Implementing a probabilistic definition of freedom from infection to facilitate trade of livestock: putting theory into praxis for the example of bovine herpes virus-1.

International trade of livestock and livestock products poses a significant potential threat for spread of diseases, and importing countries therefore often require that imported animals and products are free from certain pathogens. However, absolute freedom from infection cannot be documented, since all test protocols are imperfect and can lead to false-negative results. It is possible instead to estimate the "probability of freedom from infection" and its opposite, the probability of infection despite having a negative test result. These probabilities can be estimated based on a pre-defined target prevalence, known surveillance efforts in the target population and known test characteristics of any pre-export test. Here, calculations are demonstrated using the example of bovine herpes virus-1 (BoHV-1). In a population that recently became free of BoHV-1 without using vaccination, the probability of being infected of an animal randomly selected for trade is 800 per 1 million and this probability is reduced to 64 (95% probability interval PI 6-161) per 1 million when this animal is tested negatively prior to export with a gB-ELISA. In a population that recently became free of BoHV-1 using vaccination, the probability of being infected of an animal randomly selected for trade is 200 per 1 million, and this probability can be reduced to 63 (95% PI 42-87) when this animal is tested negatively prior to export with a gE-ELISA. Similar estimations can be made on a herd level when assumptions are made about the herd size and the intensity of the surveillance efforts. Subsequently, the overall probability for an importing country of importing at least 1 infected animal can be assessed by taking into account the trade volume. Definition of the acceptable level of risk, including the probability of false-negative results to occur, is part of risk management. Internationally harmonized target prevalence levels for the declaration of freedom from infection from selected pathogens provide a significant contribution to the facilitation of international trade of livestock and livestock products by allowing exporting countries to design tailor-made output-based surveillance programs, while providing equivalent guarantees regarding the probability of freedom from infection of the population. Combining this with an approach to assess the overall probability of introducing at least 1 infected animal into an importing country during a defined time interval will help importing countries to achieve their desired level of acceptable risk and will help to assess the equivalence of animal health and food safety standards between trading partners.

Assessment of viral presence in semen and reproductive function of frozen-thawed spermatozoa from Pallas' cats (Otocolobus manul) infected with feline herpesvirus.

Although herpesviruses are known to contaminate the semen of several mammalian species, the occurrence of feline herpesvirus type 1 (FHV-1) in semen of infected cats has not been reported. Our objectives in this study were to investigate the presence of FHV-1 DNA in seminal fluid and frozen-thawed spermatozoa from FHV-1 infected Pallas' cats (Otocolobus manul) and assess the functionality of their frozen-thawed spermatozoa in vitro. Over a 3-yr period, semen (n = 33 ejaculates) was collected periodically via electroejaculation from four Pallas' cats chronically infected with FHV-1. Spermic ejaculates were frozen by pelleting on dry ice and stored in liquid nitrogen. After thawing, sperm motility and acrosome status were assessed over time during in vitro culture. For vitro fertilization (IVF), viable domestic cat (Felis silvestris catus) oocytes were inseminated with frozen-thawed Pallas' cat spermatozoa and evaluated for embryo cleavage. For FHV-1 polymerase chain reaction (PCR) analysis, DNA was extracted from seminal fluid, frozen-thawed spermatozoa, inseminated oocytes, heterologous IVF embryos, and conjunctival biopsies and analyzed for presence of a 322-base pair region of the FHV-1 thymidine kinase gene. Immediately post-thaw, sperm motility and percentage of intact acrosomes were decreased (P < 0.05) compared to fresh samples, and declined further (P < 0.05) during culture. However, all frozen-thawed IVF samples were capable of fertilizing domestic cat oocytes (overall, 46.1 +/- 6.0% cleavage). PCR analysis did not identify FHV-1 DNA in any reproductive sample despite the repeated detection of FHV-1 DNA in conjunctival biopsies. These results suggest that semen collected from Pallas' cats infected with FHV-1 does not contain cell-associated or non-cell-associated virus and that frozen-thawed spermatozoa exhibit adequate function for potential genetic rescue with minimal risk of FHV-1 transmission.

