[Feeding habits of raccoon (Procyon lotor) (Carnivora: Procyonidae) in a coastal, tropical wet forest of Costa Rica]

Raccoon (Procyon lotor) food habits were studied at Manuel Antonio National Park, a tropical rain forest in the Pacific coast of Costa Rica from May to December 1987, from September to December 1989 and from January to April 1990. A 134 feces sample size was used to assess the most important items in raccoon diet: two crab species (Gecarcinus quadratus and Cardisoma crassum) with a relative frequency of 0.94 in the rainy season of 1987, 0.76 in the rainy season of 1989 and 0.65 in the dry season of 1990. Fruits were the second category in importance, with relative frequencies of 0.09 for 1987, 0.32 for 1989 and 0.44 for 1990.

Biological and molecular characterization of a pigeon paramyxovirus type-1 isolate found in Argentina

In this report, we describe the biological and molecular characterization of a paramyxovirus type-1 (PPMV-1) isolate found in wild pigeons in an urban habitat in Buenos Aires, Argentina. Of the nine pigeons captured, three were moribund, and the other six showed diarrhea, ataxia, tremor, torticolis, and wing paralysis. The intracerebral pathogenicity index was 1.29, and the amino acid (aa) sequence at the fusion protein cleavage site was 112GRQ KRF117. These characteristics correspond to a virulent Newcastle disease virus isolate. Nevertheless, it was not possible to reproduce the disease in chickens experimentally although the chickens exhibited seroconversion after inoculation. On the other hand, pigeons inoculated with the isolate became sick. These results provide further evidence about the unusual pathogenicity of PPMV-1 for chickens and show once more the need for more biological determinations in these cases to arrive at a final conclusion.

Sex ratio and breeding of white-lipped peccaries Tayassu pecari (Artiodactyla: Tayassuidae) in a Costa Rican rain forest

White-lipped peccaries are non-seasonal breeders in South America, but little is known about their reproduction in Central America. There are few studies about the sex ratio of this species in the field. We studied the reproduction and sex ratio of white-lipped peccaries during 200 hours of field observation of four radiomarked and two unmarked herds, from July 1996 to April 1997, in Corcovado National Park, Costa Rica. Sex ratio data of three additional, radiomarked herds observed in 1998 were also included. We recorded numbers of mountings, presence of newborns and numbers of nursing interactions. The peccaries showed a distinct reproductive seasonality, with one mating peak in February and another in July. The greatest number of newborns and the peak in nursing activity were observed during July and August, when fruit availability for the peccaries was high. The adult sex ratio was significantly female biased (1.4:1-1.8:1), also in contrast with South American populations.

Identification of optimal regions for phylogenetic studies on VP1 gene of foot-and-mouth disease virus: analysis of types A and O Argentinean viruses

An analysis of the informative content of sequence stretches on the foot-and-mouth disease virus (FMDV) VPI gene was applied to two important viral serotypes: A and O. Several sequence regions were identified to allow the reconstruction of phylogenetic trees equivalent to those derived from the whole VPI gene. The optimal informative regions for sequence windows of 150 to 250 nt were predicted between positions 250 and 550 of the gene. The sequences spanning the 250 nt of the 3' end (positions 400 to 650), extensively used for FMDV phylogenetic analyses, showed a lower informative content. In spite of this, the use of sequences from this region allowed the derivation of phylogenetic trees for type A and type O FMDVs which showed topologies similar to those previously reported for the whole VP1 gene. When the sequences determined for viruses isolated in Argentina, between 1990 and 1993, were included in these analyses, the results obtained revealed features of the circulation of type A and type O viruses in the field, in the months that preceded the eradication of the disease in this country. Type A viruses were closely related to an Argentinean vaccine strain, and defined an independent cluster within this serotype. Among the type O viruses analysed, two groups were distinguished; one was closely related to the South American vaccine strains, while the other was grouped with viruses of the O3 subtype. In addition, a detailed phylogeny for type A FMDV is presented.

