to manufacturers of fractionated plasma products and will need to be addressed. Most importantly, we must take urgent steps to overcome this lack of information to enable future decisions to be evidence based. In particular, we require evidence that CJD, especially the putative bovine passaged variant, does not transmit to experimental animals by the intravenous route, regardless of dose. Naturally, these types of investigations would be greatly helped if a convenient test for the rapid diagnosis of CJD could be developed.
Study Host Inoculated Assay Route Transmission/ Animal material animal inoc total number inoculated Scrapie (natural) Hadlow et al (1980) G Clot/serum M ic 0/3 Hadlow et al (1982) S Clot/serum M ic 0/18 Scrapie (experimental) Pattison and Millson G whole blood G ic 0/14 (1962) Gibbs et al (1965) S serum M ic 1/1 Clarke and Haig (1967) R serum R ic 1/1 M serum M ic 0/39 Eklund et al (1967) M whole blood M ic 3/13 Dickinson and Meikle M whole blood M ic 0/3 (1969) Hadlow (1974) G clot M ic 0/20 Diringer (1984) H blood H ic 5/5 Casaccia et al (1989) H blood H ic 10/11 CJD (experimental) Manuelidis (1978) Gp buffy coat Gp all 10/28 Kuroda (1983) M buffy coat M ip 4/7 G=goat, S=sheep, M=mouse, H=hamster, R=rat, Gp=Guinea pig ic=intracerebral, ip=intraperitoneal NB some of the samples inoculated were pools.There were always problems with this sort of experiment. The reason being that only small amounts of contamination of the inoculum with infective material would be enough to give effectively false positive results and, because such small amounts were inoculated (in mice this might only be 20 microlitres for instance) the level of sensitivity of the tests might be low. Pattison and Millson had a problem in that they were ordered to slaughter their goats when quite young (around 4 years) and as such, if low levels of infectivity were present, the animal mgiht not have lived long enough to develop disease. Experiments in which the inoculum crossed a species barrier (e.g. Hadlow, 1980/82) and then were inoculated into a small animal must have meant that the tests were poorly sensitive.
Study Donor Inoc Assay Route Transmissions/ diagnosis material animal total inoculated specimens Manuelidis sporadic buffy G'pig ic 2/2 et al (1985) CJD coat Hamster Tateishi sporadic whole Mouse ic 1/3 (1985) CJD blood Tamai et al sporadic concent Mouse ic 1/1 (1992) CJD plasma Brown et al sporadic whole Chimp iv 0/3 (1994) CJD blood sporadic whole Spider ic,iv,ip 0/1 CJD blood monkey sporadic whole Squirrel ic,ip,im 0/1 CJD blood monkey sporadic buffy Squirrel ic,iv 0/4 CJD coat monkey sporadic whole Guinea ic,ip 0/1 CJD blood pig kuru serum Mouse ic 0/3 Deslys et al hGH whole Hamster ic 1/1 (1994) CJD bloodBrown then spends a section of his paper describing why the results of the other researchers might have not been valid. One of his arguments was against Manuelidis in that they also found the blood of normal people were infective when looking for Alzheimer's disease and that the result was a spongiform encephalopathy in 26/30 tests. The worry with this sort of disease has always been with contamination and Brown suggested that for this own results (although I am only told this by his peers) when he found infectivity in the ash of incinerated scrapie tissue. However, the disease produced is fatal and untreatable so the researchers are able to identify it in the animals inoculated. Brown goes on to say that yes, we should assume human blood to contain infection but whether there is enough to pass the illness to another person by transfusion is not clear.
These sort of experiments are exteremely difficult and it is plainly difficult to interpret a negative result as indicating that there is no infectivity present. The reason for this is simply because the size of the inoculum is very low (in mice often 20 microlitres), a species barrier is present, usually of unknown size and only a small number of animals can be tested for purely economic reasons (i.e. a million people may be inoculated with blood from BSE infected people but only 5 blood samples have been tested in mice). A good example of how the results cannot be thought of as sensitive is the paper by Tateishi (1985) in which he tests blood products by inoculation into mice. The results may be as good as can be dont but are very difficult to indicate that there is no infectivity present.
Deslys JP, Lasmezas C, Dormont D. (1994) Selection of specific strains n iatrogenic CJD. Lancet 343:848-9
Diringer H. (1984) Sustained viraemia in experimental hamster scrapie. Arch. virol 82:105-9. Gibbs CJ, Gajdusek DC, Asher DM, Alpers MP, Beck E, Daniel PM, Matthews WB (1969) CJD (spongiform encephalopathy): Transmission to the chimpanzee. Science 161;388-9.
