A brief overview of food hygiene legislation.

Following several animal disease outbreaks and food contaminant scandals in Europe in recent years, the European Commission adopted the White Paper on Food Safety in 2000. This White Paper contains a number of recommendations aimed to increase food safety, improve the traceability of food products and regain consumer confidence in the food industry. To this effect a package of new European legislation on food and feed has been prepared with the following characteristics: responsibility of food safety lies with the food business operator, while the competent authority of the Member State verifies correct implementation of the new rules. Production should be based on good hygienic practice and HACCP principles and products are subject to microbiological criteria and temperature limits. The legislation deals with all food and covers the entire food chain ("from stable to table"). The general framework of the new food hygiene legislation is explained. The General Food Law (Regulation (EC) No 178/2002) is discussed in more detail as well as the Regulations concerning food hygiene. The characteristics and requirements of each one of the three Hygiene Regulations is presented (Regulation (EC) No 852/2004, Regulation (EC) No 853/2004 and Regulation (EC) No 854/2004) with a particular emphasis on the changes in the new (horizontal) legislation as compared to the old (vertical) Directives. Implementing measures of the Hygiene Regulations have been published in the form of four Commission Regulations in December 2005. The implementing measures deal with technical issues often in great detail and became applicable at the same time as the Hygiene Regulations with effect of 1 January 2006. The major issues as laid down in the four Commission Regulations are presented. Finally, various guidance documents are mentioned. These documents are available on the Internet site (http//ec.europa. eu/food/food/biosafety/hygienelegislation/guide_en.htm) of DG SANCO and explain in plain language some of the topics of the Hygiene Regulations.

Effect of gamma-irradiation on serum samples on the diagnostic performance of ELISA methods for the detection of trypanosomal antibodies.

The study investigated the effect of gamma-irradiation on bovine serum samples on the ability of enzyme-linked immunosorbent assay (ELISA) methods to detect trypanosomal antibodies. The serum samples were analysed using two standardised indirect ELISA systems. Higher measurement values were observed for most gamma-irradiated antibody positive and negative test samples. Using cut-off points, determined from the analysis of a non-irradiated trypanosomal antibody-negative population, the gamma-irradiated sera data showed that there was an increased risk of misclassifying samples as false positive or cross-reactive due to increased analytical sensitivity and decreased analytical specificity. The intraplate precision and agreement between tested and expected values of measurements were not altered throughout. The impact on the assays' diagnostic performance was estimated by analysing diagnostic sensitivity, diagnostic specificity and related parameters. The data demonstrated that although there was a bias of higher measurement values after gamma-irradiation, this could be compensated after readjustment of the cut-off points to obtain best separation of antibody-positive and -negative samples. Thus, for each assay, no significant difference of the diagnostic proficiency was found before and after gamma-irradiation. The practical implications are discussed of a serum sterilisation procedure using (60)Co gamma-rays for routine sample testing, assay validation and trypanosomosis monitoring and tsetse-fly control and eradication programmes.

Charting methods to monitor the operational performance of ELISA method for the detection of antibodies against trypanosomes.

Four indirect enzyme-linked immunosorbent assays (ELISAs) for the detection of antibody against trypanosomes using antigen-precoated plates (Trypanosoma congolense and T. vivax) were used in 15 veterinary diagnostic laboratories in Africa and Europe. The study provided data allowing an evaluation of charting methods with respect to the operational performance of each ELISA. Data from standardised internal quality control (IQC) samples were plotted on charts and used as the assay performance indicators with reference to expected upper and lower control limits. Based on unprocessed (optical density) and normalised absorbance values (calculated as a percentage positivity of a control), dispersion of values from the expected data range was estimated plotting the location and deviation of the values. In addition, assay precision was estimated plotting the distribution of coefficients of variation<10% of the IQCs. Binding ratios of controls were calculated to estimate the assay proficiency with respect to the accuracy of assessing that the IQC samples tested positive or negative in the test proper. The graphical analysis of dispersion of absorbance values in combination with assay precision and proficiency criteria was considered fully satisfactory to evaluate the operational performance of the ELISAs and provided useful decision criteria for plate acceptance and rejection. The establishment of standardised and transparent IQC data charting methods for the indirect ELISAs provided an increased measure of confidence to national laboratories with respect to their reports on disease occurrence. Moreover, the relative assay performances between all laboratories were examined using summary data charts with reference to the performance criteria described. The IQC data were also examined using modified Youden plot analysis demonstrating that indirect ELISA methods can be successfully applied at diagnostic laboratories in the tropics for monitoring trypanosomosis control programmes.