Association of bovine DRB3 alleles with immune response to FMDV peptides and protection against viral challenge

We have analysed the influence of bovine MHC (BoLA) polymorphism on the immune response and degree of protection induced by peptide vaccines against foot-and-mouth disease (FMD) in cattle. The peptides used for animal immunisation were: A (VP1(138-156)), AT (peptide A linked to VP1(21-40)) and ACT (peptide A, linked to VP1(196-209) and VP1(21-40)). Sixteen different DRB3 types were found among the 46 cattle analysed by PCR-RFLP typing. No absolute correlation was observed, for any type, with the serum neutralising titres (SNT) values and the protection induced. However, among the most common haplotypes present, associations were observed between expression of different types with the levels of SNT and/or protection induced by peptides A and ACT. Thus, types DRB3.2*1, 3 and 7 were associated with increased levels of protection. In contrast, types DRB3.2*12 and 18 were associated non-protection, and DRB3.2*12 was also associated with low SNT titres. Overall, the results indicate that the polymorphism in BoLA class II molecules affects both the immune response and protection induced by potential FMD peptide vaccines.

Development of chick cardiomyocytes: modulation of intermediate filaments by basic fibroblast and platelet-derived growth factors

Recent studies suggest that peptide growth factors play a functional role in cardiac muscle. To test whether embryonic cardiac muscle is a target for regulation by basic fibroblast growth factor and platelet-derived growth factor, we analyzed the effects of these peptides on the expression of the intermediate filaments desmin and vimentin at the subcellular level during development. Sodium dodecyl sulfate-gel electrophoresis, immunoblotting and fluorescence-activated cell sorting analysis were used to study the effect of basic fibroblast growth factor and platelet-derived growth factor on cultures of chick cardiomyocytes during development. Cytoplasmic and cytoskeletal concentrations of desmin and vimentin were dependent on the stage of embryonic development and on the type of growth factor added to the culture. The most significant finding was the increase in desmin expression in the cytoplasmic and cytoskeletal compartments after treatment with basic fibroblast growth factor (10 ng/ml) of chick heart cells at Hamburger and Hamilton stage 19. In more mature stages, basic fibroblast growth factor did not modify the levels of desmin expression. However, this factor led to a progressive deceleration in the rate of increase in vimentin expression. Platelet-derived growth factor increased vimentin expression in all stages studied, the greatest increases appearing in early stages of heart development. Our findings support the hypothesis that basic fibroblast growth factor plays a role in cardiomyocyte differentiation during the early stages of development, whereas platelet-derived growth factor has a dedifferentiating effect.

Acipimox, a nicotinic acid analog, stimulates growth hormone secretion in short healthy prepubertal children

Recent studies in adult volunteers have demonstrated that the free fatty acid reduction induced by acipimox, a nicotinic acid analog, stimulated GH secretion per se and enhanced in an additive manner the GH secretion elicited by such different stimuli as pyridostigmine, GHRH and GHRP-6. In order to evaluate whether acipimox administration stimulates GH secretion in prepubertal children, we administered a single oral dose of acipimox (100 mg for children weighing <30 kg and 200 mg for those >30 kg) to 14 healthy prepubertal children with a mean age of 8.2 +/- 1.9 years, a mean bone age of 6.2 +/- 3.0 years, growing along the 5-10th percentiles, and with normal thyroid function and IGF-I levels. Acipimox administration elicited a sustained increase in GH from a mean baseline level of 0.6 +/- 0.4 to 6.7 +/- 2.4 microg/l at the end of the test (p<0.05), with a mean GH peak of 10.5 +/- 3.5 microg/l. GH release was delayed so that peak GH levels were achieved 180 minutes after acipimox administration. In order to determine whether acipimox was capable of enhancing the GH secretion elicited by levodopa (L-Dopa), we administered either oral L-Dopa (250 mg for children weighing <30 kg and 500 mg for those >30 kg) or oral acipimox plus L-Dopa to the same children on different days. GH concentrations increased in a similar fashion following either of these tests (from a baseline level of 1.2 +/- 0.4 and 0.7 +/- 0.4 microg/l to 8.4 +/- 2.7 and 9.3 +/- 2.9 microg/l at the end of the test (p<0.001), with peak GH concentrations of 13.1 +/- 4.1 and 11.8 +/- 3.3 microg/l after L-Dopa or acipimox plus L-Dopa, respectively). Although the peak GH concentrations obtained after the combined administration of acipimox plus L-Dopa were similar to those obtained after either acipimox or L-Dopa administration, a larger number of our patients reached a GH cut-off point of >7 microg/l following combined therapy than with either stimulus alone (13/14 patients with combined therapy and 10/14 with acipimox alone). No side effects other than mild facial flushing were noted after acipimox administration. These results indicate that: 1) following the administration of a single oral dose of acipimox, significant GH secretion was elicited in healthy short prepubertal children; 2) the combined administration of acipimox plus L-Dopa did not, however, enhance the GH secretion of this group of children; 3) acipimox was well tolerated with minimal side effects; and 4) further studies in both GH sufficient and GH deficient children are necessary to evaluate acipimox's usefulness in assessing GH reserve.

