The parasitological and serological prevalence of tsetse-transmitted bovine trypanosomosis in the Eastern Caprivi (Caprivi District, Namibia).

Between August 1995 and June 1997 a survey to determine the distribution of tsetse-transmitted trypanosomosis was conducted in the Eastern Caprivi (Caprivi District, Namibia). A total of 1,481 adult cattle was examined at 33 sampling sites. Direct parasitological diagnostic tests were used and eluted blood spots were screened for the presence of anti-trypanosomal antibodies. Tsetse-transmitted trypanosomal infections were detected in 66 animals (4.5%) from 14 different locations. The parasitological and serological prevalence of trypanosomosis was highest in the Mamili area. Trypanosomosis was virtually absent in the Linyanti/Chobe area and the target barrier along the Kwando River had significantly reduced the prevalence of trypanosomosis in cattle grazing to the east of it. This suggests that anti-trypanosomal antibody prevalence data can be used to evaluate and monitor the effectiveness of tsetse control measures. Survey results suggest that in the Katima Mulilo area, trypanosomal infections were being acquired when cattle grazed along the Zambezi River. Moreover, survey results indicate that tsetse have not been able to establish themselves in the Katima Mulilo area. The parasitological prevalence in a herd and the respective prevalence of anti-trypanosomal antibodies was significantly correlated to the percentage of anaemic animals in that herd. Furthermore, the parasitological prevalence in a herd was positively correlated with the prevalence of anti-trypanosomal antibodies of that herd. It is concluded that the prevalence of anti-trypanosomal antibodies in a herd can be used as an additional indicator of the extent of infection in that particular herd.     

A survival analysis of trypanosomosis diagnostic-test performance under natural infection challenge

Little is known about the time-to-first detection and the time difference (TD) between first parasitological and first serological diagnosis of Trypanosoma spp. infections under natural infection challenge in cattle. The objective of our study was to estimate these measures of "longitudinal aspects" of diagnostic performance and to investigate potential biological factors. Emphasis was on diagnosis at the genus level (Trypanosoma spp.). Twelve N'Dama, 12 Gobra zebu and 12N'DamaxGobra (F1) crossbred cattle (all animals non-infected at the start of the experiment, six male and six female animals in each cohort) were exposed to natural high tsetse challenge in the Niamina East area in The Gambia [Acta Trop. 71 (1998) 57]. The animals were investigated parasitologically (detection of trypanosomes by buffy-coat technique), serologically (detection of T. brucei, T. congolense and T. vivax antigen by enzyme-linked immunosorbent assay (ELISA)) and clinically (packed-cell volume, PCV) over a period of 180 days. The time-to-first detection of trypanosomes, trypanosomal antigen (cut-off as suggested by test supplier) and drop in PCV (subject-based cut-off values) were recorded as outcomes of interest. Thus, incidence was both parasitologically (I(p)), serologically (I(s)) and clinically (I(c)). Recurrent events were not considered. The TD between first parasitological and first serological detection was established as I(s) time minus I(p) time. The effect of breed and sex on the time-to-first detection and on TD was investigated using Cox (proportional hazard) regression and ANOVA, respectively.We found that time-to-first parasitological detection of trypanosomosis in N'Dama animals was significantly longer than in the two other breeds (Cox regression, P=0.002). A similar but less-strong (P=0.063) effect of breed on time-to-first detection of trypanosomal antigen was found, whereas no breed effect was observed for clinical detection (P=0.432). Sex had no effect in all detection systems. The TD varied between -56 and 115 (mean 28). Marked differences among breeds and between sexes were not observed (ANOVA, P=0.8). We suggest that incidence studies are more suitable for detecting risk factors for animal trypanosomosis than prevalence-based (cross-sectional) studies because the latter often result in misinterpretation of factors that increase the survival time with infection as risk factors.     