Evaluation of antigen-coating procedures of enzyme-linked immunosorbent assay method for detection of trypanosomal antibodies.

Research was undertaken to improve the antigen-coating step of indirect enzyme-linked immunosorbent assay (ELISA) method through the use of polystyrene 96-well plates precoated with antigenically stabile crude trypanosomal antigens. The plates were precoated with antigens, air dried and sealed before being packed in plastic bags with silica gel desiccant packets. Such plates stored at +4 and +37 degrees C provided an assay performance, which was superior to that of plates freshly coated with antigens from a frozen stock. Antigen-precoated plates consistently proved stable after storage up to +50 degrees C for at least 1 year. The accuracy of the assay was not affected, i.e. trypanosomal antibody-positive sera were clearly discriminated from trypanosomal antibody-negative negative sera. In contrast, lyophilized trypanosomal antigens lacked stability on storage at +37 degrees C for longer than 1 month. It was concluded that the routine use of antigen precoated polystyrene plates for the enzyme immunoassay technique will contribute to improved assay robustness at an acceptable diagnostic proficiency. The modified coating procedure will also provide an improved quality assurance and standardization procedure for the assay, which is required to allow the reliable detection of trypanosomal antibodies and comparison of data from different laboratories.

Detection of Trypanosoma congolense antibodies with indirect ELISAs using antigen-precoated microtitre plates.

The study reports the performance of four indirect enzyme-linked immunosorbent assays (ELISAs) for antibody (AB) detection using microtitre plates which were precoated with native or heat/detergent denatured antigens (AGs) from Trypanosoma congolense (T.c.) and T. vivax (T.v.), and stored for between 1 to 206 days at +37 degrees C. Bovine serum samples were obtained by sequential bleeding of 3-months old T.c.-infected bulls and their uninfected cohorts, as well as by a single bleeding of uninfected adult cattle. The first day of AB detection, and observations on samples after this (defined as estimated ELISA sensitivity), depended on the cut-off value in the specific ELISAs. Cut-off values from pre- and early post-infection samples of individual animals demonstrated a seroconversion in all ELISAs on average after 10-15 days post-infection (dpi). The AB detection was delayed in the T.c. native and denatured AG-based ELISAs using cut-off points from uninfected cohort cattle (16.5 dpi, 19.3 dpi) and the adult cattle population (22.1 dpi, 25.0 dpi). The T.v. AG-based ELISAs however lacked crossreactiviy to T.c. ABs. The estimated sensitivity of each T.c. AG-based ELISA was above 96% throughout, but significantly lower for the T.c. native AG-based ELISA (91.1%) when the adult cattle derived cut-off point was used (p<0.01). The sensitivity of the phase contrast buffy coat technique was similar to the T.c. AG-based ELISAs, but significantly lower when the T.c. denatured AG-based ELISA was used at the adult cattle derived cut-off point (p<0.05). The implications of the results and future research aspects on ELISAs to detect trypanosomal ABs and AGs are discussed.

Pitfalls in the application of enzyme-linked immunoassays for the detection of circulating trypanosomal antigens in serum samples.

The experimental infection of two goats with Trypanosoma vivax trypanosomes provided samples for analysis using parasitology techniques and antigen-detection enzyme-linked immunosorbent assays (ELISAs) for T. vivax, T. congolense and T. brucei. Clinical, parasitological and serological findings were monitored during the course of infection to identify problems in the application of these ELISAs. The data clearly showed that the ELISAs examined were entirely unsuitable for the reliable detection of trypanosomal antigen. Consequently, research strategies pertinent to the development of a new generation of both antigen and antibody ELISAs are outlined considering the problems encountered. These were (1) the reactivity of the reagents; (2) the specificity of the reagents; (3) the nature of the test sample, e.g. the compartmentalisation of trypanosomes between plasma, serum and red blood cells; (4) possible interference with the ELISA through immune complexing; and (5) the biology of the host/trypanosome relationship to gain an understanding of fluctuations in trypanosomes in the systemic circulation.

Improved methods for the diagnosis of African trypanosomosis.