Low socioeconomic status and risk for infection with human herpesvirus 8 among HIV-1 negative, South African black cancer patients.

Between January 1994 and October 1997, we interviewed 2576 black in-patients with newly diagnosed cancer in Johannesburg and Soweto, South Africa. Blood was tested for HIV-1 and HHV-8 antibodies and the study was restricted to 2191 HIV-1 antibody-negative patients. We examined the relationship between infection with HHV-8 and sociodemographic and behavioural factors using unconditional logistic regression models. Of the 2191 HIV-1 negative patients who did not have Kaposi's sarcoma, 854 (39.1%) were positive for antibodies against the latent nuclear antigen of HHV-8 encoded by orf73 in a immunofluorescence assay. Infection with HHV-8 was independently associated with increasing age (P trend = 0.02). For females, independent risk factors also included working in a paid domestic capacity (OR 1.63, 95% CI 1.09-2.44, P = 0.02), defining occupational status as economically non-active unemployed (OR 1.70, 95% CI 1.06-2.72, P = 0.03), having a state pension or being on a disability grant (OR 1.49, 95% CI 1.05-2.11, P = 0.02), using oral contraceptives (OR 1.43, 95% CI 1.03-1.99, P = 0.03) and having a delayed age at menarche (P trend = 0.04). The relationship between these variables and HHV-8 antibody status requires further, prospective study.

Risk assessment for release of genetically modified organisms: a virus to reduce the fertility of introduced wild mice, Mus domesticus.

Risk assessment is a key task in developing genetically modified organisms (GMOs) intended for release into the environment. A risk assessment protocol is described, focusing on genetically modified biological control agents intended to reduce fertility in mammalian pests. The protocol is being applied to development of an immunocontraceptive murine cytomegalovirus vaccine intended to reduce the frequency and extent of costly troublesome plagues of introduced house mice, Mus domesticus, in southern Australia. Success of the agent, including regulatory approval for release to target populations, will depend on demonstrated biosafety, on the biophysical consequences of releasing the agent, and on public perceptions of the consequences and ongoing risks. The proposed risk assessment protocol addresses biosafety and the biophysical and social risks. It elicits perceptions of interaction and risk from the project scientists and from representatives of interested or affected sectors of society. The perceptions are documented for examination interactively in subsequent socially inclusive formal risk assessments. Representatives of the relevant social sectors participate with the scientists, iteratively if needed, in a workshop to assess the risks of releasing the particular GMO into the environment, using a formal inductive procedure, GENHAZ, designed specifically for assessment and management of the risks of GMOs. Use of this protocol is intended to precede and complement risk assessment and risk management procedures specified by gene technology legislation and regulations.

Yield and future issues of nucleic acid testing.

Despite the much lower actual yield than that estimated for hepatitis C virus (HCV) and human immunodeficiency virus (HIV) nucleic acid testing (NAT)-only positives in the USA and Germany, look-back procedures have revealed that no HCV transmission has occurred in Germany since the introduction of NAT. This indicates sufficient sensitivity of the pool-PCR approach. The slow ramp-up of hepatitis B virus (HBV) however, may require a different approach. It has been shown in Germany that the pooling of samples followed by virus enrichment results in a significant yield. Single donation testing for HBV would not increase the yield, because virus enrichment from mini-pool results in a similar sensitivity to that of single donation testing. Both strategies may be useful for extending future NAT to HBV screening. New candidate viruses for NAT are Parvo B19 and hepatitis A virus (HAV) because of their extreme resistance to inactivation procedures. Their low pathogenicity and epidemiologic characteristics, however, make them candidate viruses only for pooled source plasma. The main future issues of NAT will be related to the automation of pooling, extraction and amplification as a single homogeneous process. Depending on the throughput, automated single donation NAT as demonstrated by the 'Tigris' system may be an option, as far as all transfusion-relevant viruses will be included. In the near future high throughput systems will rely on pooled donor samples, most probably in conjunction with efficient enrichment procedures. For these systems, automation of the extraction and amplification process will be one of the first steps. These procedures will also limitthe costs of NAT and keep it available for use with future candidate viruses.