Trypanosomiasis challenge estimation using the diminazene aceturate (Berenil) index in Zebu in Gabon

A longitudinal study was conducted within a cattle ranch in Gabon to determine the diminazene aceturate (Berenil) index (DAI) in a group of Zebu, raised under low tsetse density; this measure providing an assessment of trypanosomiasis risk. The objective was to evaluate the trypanosomiasis pressure thus informing trypanosomiasis control methods and cattle management. Twenty female adult Zebu were monitored for 24 weeks during the dry season. Blood samples were collected on a weekly basis and subjected to parasitological and haematological analysis (n?=?480), using the buffy-coat method and the packed cell volume value (PCV), respectively, infected animals were treated with a single intramuscular injection of diminazene aceturate (8 mg/kg). Twenty-nine single infectious events were recorded and a DAI of 1.45 was calculated. Two trypanosome species were identified: Trypanosoma congolense (96.2%) and Trypanosoma vivax (3.8%). The mean PCV value of the infected animals was lower (26.6) compared to non-infected animals (32.0). This study shows that DAI may be a useful tool to assess trypanosomiasis. However, this is a time-consuming method that may be improved by using randomly selected sentinel animals to adapt the chemoprophylactic schemes, hence decreasing the costs and the drug resistance risk.

     

Estimation of trypanosomal status by the buffy coat technique and an antibody ELISA for assessment of the impact of trypanosomosis on health and productivity of N'Dama cattle in The Gambia

The buffy coat/dark ground phase contrast technique (BCT) and an indirect antibody enzyme immunoassay (ELISA) were employed to assess the trypanosomal status of 32 N'Dama cattle, aged 19-28 months, exposed to natural challenge of Glossina morsitans submorsitans and G. palpalis gambiensis. Prior to the start of the investigation animals experienced 9-16 months of tsetse challenge in the study area. Blood and corresponding serum samples were examined monthly for a period of 8 months for patent parasitaemia by BCT and presence of Trypanosoma vivax and T. congolense antibodies by ELISA. In the ELISA, the reactivity of sera to anti-trypanosomal antibodies was expressed in percent positivity (pp). Packed cell volumes (PCV) and body weights were also recorded monthly, and daily weight gain (DWG) computed to assess the impact of trypanosomal status on health and productivity. During the study period, the overall parasitaemic trypanosome prevalence was 3% (6/199), while the serological prevalence was 54.7% (109/199). Both diagnostic tests revealed a predominance of T. vivax over T. congolense infections in N'Dama cattle. Sensitivity of the immunoassay was 83.3%. In T. vivax-parasitaemic cattle, antibodies persisted for 4-6 months after the parasite was detected by BCT. A significantly higher overall mean PCV level was observed in blood samples obtained from cattle found, in any particular month, negative by BCT and ELISA, compared with those blood samples from animals responding serologically positively for anti-trypanosome antibodies. Likewise, mean DWG was significantly higher in cattle found negative for both tests in comparison to animals presenting detectable anti-trypanosome antibodies and those detected positive by both tests. A significant negative relationship was observed between pp values and PCV levels in animals seropositive for T. vivax and/or T. congolense. Similarly, a negative relationship was observed between DWGs and pp values. PCV levels were significantly positively correlated with DWGs. It was concluded that serological screening could provide useful information complementary to that obtained by the use of BCT not only to assess more accurately the trypanosomal status of cattle populations, but also to evaluate the effects of trypanosome infection on animal health and productivity and estimate the trypanosomosis risk.     

The sensitivity of PCR and serology in different Theileria parva epidemiological situations in Rwanda

Theileria parva is the causative agent of a lethal tick-borne disease of cattle occurring in eastern, central and southern Africa. Variations in the sensitivity of the serological and molecular tests with seasonal vector occurrence and discrepancies between low PCR prevalence and high T. parva vector density are a setback to estimate true prevalences. Therefore, the objectives of the present studies were to evaluate (1) the sensitivity of three serological tests (IFAT, ELISA and SELISA) and one molecular test (PCR) in the diagnosis of chronic T. parva infections in four different agro-ecological zones of Rwanda and (2) the effect of tick challenge and animal's age on the sensitivity of PCR. Blood samples from 635 bovines were collected in four agro-ecological zones of Rwanda. All sera were screened using the IFAT, ELISA, SELISA and PCR. The binary results of the four diagnostic tests were introduced separately for each agro-ecological zone in a Bayesian model to estimate the prevalence of T. parva infections and the sensitivity of the four diagnostic tests. All test specificities were set to 100%. The estimated T. parva prevalence was much higher (83–85%) than estimations based on single diagnostic tests. The estimated sensitivity of serological tests was relatively constant and ranged from 57 to 75% in the various areas. The sensitivity of PCR showed more pronounced variations, ranging from 66% in the low T. parva transmission (high land) zones compared to 24% in the highly vector infested (low land) zones. Calves and adult cattle (n = 194) were also sampled in regularly and irregularly dipped herds in the low land region. The apparent T. parva prevalence detected by PCR was significantly higher in calves than in adult cattle and in herds regularly treated with acaricides, while no significant differences were found with IFAT. The conditional probability that a sample was positive at PCR while it was positive at IFAT was significantly lower in adults. The implication of these findings in the use of diagnostic assays for epidemiological studies is discussed.     