[Seasonal diet of Tayassu pecari (Artiodactyla: Tayassuidae) in Corcovado National Park, Costa Rica ]

The diet of the white-lipped peccari Tayassu pecari was studied from July 1996 to April 1997 in Corcovado National Park, Costa Rica, through fecal analysis and direct observations. The feces consisted of 61.6% fruits, 37.5% vegetative parts, 0.4% invertebrates and 0.5% unidentified material. These proportions are similar to those reported for white-lipped peccaries diet in South America, but the species consumed were different. In Corcovado, the white-lipped peccary fed on parts of 57 plant species (37 of them fruits). Moraceae was the most represented family. In contrast, the diet of the Peruvian Amazon peccary primarily consists of plant parts (Arecaceae). Costa Rican peccary diet consisted of vegetative parts from Araceae and Heliconaceae. Direct observation showed that peccaries spent 30% of feeding time rooting. Samples taken from rooting sites suggest that peccaries fed on earthworms. Diet differed between months, seasons and habitats. They ate more fruits in coastal and primary forests and more vegetative parts in secondary forest. In the months Octubrer and November the consumption of vegetative parts exceeded fruit consumption.

Protective immunity against foot-and-mouth disease virus induced by a recombinant vaccinia virus

We report the construction of a recombinant vaccinia virus expressing the precursor for the four structural proteins of FMD virus (FMDV) (P1) strain C3Arg85 using a procedure for isolation of recombinant vaccinia viruses based solely on plaque formation. Adult mice vaccinated with this recombinant vaccinia virus elicited high titers of neutralizing antibodies against both the homologous FMDV and vaccinia virus, measured by neutralization assays. Liquid phase blocking sandwich enzyme-linked immunosorbent assays (ELISAs) using whole virus as antigen showed high total antibody titers against homologous FMDV, similar to those induced by the conventional inactivated vaccine. When ELISAs were carried out with heterologous strains A79 or O1Caseros as antigens, sera from animals vaccinated with the recombinant virus cross-reacted. Mice boosted once with the recombinant vaccinia virus were protected against challenge with infectious homologous virus. These results indicate that recombinant vaccinia viruses are efficient immunogens against FMDV when used as a live vaccine in a mouse model.

[Patient classification systems in intermediate and long-term stay institutions: evolution and future perspectives]

The importance of long term care sector is increasingly growing. Actually, the use of patient classification systems is a useful tool for the planning and management of health services for chronic and geriatric patients. Despite being much less known, patient classification systems have had a richer and earlier development in the long term care sector than in the acute care sector. Thus, one could could see the evolution from classifications based on the assessment of functional dependency to classifications progressively including variables corresponding to clinical complexity, and finally to complex systems such as RUG-III. Patient classification systems were first utilised as tools for the financing of long term centres, based on the patients' characteristics. Later, their applications have spread out to objectives related to the management of centres, assessment of quality of care, staff allocation level, control of access and national policies. In Spain, the only experience in the use of a patient classification system is the one used by the Catalan Health Care Administration which uses a classification for the financing of their centres.

Newcastle disease virus surveillance in Argentina: use of reverse transcription-polymerase chain reaction and sequencing for molecular typification

Newcastle disease virus (NDV) remains a major pathogen of poultry where highly virulent strains require reporting to the Office of International Epizootes. NDV is a paramyxovirus existing as different strains classified on the basis of severity of the disease they cause. The present study was conducted in Argentina to determine the prevalence of highly virulent velogenic NDV strains in commercial poultry farms. Tracheal and cloacal swabs from 693 flocks, representing 14% of the broiler production, were collected and pooled. A pool amplified twice in embryonated eggs presented a limited hemagglutination titer. We performed reverse transcription coupled to polymerase chain reaction to amplify fusion and matrix protein gene sequences of the isolate and the strain Trenque Lauquen, isolated in Argentina during an outbreak in 1970-71 and previously characterized as velogenic viscerotropic by biological methods. The amino acid sequences were deduced from nucleotide sequences of the amplification products and the pathotype predicted according to the sequences obtained. From the samples analyzed, we found only one type of NDV, being the isolate identified as lentogenic NDV. This strain is probably the one used in vaccination of flocks where that sample was obtained. These data have allowed us to consider a velogenic NDV-free status in Argentina's commercial poultry.