The diagnosis of trypanosomosis in animals with low parasitaemia is hampered by low diagnostic sensitivity of traditional detection methods. An immunodiagnostic method based on a direct sandwich enzyme-linked immunosorbent assay (ELISA), using monoclonal antibodies, has been examined in a number of African laboratories for its suitability for monitoring tsetse control and eradication programmes. Generally, the direct sandwich ELISAs for the detection of trypanosomal antigens in serum samples have proved to be unsatisfactory with respect to diagnostic sensitivity when compared with traditional parasitological methods such as the dark ground/phase contrast buffy-coat technique. Consequently, antigen-detection systems exploiting various other direct, indirect and sandwich ELISA systems and sets of reagents are being developed to improve diagnosis. In addition, an existing indirect ELISA for the detection of antibodies has been improved and is being evaluated in the field in order to detect cattle that are or have been recently infected with trypanosomes. Developments and advantages of other diagnostic techniques, such as dip-stick assay and tests based on the polymerase chain reaction are also considered.

Study of the effect of gamma-irradiation on bovine serum samples on the ability of monoclonal antibodies to detect invariant antigens of Trypanosoma congolense, T. vivax and T. brucei in enzyme-linked immunosorbent assays.

Samples of bovine serum from uninfected and African trypanosomes-infected animals were tested before and after gamma-irradiation, using three sandwich enzyme-linked immunosorbent assays (ELISA). Each test system utilized a different monoclonal antibody, reputedly allowing the specific detection of conserved-invariant cytoplasmic antigens of trypanonosomes, T. congolense, T. vivax, and T. brucei, respectively. Results have identified two groups of samples. The first contained samples where there were unequivocal ELISA results indicating positivity and negativity, for non-irradiated samples. In this group, irradiation had no effect on the diagnostic sensitivity of the assays. All samples shown to be positive before irradiation remained positive and those shown to be negative, remained negative. There was, however, a statistically significant reduction in signal in each of the ELISAs following irradiation. The second group contained samples identified before irradiation as flanking the diagnostic negative/positive threshold of OD > or =0.05. These showed a negative bias after irradiation of the order of OD -0.01, which was shown to be statistically significant by paired t-statistics. Without correction of the given diagnostic negative/positive threshold, bovine sera with OD values around the threshold were expected to deliver more false negative test results upon irradiation. This was confirmed when serological data were compared with parasitological findings; where three times more false negative test results were found from irradiated serum samples. Consequently, for this group of irradiated bovine samples tested by ELISA, the re-adjustment of the diagnostic negative/positive threshold of the ELISAs using defined irradiated serum samples is recommended; otherwise, the frequency of false negative results might be increased.

Infectious agents associated with diarrhoea of calves in the canton of Tilarán, Costa Rica.

A case-control study of calves under 3 months of age was carried out by weekly visits to 15 farms in the canton of Tilarán, Costa Rica. Most farms were dedicated to beef or dual-purpose (DP) production. Faecal samples were collected over a 6-month period from a total of 194 calves with clinical signs and from 186 animals without clinical signs of diarrhoea as assessed by a scoring system. The samples were investigated for the presence of viruses, bacteria and parasites. Torovirus was detected for the first time in Costa Rica and was present in 14% of calves with diarrhoea and in 6% of the controls. Coronavirus and Rotavirus were less frequently encountered in either one of the groups (in 9 and 7% of scouring calves and in 1 and 2% of controls, respectively). Escherichia coli was detected in 94% of all the faecal samples, but isolates from only three samples from calves with diarrhoea contained the K99 antigen. Similarly, Salmonella was found only in scouring calves. Cryptosporidium oocysts were detected in animals with signs of diarrhoea, while other coccidia oocysts, Strongylida and Strongyloides eggs were frequently found in animals both with and without diarrhoea. A conditional logistic regression (CLR) analysis to compare healthy and scouring calves showed a significant difference with regard to the presence of Torovirus, Rotavirus and Coronavirus.

Seasonal incidence and hemoparasite infection rates of Ixodid ticks (Acari: Ixodidae) detached from cattle in Costa Rica.

To determine the tick species hindering the cattle industry in Costa Rica and to assess infection rates of ticks with three important hemoparasite species, cattle were monitored during a period of six months (October 1992-March 1993). Four farms were located in the dry pacific region of the canton of Tilarán and a fifth farm on the slopes of the Poás volcano in a cool tropical cloud-forest ecosystem. On each farm 3 to 5 animals of 6 to 24 months of age were selected at random. All ticks were removed on a monthly basis from the right half side of each animal, while the site of attachment was recorded. Ticks were counted and differentiated according to species, developmental stage and sex. Moreover, engorged female ticks were assayed for the presence of Babesia bigemina, Babesia bovis and Anaplasma marginale using the polymerase chain reaction (PCR) multiplex system. Two species of ticks, Amblyomma cajennense and Boophilus microplus, were encountered on the cattle in the Tilarán region and one species, B. microplus, was detected in the Poás region. Two to ten times as many ticks were encountered in the Tilarán region than in the Poás region, which is in accordance with a stable enzootic protozoan disease situation in the former region and an unstable epizootic situation in the latter region. Nymphal and adult stages of both tick species were present in largest numbers on the ventral parts of the animals. PCR analysis of entire ticks indicated very high infection rates with hemoparasites of veterinary importance. This was in accordance with high seroprevalence rates in the hosts.