Validation of real-time polymerase chain reaction tests for diagnosing feline immunodeficiency virus infection in domestic cats using Bayesian latent class models

The objectives of the current study were to estimate the sensitivity and specificity of three real-time polymerase chain reaction (PCR) tests for diagnosis of feline immunodeficiency virus (FIV) infection in domestic cats, both individually and when interpreted in series with one of two serological tests, separately in populations of cats at low and high risk of being infected with FIV. One PCR test targeted the pol gene and two targeted the gag gene of FIV. For comparison, sensitivities and specificities of the individual serological tests (IDEXX SNAP(?) test and AGEN Simplify(?) test) were also estimated. The study populations consisted of domestic cats thought to be not vaccinated against FIV. Low-risk (males aged 4 years or less and females; n=128) and high-risk (males over 4 years; n=128) cats were selected from those where blood samples were submitted to a commercial clinical pathology service. Bayesian latent class models were used to obtain posterior probability distributions for sensitivity and specificity for each test, based on prior distributions obtained from three experts. Medians of the posterior sensitivity distributions for the PCR tests based on the pol gene and two regions of the gag gene tests ranged from 0.85 to 0.89, compared to 0.89-0.97 for the two serological tests. The medians of posterior specificity distributions for these PCR tests were 0.94-0.96, and 0.95-0.97 for the serological tests. In contrast, the PCR based on one region of the gag gene had lower median sensitivity. Sensitivities of combinations of these serological and PCR tests interpreted in series were low; medians of posterior sensitivity distributions ranged from 0.75 to 0.83. Relative to the low-risk population, median sensitivities in the high-risk population were lower for all tests other than the AGEN Simplify(?) test; specificities were similar in both populations. We conclude that the sensitivities of the two PCR tests based on the pol gene and two regions of the gag gene, respectively, in non-vaccinated cats are probably lower than the sensitivities of the two serological tests we assessed. We do not recommend screening cats whose FIV vaccination status is uncertain with one of these serological tests and then testing positives with one of these PCR tests because in non-vaccinates, the sensitivities of combinations of these serological and PCR tests interpreted in series are low. Assessment of the validity of these PCR assays in FIV-vaccinated cats is required.     

A Bayesian evaluation of six diagnostic tests for foot-and-mouth disease for vaccinated and non-vaccinated cattle

The sensitivity and specificity of six ELISA tests for foot-and-mouth disease (FMD) to discriminate between sero-converted (for non-structural FMD virus proteins) and non-sero-converted cattle were evaluated for vaccinated and unvaccinated cattle. Since none of the tests could be considered as a proper reference test and for about half of the tested sera the true status (sero-converted or not for non-structural proteins, i.e. presence of antibodies) of the animals was unknown, a Bayesian analysis employing a latent class model was used that did not rely on the use of a reference test or gold standard. Prior information about prevalence for subsets of the data and specificity of the tests was incorporated into the analysis. The specificity of the six tests for vaccinated and non-vaccinated cattle ranged from 96 to 99%. For vaccinated cattle, one test stood out with an estimated sensitivity of 94% (95% CI from 89.8 to 98.1%). Second best for vaccinated cattle were two tests with estimated sensitivities of 85% (95% CI from 78.9 to 89.7%) and 92% (95% CI from 86.2 to 95.6%). For non-vaccinated cattle, the sensitivities of these three tests were around 97%. The remaining three tests showed lower estimated sensitivity for vaccinated cattle, ranging from 57 to 79%.     