Optimization of the tyrosinase mRNA probe to detect circulating melanocytes with reverse transcription and polymerase chain reaction

It was recently suggested that reverse transcription polymerase chain reaction (RT-PCR)-based detection of tyrosinase messenger RNA (mRNA) in peripheral blood is useful in the early detection of circulating tumor cells, since tyrosinase is thought to be a melanocyte-specific marker. However, the sensitivity of detection of these cells in circulation is controversial, some authors reporting 0% effectiveness, others obtaining 100% efficacy. We developed a modification of a technique to process blood samples to detect tyrosinase mRNA, and tested the method with 50 samples from as many patients with histologically confirmed malignant melanoma in different stages. Whole blood was processed by discarding the plasma and extracting RNA from density gradient-isolated peripheral blood lymphocytes. The RNA samples were tested with a sensitive nested primer RT-PCR assay. Sensitivity was tested using RNA extracted from SK-mel-1 human melanoma cells diluted serially with peripheral blood obtained from healthy control subjects. A lymph node from a patient with confirmed disseminated melanoma served as the positive control. Our technique was able to detect tyrosinase mRNA in samples from the 37 patients with progressive metastatic melanoma. The test detected tyrosinase mRNA from both the melanoma cell line and the positive lymph node. Our method to extract RNA from whole blood improves the specificity and sensitivity of tyrosinase mRNA detection by RT-PCR. The test should be of use in determining the prognosis of patients with melanoma, and in deciding when to initiate early treatment in patients with malignant melanoma.

[The health costs of alcoholism]

OBJECTIVE

To evaluate the economic effect in terms of health costs of alcohol abuse in Spain.

DESIGN

The most up-to-date available, secondary sources of information were used. The period for the costs calculation was a natural year, with the prices adjusted to pesetas in 1996. The focus was based on the prevalence of cases per period. All the information referred to the whole of Spain.

SETTING

Health costs were broken down into out-patient attendance, hospital emergencies, admissions, treatment at special centres and other health expenditure.

MEASUREMENTS AND MAIN RESULTS

The total health cost attributable to alcoholism was 177,084 million pesetas, broken down as follows: a) cost of hospital admissions: 93,644 million pesetas (52.88%); b) cost of out-patient attendance: 34,600 million (19.53%); c) cost of treatment at special centres: 18,029 million (10.18%); d) cost of hospital emergencies: 10,481 million (5.91%); and e) other health expenditure: 20,330 million pesetas (11.48%).

CONCLUSIONS

The figures arrived at do not cover the total cost of alcohol abuse, since a conservative approach was adopted. They stand as a minimum of the expenditure in our country. Some are direct costs on health authorities, whereas others can be managed as a cost-opportunity problem.

RUG-III and resource allocation: comparing the relationship of direct care time with patient characteristics in five countries

BACKGROUND

resource use by different types of patients is of increasing interest to health care services all over the world. Case-mix systems that group together individuals with similar patterns of resource use have been developed to address these questions. Resource Utilization Groups version III (RUG-III) was developed in the USA to address the issue in the care of elderly people and has been validated in a number of countries.

METHOD

this paper synthesizes the results of RUG-III validation studies performed in the USA, Japan, Spain, Sweden and England and Wales, showing the consistency of the system in spite of different skill-mix and total time spent with patients. Data from the validation studies of five countries were compared. Percentage of time given by trained nurses and mean nursing time per patient was compared overall and between selected RUG-III groups.

RESULTS

mean time per patient ranged from 84.4 min per day in Japan, to 155.6 min in England and Wales. Trained nurse time ranged from 7.5% of total time in the USA to 53.2% of total time in England and Wales. The inter-group relationship was very similar in all countries. The RUG-III system appears robust in a wide variety of settings and countries. Future research should address the relationship between skill-mix and total time spent with patients with respect to outcome and quality of care.

Thoracic infection after trauma

Thoracic infections following injury are common, with pneumonia and empyema being the most prevalent. Pneumonia may follow all types of injury, and empyema occurs most frequently after chest injuries. Mediastinitis, lung abscess, and pericarditis occur rarely in the trauma patient. An organized approach to diagnosis and treatment is essential in the management of these problems.