Seasonal incidence and hemoparasite infection rates of Ixodid ticks (Acari: Ixodidae) detached from cattle in Costa Rica

To determine the tick species hindering the cattle industry in Costa Rica and to assess infection rates of ticks with three important hemoparasite species, cattle were monitored during a period of six months (October 1992-March 1993). Four farms were located in the dry pacific region of the canton of Tilar n and a fifth farm on the slopes of the Po s volcano in a cool tropical cloud-forest ecosystem. On each farm 3 to 5 animals of 6 to 24 months of age were selected at random. All ticks were removed on a monthly basis from the right half side of each animal, while the site of attachment was recorded. Ticks were counted and differentiated according to species, developmental stage and sex. Moreover, engorged female ticks were assayed for the presence of Babesia bigemina, Babesia bovis and Anaplasma marginale using the polymerase chain reaction (PCR) multiplex system. Two species of ticks, Amblyomma cajennense and Boophilus microplus, were encountered on the cattle in the Tilarán region and one species, B. microplus, was detected in the Poás region. Two to ten times as many ticks were encountered in the Tilarán region than in the Poás region, which is in accordance with a stable enzootic protozoan disease situation in the former region and an unstable epizootic situation in the latter region. Nymphal and adult stages of both tick species were present in largest numbers on the ventral parts of the animals. PCR analysis of entire ticks indicated very high infection rates with hemoparasites of veterinary importance. This was in accordance with high seroprevalence rates in the hosts

Effects of trypanosome and helminth infections on health and production parameters of village N'Dama cattle in The Gambia.

The effects of trypanosome and helminth infections on health and production parameters in 2000 village N'Dama cattle were assessed periodically. Blood examination showed Trypanosoma congolense and Trypanosoma vivax to be prevalent, while strongylid-type eggs were those most frequently encountered in faecal samples. A distinct seasonal fluctuation was detected for both blood levels of trypanosomes and helminth egg output. Strongylid burden and trypanosome infection had significant negative effects on packed red cell volume levels and body weights mainly in animals of 2-3 years old. Clear indications of an increased susceptibility to trypanosomosis were found in animals affected by helminths. Similarly, animals infected with trypanosomes were more frequently infested with strongyles and egg counts were higher than in cattle in which no trypanosomes were detected.

Productivity of trypanotolerant cattle kept under traditional management conditions in The Gambia.

The productivity of trypanotolerant N'Dama cattle, kept under traditional management conditions in The Gambia, West Africa, was assessed by the regular, monthly collection of health and production parameters in two study areas. The study areas were selected because of differences in tsetse challenge. Performance traits were used to build up an index to estimate the productivity of village N'Dama cattle. The productivity index per 100 kg cow maintained per year varied from 37.2 kg in the study area of Keneba village (with a low tstse challenge) to 21.4 kg for cattle kept near the villages of Tuba and Sambelkunda, an area which had a high tsetse challenge. Average age at first calving was 4.5 or 5.0 years depending on the study area, calving intervals were 623 or 703 days and there was an average 12% loss of body weight in adult females during the dry season. The productivity indices of village N'Dama cattle in The Gambia compare favourably with similar indices for trypanotolerant and trypanosusceptible breeds elsewhere in Africa, and show that even under harsh conditions and with high tsetse challenge, they are able to effectively produce milk and meat for the rural population.

Potential of trypanotolerance as a contribution to sustainable livestock production in tsetse affected Africa.