Evaluation of loop-mediated isothermal amplification (LAMP), PCR and parasitological tests for detection of Trypanosoma evansi in experimentally infected pigs

Six surra negative piglets (6-week-old) were infected with Trypanosoma evansi and two uninfected piglets were used as negative controls. Detection performances of various diagnostic tests (LAMP, PCR and parasitological tests) were compared by analysing blood samples collected weekly over a period of 11 weeks. With a two by two analysis without a gold standard, all methods were 100% specific. MI had the highest sensitivity of 65%, while LAMP, PCR, MHCT and TBS had sensitivities of 45, 33, 38 and 24%, respectively. However, when the analysis was done using MI as a gold standard, the sensitivity of MHCT was the highest at 53% followed by LAMP, PCR and TBS at 49, 44 and 35%, respectively. All methods gave high specificity above 60%. This study validates LAMP as an alternative method for the diagnosis of surra.     

Comparing FAMACHA eye color chart and Hemoglobin Color Scale tests for detecting anemia and improving treatment of bovine trypanosomosis in West Africa

African animal trypanosomosis (AAT) is considered the most important cattle disease in sub-Saharan Africa but its diagnosis in the field is difficult, resulting in inappropriate treatments, excessive delay in treatments and under-treatment. A field study in West Africa investigated the usefulness of anemia in the diagnosis of trypanosomosis. A total of 20,772 cattle blood samples were taken from 121 villages in 3 countries. The average packed cell volume (PCV) of trypanosomosis positive cattle was 23%, versus 28% for negative cattle. In a sub-set of animals, other causes of anemia were investigated showing most of the anemia burden was attributable to trypanosomosis. Anemia was a reasonably accurate indicator of trypanosomosis in the study area, with a sensitivity of 56% and a specificity of 80% and a diagnostic odds ratio of 4.2, the highest of all the signs evaluated (anemia, emaciation, staring coat, lymphadenopathy, fever, lacrimation and salivary or nasal discharge). Having confirmed the usefulness of anemia as a predictor of trypanosomosis, two potential pen-side tests for anemia were evaluated (the first reported trial of their use in cattle), firstly a color chart developed for anemia detection in sheep through visual inspection of conjunctival membranes (FAMACHA) and secondly the Hemoglobin Color Scale (HbCS) developed for assessing hemoglobin levels in human patients by comparing blood drops on filter paper with color standards. In a population of cattle suspected by their owners to be sick with trypanosomosis (n=898) the sensitivity of the HbCS test was 56% and the specificity was 77%, while the sensitivity of the FAMACHA test was 95% and the specificity was 22%. The higher sensitivity but lower specificity suggests the FAMACHA may be useful as a screening test and the HbCS as a confirmatory test. The two tests were also evaluated in cattle randomly selected from the village herd. Using cut-off points to optimize test performance, the HbCS test had a sensitivity of 81% and a specificity of 62% (n=505 cattle), while the FAMACHA had a sensitivity of 92% and a specificity of 30% (n=298 cattle). Recommendations are made for the appropriate use of these tests in the West African region.     

Performance characteristics of an enzyme-linked immunosorbent assay for the detection of liver fluke (Fasciola hepatica) infection in sheep and cattle

AIM: To validate an enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against liver fluke (Fasciola hepatica) in sheep and cattle sera. METHODS: Gold-standard sera from sheep and cattle of known infection status, i.e. sera from non-infected animals and from animals known to be infected with F. hepatica were assayed with a commercially available ELISA and results analysed by ROC analysis. RESULTS: The ROC analysis suggested cut-offs that were considerably lower than those suggested by the manufacturer, yet the ELISA performed with high sensitivity and specificity, 98 to 100%, respectively for sheep and cattle sera. For bovine sera, particularly good discrimination between positive and negative sera was observed. Infection in experimentally infested animals could be demonstrated 7-8 weeks earlier than with classical parasitological techniques. CONCLUSIONS: The analysis of the ELISA's performance demonstrated high sensitivity and specificity. ROC analyses optimised the cut-off point suggested by the manufacturer of the commercial diagnostic assay. Diagnosis of infection with F. hepatica was achieved much earlier than is possible with current parasitological techniques. This could help with the control of fasciolosis, enabling treatment before clinical manifestation of the disease.     

