Viral Pathogenesis and Virulence the Surface of the Neurone the Virus Attached

194 Nature Vol. 280 19 July 1979

1978). Of 88 non-herbaceous species found capacity to withstand water stress. the molecular level, in the functioning of the peptides and nucleic acids of which along a 1,300-m elevation gradient, 22 were The greater competitive success of C3 viruses are made. B. Fields (Harvard CAM, three were C4 and the remaining 63 species in higher altitude, more mesic • has now been Medical School) gave an example of what were C3 Ten samples were taken at 150-m conditions in the tropics altitude intervals; density, frequency and demonstrated by Tieszen, Senyimba, can be done, when he described his study of area cover values were used to determine an lmbamba and Troughton (Oecologia, two pairs of genes, represented by the importance value for each species at each Berl. 37, 337; 1979) along an altitudinal RN As S 1and M2 of reoviruses types I and elevation. The main peak in the importance and moisture gradient in Kenya. They have 3. He studied parent viruses and a of CAM species was found to occur at low found that nearly all the grass species of the collection of recombinants (or reassortants) and showed that S1 nucleic altitude, that of C3 species at higher low altitude grasslands in Kenya are of a C3 Some grass tribes, acid specifies the haemagglutinin protein altitudes and the C 4 peak was intermediate photosynthetic type. between the other two. Eickmeier such as Paniceae and Andropogoneae of the virus and that this is responsible for ) the ability to agglutinate red cells and for considers this sequence to reflect both the (both exclusively C4 were most frequently adaptational significance of the encountered at intermediate altitudes. The serological specifity. It is also responsible for cell tropism in the animal, so that the physiological variations and also the exclusively C3 tribes (such as Festuceae, respective responses to biotic, competitive A veneae and Agrostideae) were found only type 3 virus causes a necrotising factors. For example, the CAM plants are at high altitude. No Ci species were found encephalitis due to a specific attack on the most suited to the low altitude, arid below an altitude of 2,000 m and no C4 neurones. It also determines the extent to environment, where competitive interplay species above 3,000 m. which the virus inhibits DNA synthesis with other plant species may be regarded as Evidently the complex adaptational when absorbed to cells. M2 RNA on the , C and CAM other hand, which is abundant on the minimal (but see Nature op. cit). C3 plants, significance of · C 3 4 he claims are evolutionarily attuned to photosynthetic systems is profoundly surface of the virus particle determines competitive situations with low abiotic influential on the floristic composition of whether the virus resists inactivation by both, having plant communities both on a chymotrypsin. M2 RNA from type 3 makes stress; C 4 plants can cope with potentially high productivity and the biogeographic and an ecological scale. the virus resistant to host enzymes and hence able to infect when given by mouth. Discussion of this work showed that the next step was to determine at which site on Viral pathogenesis and virulence the surface of the neurone the virus attached. This is probably a part of the from D.A.J. Tyrrell chemical matrix which has some other physiological function characteristic of IT is easy to say ''The influenza virus causes however, survive and migrate up to cover neurones. Reassortants were also made influenza", while having really no the villi again, but while they are doing this which were infectious when given by scientific explanation of many of the signs and differentiating into mature mouth, like type 1, and caused central and symptoms of the disease, for instance enterocytes, there are profound nervous system disease, like type 3, and so, the headache or the depressed white blood physiological disturbances - lack of by the oral route, were more pathogenic cell count. This meeting• would have jolted absorption, excess secretion, lack of than either parent. This type of anyone out of such a complacent view and digestive function (for instance the manipulation confirms earlier conclusions also gave some good examples of how splitting of lactose by disaccharidase) - about the functions of the genes. patient, thoughtful research is building a leading to marked diarrhoea, which can kill It is very difficult to evaluate the way in more complete picture of what happens in a piglet from dehydration unless it is which the host defences interact with the some virus infections - how the virus enters treated. On the other hand, another pig virus, sometimes preventing its and spreads through the body, enters cells, coronavirus causes vomiting and wasting multiplication, sometimes causing disturbs their function, interacts with the disease. M. Pensaert and K.L. Andries immunological damage to infected tissue. host defence mechanisms (such as (State University of Ghent) described how For instance, P.A. Neighbour and B.R. interferon or humoral or cellular this virus affects the upper respiratory tract Bloom (Albert Einstein College of immunity) and disturbs normal body and Jung, the tonsil and the jejunum; it Medicine, New York) described some of functions to produce what we recognise as affects the cells of the plexus of Auerbach their work which started when they a clinical disease. and Meissner in the gut and seems to spread analysed why the lymphocytes of patients What seem in the laboratory to be very from them. It spreads through the nervous with multiple sclerosis show an unusual similar viruses may nevertheless produce system to the brain stem and later to the reactivity to measles virus; they tracked either different diseases or similar diseases spinal cord and the rest of the brain. All down the fault to a defect in the ability of by different methods. There was for this was established in great detail by their lymphocytes to produce type I instance a session on coronaviruses, which painstaking serial virus assay and immuno interferon (Neighbour & Bloom Proc. all look the same and are similar in fluorescent microscopy of experimentally natn. Acad. Sci. U.S.A. 76,476; 1979). biochemical composition. Yet the different infected animals. This suggests how the The success of the meeting was obvious, coronaviruses are specific to particular disease develops - probably the virus and there were many other interesting species - mouse coronaviruses never seem spreads from the respiratory tract and gut papers besides those mentioned here, to affect man or vice versa, for example - along peripheral nerves to the brain stem including whole sessions on herpes viruses and sometimes even to a very limited where the lesions give rise to vomiting, and rhabdoviruses. There were clear signs variety of cells in one species. P.A. while the damage to neurones in the that pathogenesis not only holds scientific Bachmann (World Health Organization, plexuses prevents normal peristalsis, interest, but may be a source of practically Munich) described how the coronavirus of leading to wasting. Furthermore, knowing useful knowledge: vaccines and antiviral transmissible gastroenteritis of pigs (TOE) that the virus invades the nervous system treatments do not always work - sometimes affects only the differentiated enterocytes widely, it is not surprising that a virtually because we guess too much and know too of the villi of the small intestine which may identical virus has been recovered from little about the process by which viruses almost disappear. The crypt cells, pigs diagnosed as having encephalitis, and produce disease. 0 so was named haemagglutinating encephalitis virus. *A symposium on Mechanisms of Viral Pathoacncsis and D.A.J. Tyrrell is in the Division of Virulence was held in Munich on 6 and 7 June, 1979 and Explanations of these important and Communicable Diseases, Clinical Research organised by P.A. Bachmann. mysterious tropisms of viruses must lie at Centre, Harrow.