Gibbs CJ, Gajdusek DC,Morris JA (1965). Viral characteristics of the scrapie agent in mice. In Slow, Latent and Temperate virus Infections NINB monograph no 2. PHS Publication no 1378. Edited by Gjdusek DC, Gibbs CJ, Alpers M, Washington DC, . US Government Printing Office. p195-202.
Hadlow WJ, Kennedy RC, Race RE, Eklund CM. (1980) Virologic and neurohistologic findings in dairy goats affected with natural scrapie. Veterinary Pathology 17:187-99.
Hadlow WJ, Kennedy RC, Race RE. (1982) Natural infection of Suffolk sheep with scrapie virus. J Inf Dis. 146:657-64.
Kondo K, Kuoiwa Y. (1982) A case control study of CJD association with physical injuries. Ann. Neurol. 11:377-81
Little BW, Allentown PA, Mastiranni J, Philadelphia PA, DeHaven AL, Dover DE, Brown P, Goldfarb L, Gajdusek DC. (1993) The epidemiology of CJD in Eastern Pensylvania. Neurology A316:614P
Manuelidis EE, de Figueiredo, Kim JH, Fritch WW, Manuelidis L. (1988) Transmission studies from blood of Alzheimer disease petients and healthy relatives Proc. Natl. Acad. Sci. USA. 85:4898-4901.
Tamai Y, Kojuma H, Kitajima R, et al, (1992) Demonstration of the transmissibe agent in tissue from a pregnant woman with CJD. N. Engl J. Med. 327:649
Tateishi J, Tsuji S. (1985) Unconventional pathogens causing spongiform encephalopathies absent in blood products. J Med Virol 16:11.
Human pharmaceuticals made from human blood products. There does not seem to have been much discussion about the use of human products and nv-CJD being passed on. Recently one or two of the recipients seem to have realised that this may not be very clever as one in 200 of the blood donors may actually be incubating BSE at this time according the recent Nature article.
MAFF now asking for blood samples They are being asked to send in to CVL the blood samples from animals that might have BSE...all very odd when they say there is no method of diagnosis. Presumably various groups think they might have one.
Four Israeli scientists have urged that all Jewish residents of Libyan or Tunisian origin should undergo a blood test to identify carriers of Creutzfeldt-Jakob disease (CJD) before they may donate blood or organs.
Although the fatal genetic disease affects one in a million of the general Israeli population, it is 100 times more common among these ethnic groups. Professor Amos Korczyn, a leading neurologist at Tel Aviv University's Sackler School of Medicine and Ichilov hospital, and three colleagues have sent an "urgent policy statement" to the Israeli health ministry.
There are around 1000 Israeli carriers of CJD and about 30000 Israelis of Libyan or Tunisian origin. The statement says that, although there are fewer than 20 cases of CJD each year, the disease may nevertheless be passed on during blood transfusion or organ donation or by using implements for neurosurgery that have not undergone special sterilisation.
Professor Korczyn said that, although the disease derives from a genetic mutation, carriers could infect others under certain circumstances. He said that, though the risk of transmission in the blood supply is highly unlikely-and not one case has been documented-all Israeli Jews of Libyan or Tunisian origin (even those of second or third generation) should be required to undergo a blood test, and carriers should be barred from donating blood or organs.
The records of all patients with CJD should also be checked to see if they had ever received a blood transfusion. He said that the matter should be dealt with seriously even though it could arouse political controversy. Last year there was an uproar over the refusal to use blood donated by Ethiopian Jewish immigrants because of concern about potential HIV infection.
Early CJD cases were worrisome, especially since some were in abbatoire workers (Transfusion, 34:915-928, 1994) and considered BSE to human transmissions not so unlikely as my colleagues in our article on TSEs (Encyclopedia of Virology, 1994,1361-9; ed RG Webster). Steven can fill you in on my less circumspect opinion that BSE could infect humans from 1989 onwards.
Be aware that now that BSE is established in humans, it should be more readily transmitted, especially by surgical and dental procedures (article to come out in J. NeuroVirology next month). Nonetheless, you will still find those who poo-pooh the evidence for viremia (first published in 1978 in Science by our lab and subsequently confirmed by others) and the warning that medical materials could be a source of spreading infections (a preview of the growth hormone cases that subsequently developed ... and are still showing up 30 years after exposure.