A large-scale evaluation of peptide vaccines against foot-and-mouth disease: lack of solid protection in cattle and isolation of escape mutants

A large-scale vaccination experiment involving a total of 138 cattle was carried out to evaluate the potential of synthetic peptides as vaccines against foot-and-mouth disease. Four types of peptides representing sequences of foot-and-mouth disease virus (FMDV) C3 Argentina 85 were tested: A, which includes the G-H loop of capsid protein VP1 (site A); AT, in which a T-cell epitope has been added to site A; AC, composed of site A and the carboxy-terminal region of VP1 (site C); and ACT, in which the three previous capsid motifs are colinearly represented. Induction of neutralizing antibodies, lymphoproliferation in response to viral antigens, and protection against challenge with homologous infectious virus were examined. None of the tested peptides, at several doses and vaccination schedules, afforded protection above 40%. Protection showed limited correlation with serum neutralization activity and lymphoproliferation in response to whole virus. In 12 of 29 lesions from vaccinated cattle that were challenged with homologous virus, mutant FMDVs with amino acid substitutions at antigenic site A were identified. This finding suggests the rapid generation and selection of FMDV antigenic variants in vivo. In contrast with previous studies, this large-scale vaccination experiment with an important FMDV host reveals considerable difficulties for vaccines based on synthetic peptides to achieve the required levels of efficacy. Possible modifications of the vaccine formulations to increase protective activity are discussed.

Effectiveness and limitations of the use of the gonadotropin-releasing hormone agonist leuprolide acetate in the diagnosis of delayed puberty in males

In order to evaluate the effectiveness of the gonadotropin-releasing hormone agonist leuprolide acetate in distinguishing gonadotropin deficiency from delayed puberty, a single subcutaneous dose of 20 micrograms/kg of leuprolide acetate was administered at 07.00 h to 14 patients with constitutionally delayed puberty and to 8 gonadotropin-deficient subjects, and serum gonadotropin and testosterone levels were determined at baseline and 1,2,3,6,12, and 24 h thereafter. The increase in gonadotropin and testosterone levels was significant in patients with delayed puberty, so that the mean peak luteinizing hormone and to a lesser degree the mean peak testosterone levels clearly differentiated normally delayed from gonadotropin-deficient puberty. However, when the peak gonadotropin and testosterone concentrations were analyzed individually, there was a considerable overlap between the two groups of males, limiting the usefulness of this test.

The safety and effectiveness of stepwise and low-dose administration of follicle stimulating hormone in WHO group II anovulatory infertile women: evidence from a large multicenter study in Spain

PURPOSE

Our goal was to investigate the safety, effectiveness, and feasibility for the practicing physician of stepwise and low-dose administration of FSH in WHO group II anovulatory infertile women.

METHODS

Infertile female patients (n = 234) suffering from WHO group II anovulation, and who failed to became pregnant with clomiphene citrate, were included in a multicenter, prospective, clinical study of treatment with a protocol of chronic low-dose and small incremental rises with urinary purified or highly purified FSH. Follicular development was monitored with ultrasonographic scans.

RESULTS

The 234 patients received a total of 534 cycles of treatment, for a mean number of 2.3 treated cycles per patient. hCG was withheld in 65 (12.2%) cyles because of no response and in 28 (5.2%) cycles because of hyperresponse. Of the remaining 441 cycles, 419 (95%) were ovulatory, and in 198 (47.3%) of these cycles a single dominant follicle developed. There were 93 pregnancies (39.7% per patient), for a cycle fecundity rate of 17.4%. Cumulative conception rate after two treated cycles was 33.5%. There were 14 (15%) pairs of twins and 10 (10.8%) spontaneous miscarriages. The prevalence of complications was low with no cases of severe OHSS. Basal LH/FSH ratio was significantly higher in the pregnant group of patients than in nonpregnant women.

CONCLUSIONS

Stepwise and chronic low-dose administration of FSH is a safe and effective method for treatment of WHO group II anovulatory infertility, mainly in those patients having high LH/FSH ratios.