[Risk and economics of disease introduction to dairy farms]. / Risico en economie van insleep van ziekten op melkveebedrijven.

A more closed farming system will enhance the success of disease eradication programmes, because the introduction or re-introduction of infectious diseases is less likely. The objective of the study was to obtain input for the development of an on-farm decision support model to calculate the economic consequences of a more closed farming system. The input was based on bovine herpesvirus 1 (BHV1), since there were numerous data on this disease, but a more closed farming system will prevent introduction of other diseases as well (i.e. bovine virus diarrhoea virus (BVDV), L. hardjo, and S. dublin). Direct animal contacts, such as purchase of cattle, participation in cattle shows, and cattle that escape and mingle with other cattle, were found to be important risk factors for the introduction of BHV1. Furthermore, the use of protective farm clothing was found to be an important preventive factor. The effect of an IBR outbreak at an IBR-free farm on milk production caused limited losses of on average 0.9 kg per cow per day during 9 weeks, but the variability was high (95% CI 0-2 kg). Nine percent of Dutch IBR-free dairy farms that were also at risk for BVDV, L. hardjo or S. dublin had one introduction per year of one of these four diseases. All these results were incorporated in the economic model. Management measures to reduce the probability of introduction of BHV1, the costs of these measures, and the risk reduction after these measures were obtained from other sources. The calculations showed that the implementation of a more closed system will be profitable for most farms. The profitability will increase when a farm is at risk for more diseases, but will decrease when farms are limited in their facilities to rear replacement heifers or when a large proportion of pasture adjoins pasture of other cattle farms.

The significance of the blood-borne viruses: blood banking and transfusion medicine.

Most of the blood-borne infections that have held our attention during the last half of this century have been well characterized. Although HIV and the hepatitis viruses have enormous world-wide public health implications, there has been considerable success in their prevention of transmission by transfusion. The technology is available to treat and eliminate from virtually all non-cellular blood products the transmission of disease caused by those viruses for which we have had the greatest concern. However, for the cellular blood products the basic methods of prevention continue to be imperfect: donor selection and viral serological testing. The significance of the transmission of blood-borne agents by these products depends upon the frequency of the agent in the donor population and the serological screening performed. There is a marked degree of variation in frequency of these infections, dependent upon geography, living conditions, and life style. Data on the frequency of transfusion-transmitted disease are meagre and usually based upon indirect estimates. In the United States the frequency of the transmission of HIV by cellular blood products is estimated to be 1:125,000 products transfused. A similar estimate for the transmission of hepatitis is 1:200 products transfused. For the developing countries, some of which experience the highest rates of hepatitis and HIV infection in their populations, data on the frequency of transfusion transmission are not generally available. In recent years, new evidence has stimulated interest in a few transfusion-transmissible diseases that, although uncommon from the public health perspective, have both real and potential transfusion impacts for the use of plasma and plasma derivatives as well as cellular products.(ABSTRACT TRUNCATED AT 250 WORDS)

Latex and vinyl examination gloves. Quality control procedures and implications for health care workers.

In December 1987, we investigated an increased number of cases of herpetic whitlow in medical intensive care unit nurses who routinely gloved for secretion contact. One particular brand of vinyl examination glove had been used in the medical intensive care unit. Restriction endonuclease mapping established the similarity of employee isolates with one patient isolate of herpes simplex virus type I. When initial viral assay demonstrated 2.5% to 10% penetration of herpes simplex virus type I across unused gloves, an evaluation of glove quality was undertaken. In a 300-mL watertightness test, seven brands of vinyl gloves failed 4% to 28% (average, 11.1%; 132/1200), while seven brands of latex gloves failed 0% to 2.6% (average, 1.4%; 24/1750). The brand of vinyl glove that had been in use in the medical intensive care unit failed 28% of the time. Watertight gloves were then tested for permeability to herpes simplex virus type I. None of the latex gloves failed (n = 1726), while only 10 of the vinyl gloves failed (n = 1068, 0.95%). Extreme variability in glove quality was observed. However, gloves made from intact vinyl may provide similar protectiveness as those made from intact latex. As the demand for gloves increases, emphasis should be placed on the production of plentiful, better quality latex and vinyl gloves.