Tsetse transmitted trypanosomiasis is possibly the major constraint on livestock and agriculture development in Subsaharan Africa. Control of the disease has been based on vector control as well as on the use of trypanocidal drugs to treat or prevent infection in animals. Both control methods are effective but have proven not to be sustainable. Moreover, the development of a vaccine against trypanosomiasis is unlikely to be successful in the near future. On the other hand, trypanotolerant cattle, like the N'Dama can survive and produce in tsetse affected areas without interventions. This taurine breed has been indigenous to Africa for approximately 7,000 years and forms presently about 6% of the bovine population of Africa. Generally the N'Dama are kept in the rural areas by the small-scale farmer as a multi-purpose animal. Recent studies have defined management characteristics and assessed the production potential at the village level and under ranching conditions of N'Dama cattle exposed to various levels of tsetse challenge. Furthermore, experimental infections showed conclusively the superior resistance to the effects of infection of the N'Dama cattle when compared to zebu cattle and have confirmed that trypanotolerance is innate in N'Dama cattle. Studies have been conducted on development of protective humoral and cellular responses, the regulation of parasite multiplication and control of anaemia. These studies provided tools for identifying components of trypanotolerance. The ability to resist the development of anaemia in the face of infection, has shown to be correlated with the capacity to be productive; moreover, PCV values can serve as selection criterium for trypanotolerance. Subsequently, repeatabilities and heritabilities of trypanotolerance and performance traits were estimated.(ABSTRACT TRUNCATED AT 250 WORDS)

The interaction of Trypanosoma congolense and Haemonchus contortus infections in trypanotolerant N'Dama cattle.

The interactions between Trypanosoma congolense and Haemonchus contortus infections were studied in N'Dama calves. A total of 38 N'Dama bulls was divided into four groups and each group infected either with H. contortus 1 week after infection with T. congolense or with T. congolense 4 weeks after infection with H. contortus, or with either infection singly. Parasitological (faecal egg counts, parasitaemia), haematological (packed cell volume, white blood cell counts, albumin) and clinical parameters (body weight change, mortality rate) were compared among the various groups. The results showed a reduced prepatent period and a markedly increased pathogenicity of H. contortus infections in animals with a concurrent T. congolense infection. The most harmful combination was a H. contortus infection 1 week after the T. congolense infection which resulted in a progressive and severe anaemia, accompanied by hypoalbuminaemia, increased weight loss and high mortality. The anaemia induced by dual infections showed a low responsiveness to chemotherapy and in several cases supportive treatment did not help recovery. The results also showed that animals with a concurrent T. congolense and H. contortus infection ran a higher risk of succumbing during the infection, and also during 10 weeks following treatment. Although infections with T. congolense alone produced no clinical signs, they were found to significantly reduce the ability of infected animals to mount a normal response to a subsequent H. contortus infection. It was concluded that the increased H. contortus egg excretion observed in animals infected with both parasites might significantly increase the risk of nematode infections and that the reduced prepatent period might necessitate more frequent anthelmintic treatments. These interactions should, therefore, be considered wherever attempts are made to control these two diseases.

Comparative studies on N'Dama and zebu cattle following repeated infections with Trypanosoma congolense.

Twenty N'Dama and eight zebu cattle were inoculated intradermally with bloodstream forms of a cloned strain of Trypanosoma congolense originating from East Africa. All inoculated cattle became parasitaemic. Zebus showed consistently higher levels of parasitaemia and lower packed red cell volume (PCV) percentages than did N'Damas. Three of the eight zebus required treatment when high numbers of trypanosomes were present in the blood and PCV values dropped below 15 per cent. None of the N'Dama cattle needed treatment. Statistical analysis was performed on the data to assess the variability of parasitaemia and PCV levels before and during infection of the N'Dama cattle. The variation in PCV values was large between individuals during the early stages of the disease and diminished as infection continued. After trypanocidal drug treatment and a recovery period of 14 months, the same animals were inoculated intradermally with T congolense bloodstream forms isolated and cloned in The Gambia. Differences in susceptibility to the ensuing disease were apparent when comparing N'Dama and zebu cattle. Five zebu cattle needed trypanocidal drug treatment, while none of the N'Damas needed drug intervention. Ranking the 20 infected N'Damas according to average PCV levels revealed that the animals responded similarly to both infections.

Trypanosomiasis in cattle in Gambia: incidence, prevalence and tsetse challenge.

The incidence of trypanosome infections, measured by a Berenil Index in experimental herds of 10 Zebu and 10 N'Dama cattle, was compared with tsetse challenge and with the prevalence of parasitaemia in local N'Dama at three villages in Gambia. Tsetse challenge was more strongly correlated with the incidence of parasitaemia in the Zebu than in the N'Dama. There was a strong correlation between prevalence and incidence of infection in the N'Dama. There was no correlation, however, between prevalence of infection in cattle and tsetse challenge unless the data were offset by 3-5 months. The Berenil Index in the Zebu increased at about twice the rate as in the N'Dama under corresponding levels of challenge. It is concluded that whereas incidence of infection in susceptible animals is best measured independently, it can, under stable conditions, be inferred from an assessment of tsetse challenge.