Prevalence of precancerous lesions of the stomach in Venezuela

Gastric biopsies from 1477 participants in a chemoprevention trial for precancerous lesions of the stomach in Venezuela were evaluated for the prevalence of precancerous lesions and Helicobacter pylori infection. These study subjects were selected from participants in an early detection program for gastric cancer using double-contrast X-ray. Overall, 94% had some type of chronic gastritis (CG) and were positive for H. pylori using Giemsa stain, 49% had atrophic gastritis, 34% had intestinal metaplasia (IM), and 6.5% had dysplasia. There were only three subjects (0.2%) with normal gastric mucosa, and 4% had only superficial gastritis. The prevalence of all of these precancerous lesions increased with age, but there was no clear difference by gender. The prevalence of the various lesions was higher in the antral mucosa than in the fundic mucosa. H. pylori infection was strikingly frequent in our study population, with prevalence rates ranging from 73% in subjects with superficial gastritis to 95% in those with atrophic gastritis and IM and 98% in those with CG. The prevalence of H. pylori was equally high in males and females, and it was significantly positively associated with the degree of infiltration of poly- and mononuclear cells and with that of active regeneration; it was inversely correlated with the degree of atrophy, IM, and dysplasia. Our findings support the precancerous nature of the various gastric lesions and the etiological role of H. pylori infection in CG.

[Agreement between information supplied by the patient and a family member on medical history, consumption of tobacco, alcohol and coffee and diet in cancer of the exocrine pancreas and extrahepatic biliary tract]

OBJECTIVE

No study on mutations in the K-ras oncogene and cancer of the exocrine pancreas or cancer of the biliary system has analyzed the reliability of clinical and epidemiological information.

METHODS

Agreement between patient and surrogate on factors potentially related to both tumours was evaluated within a multicentre prospective study. Interviews were personally administered to both patient and surrogate (N = 110 pairs). Agreement was examined via the simple kappa index (k), the weighted kappa index (kw), the percentage of simple agreement, and the percentages of positive and negative agreement.

RESULTS

Agreement for medical history was excellent (k between 0.89 and 0.76), as it was for tobacco consumption (k = 0.98). Agreement was moderate for coffee consumption (k = 0.68), frequencies of food groups (kw from 0.66 to 0.38), and consumption of alcoholic drinks (k from 0.66 to 0.32). Surrogates indicated a higher consumption of alcohol than patients.

CONCLUSION

Surrogates can be an alternative source of information when patients cannot be interviewed, but information on alcohol consumption should be treated with caution.

The management information system and change processes in health systems

This report describes a management information system (MIS) designed by PAHO's Health Systems and Services Division in collaboration with technical experts from a number of different countries. This MIS, a methodology currently used at the institutional or national level in more than 21 countries of the Americas, is a strategic and practical instrument that is easy to apply, interpret, and use, and whose purpose is to facilitate fundamental changes in health management. Based on the management concept that inputs, processes, and outputs are quantifiable, the MIS places special emphasis on health system productivity, an essential condition for achieving health coverage that is both adequate and equitable.

Using the handicap code of the ICIDH for classifying patients by intensity of nursing care requirements

An 11-class patient classification system (PCS) has been built on a recode of two dimensions of the handicap code of the ICIDH: physical independence and mobility handicaps. The proposed system, called MAC XI, explains 78% of the variance of nursing care hours required by nursing-home residents and extended-care hospital patients. This percentage of variation is higher than the one explained by traditional dependency grids such as the Exton-Smith, Murphy, Kuntzmann and SMAF. MAC XI, based on two dimensions of the handicap code, is thus a powerful tool for predicting intensity of nursing care for staffing and budgeting purposes in long-term care institutions.

Response of foot-and-mouth disease virus C3 Resende to immunological pressure exerted in vitro by antiviral polyclonal sera

The foot-and-mouth disease virus (FMDV) shows a remarkable antigenic variability. Like other RNA viruses, FMDV has a high mutation rate and it has been proposed that selection exerted by antibodies of the host could play a major role in its evolution. In this work, antiserum-resistant variants of FMDV (Nr variants) were selected upon 25 serial passages of a cloned C3 Resende strain on secondary monolayers of fetal bovine kidney (FBK-2) cells in the presence of subneutralizing levels of antiviral polyclonal sera (APS). After serial passage under immune selective pressure, the five Nr variant populations selected from five independent serial passages--their controls remaining unmodified--acquired the following characteristics: (i) increased resistance to neutralization by APS; (ii) five different antigenic specificities detected by enzyme-linked and neutralization assays using monoclonal antibodies; (iii) the same modification (residue 146, S to L) at the major antigenic site of VP1 (G-H loop, the 135-160 region); and (iv) specific changes for each Nr population outside the major antigenic site of VP1 at residues 46, 48 and 49 of the 40-60 region of VP1 (B-C loop). These results extend our previous work on selection of Nr variants using polyclonal sera, and add new information with regard to antigenic variation, mainly concerning the involvement of the 40-60 region of VP1 in the process of immune selection.