An update of the bovine trypanosomosis situation at the edge of Hluhiuwe-Imfolozi Park, Kwazulu-Natal Province, South Africa

To obtain updated data on and assess the contribution of trypanosomosis to the disease burden of cattle kept at the edge of the Hluhluwe-iMfolozi Park, a survey was conducted at Mvutshini Dip. Use was made of a purposeful sampling strategy by restricting sampling to animals that the livestock owner considered to be in poor condition. Of a total of 76 blood samples collected, 26 were parasitologically positive and 46 were positive on PCR/RFLP. Almost all infections were due to Trypanosoma congolense savannah subgroup. A total of 63 animals had a PCV < or = 24% and were considered to be anaemic. Results from the survey show that trypanosome infections contribute significantly to the overall burden of disease in the area. Further research is required to develop appropriate control methods.     

Prevalence and incidence of bovine trypanosomosis in an agro-pastoral area of southwestern Burkina Faso

The present study was conducted to determine the prevalence and incidence of trypanosomosis and to investigate some factors influencing them in an agro-pastoral area of southwestern Burkina Faso. A total of 363 crossbred cattle (Baoule-zebu peul), which were bred under natural trypanosomosis challenge, were monitored monthly for parasitaemia, packed cell volume (PCV) and serological analyses over 2 years. The parasitological prevalence estimated at the beginning of the survey using the buffy coat technique (BCT) was 7.54%. As much as 66.7% of all trypanosome infections were due to Trypanosoma vivax, 23.8% due to Trypanosoma congolense and 9.5% due to T. vivax/T. congolense mixed infections. The monthly serological incidence varied from 0.29% to 19.29%.The season was the most important factor influencing the serological prevalence and incidence and the animal PCV. The dry hot season is associated with increasing seroprevalences and incidences and consequently a decreasing average of PCV. In addition, an important spatial heterogeneity was observed.     

Estimation of sensitivity and specificity of two diagnostics tests for bovine immunodeficiency virus using Bayesian techniques

The validation of assays for bovine immunodeficiency virus (BIV) in cattle is hampered by the absence of a gold standard. Two tests that often are used to detect BIV are the indirect fluorescent-antibody assay (IFA) and the nested-set polymerase chain-reaction assay (PCR). IFA detects an antibody response whereas PCR detects the provirus in white blood cells.Using Bayesian techniques performed simultaneously on animals from two different dairy herds, we estimated the performance of the IFA and PCR assays and infection prevalence. Bayesian techniques also were used to derive posterior distributions of sensitivities, specificities, and prevalences. The Bayesian estimates were IFA sensitivity=60%, IFA specificity=88%, PCR sensitivity=80%, PCR specificity=86%, Herd A prevalence=20%, and Herd B prevalence=71%. Although PCR was the more sensitive assay, substantial misclassification of infection would be expected in epidemiological studies of BIV regardless of which assay was used.     

A comparative study on the clinical, parasitological and molecular diagnosis of bovine trypanosomosis in Uganda

The clinical, parasitological and molecular diagnosis of bovine trypanosomosis were compared using samples from 250 zebu cattle exposed to natural trypanosome challenge in Uganda. Clinical examination, molecular and parasitological diagnoses detected 184 (73.6%), 96 (38.4%) and 36 (14.4%) as diseased, respectively. The sensitivity and specificity of clinical examination were 87.5% and 35%, and 78 % and 27 % based on molecular and parasitological diagnoses, as gold standards, respectively. Of the 33, 3, 13 and 12 parasitological-positive cattle that had Trypanosoma brucei, Trypanosoma congolense, Trypanosoma vivax or mixed infections, 78 %, 33 %, 84 % and 100 % respectively manifested clinical signs. Of the 24, 89, 12, 3, 6 and 27 cattle detected by molecular diagnosis to have mixed infections, T. brucei, T. vivax, T. congolense forest-, Savannah- and Tsavo-type, 100%, 83%, 91%, 100%, 67% and 81 % had clinical signs, respectively. In conclusion, treatment of cattle based on clinical examination may clear up to 87.5 % or 78 % of the cases that would be positive by either molecular or parasitological diagnosis, respectively. Under field conditions, in the absence of simple and portable diagnostic tools or access to laboratory facilities, veterinarians could rely on clinical diagnosis to screen and treat cases of bovine trypanosomosis presented by farmers before confirmatory diagnosis in diagnostic centres for few unclear cases is sought.     

A cross-sectional epidemiological survey of bovine trypanosomosis and its vectors in the Savelugu and West Mamprusi districts of northern Ghana

The epidemiology of bovine trypanosomosis was investigated in two districts (Savelugu and West Mamprusi) of Northern Ghana with different land use and environmental characteristics. The land use intensity and environmental change was suspected to be higher in the Savelugu District. A cross-sectional entomological survey conducted along the White Volta river and its tributaries confirmed the presence of only Glossina palpalis gambiensis and G. tachinoides. The challenge index as measured by the product of tsetse density and tsetse infection rate was much higher in the West Mamprusi (19.6) than in the Savelugu district (4.7). A total of 1013 cattle (508 in Savelugu and 505 in West Mamprusi) were bled from a random selection of 16 villages in the Savelugu District and 13 villages in the West Mamprusi District. Blood samples were examined for trypanosomes by the buffy coat technique (BCT). Blood samples that were positive in the BCT or negative in the BCT but with packed cell volume (PCV) values below 21 were further tested with a polymerase chain reaction for trypanosomal DNA. Plasma samples of all cattle were serologically tested with an indirect ELISA for trypanosomal antibodies. The parasitological and serological prevalence of bovine trypanosomoses was significantly higher in West Mamprusi (16 and 53%, respectively) than in Savelugu District (8 and 24%, respectively). An evaluation of animal health at the village herd level, using PCV as an index of anaemia, provided various epidemiological scenarios prevalent in the entire study area.     

PCR identification of Leishmania in diagnosis and control of canine Leishmaniasis

Leishmaniases are endemic in many countries, mainly in rural areas. In Brazil, Leishmania infection is responsible for many cases of Leishmaniases, including recent reports in urban regions. Despite their sensitivity, traditional serological and parasitological methods for detecting Leishmaniases have proven inadequate for species discrimination. This study aimed to identify Leishmania species in biological samples by a fast methodology, avoiding "in vitro" cultivation. Knowledge of the Leishmania species is an important tool in regions where both New World visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL) are prevalent. As these new foci appear in areas not traditionally endemic for VL, the main problem is to distinguish between true autochthonous infections and infections acquired in other well-known endemic areas. Since, domestic dogs are known to be the main VL and CL reservoir, they are regularly investigated in endemic areas to prevent, principally, severe and often fatal VL in humans. However, several infected dogs present no clinical signs or clinical signs similar to other canine diseases. Here, we evaluated the ability of PCR to diagnose VL and distinguish L. (L.) chagasi from other Leishmania species in domestic dogs. Samples from 114 dogs from 30 cities (Sao Paulo, Brazil) were divided into two groups: 44 symptomatic and 70 asymptomatic. They were assayed by parasitological methods (culture and microscopic examination) and PCR to determine L. (L.) chagasi, L. (V.) braziliensis; and in some cases, Leishmania spp. Parasitological tests and PCR-L. chagasi were concordant in 105 samples (92%). VL was confirmed in 49 dogs, while 56 had negative results. Of the 114 samples, 9 had discordant results, but were further tested by PCR-Leishmania spp. with positive results. VL was also confirmed in 4 dogs having negative parasitological tests and positive PCR-L. chagasi. Consequently, this PCR was positive for 100% (53/49) of dogs with parasites detected in parasitological tests. Also, PCR demonstrated high specificity detecting 61 dogs negative for VL. Leishmania infection was negative in 56 dogs, and 5 with positive culture and PCR-Leishmania spp. had CL since they were positive in PCR-L. braziliensis. This study shows the importance of including PCR in diagnosis of Leishmaniases by differential diagnosis contributing to the surveillance and control of VL programs.     

PCV2-DNA in formalin-fixed and paraffin embedded lymph nodes of wild boar (Sus scrofa ssp. scrofa): one sampling approach for two laboratory techniques

Superficial inguinal lymph nodes from 72 wild boars examined in a previous immunohistochemical (IHC) study on porcine circovirus type 2 (PCV2) were selected for a PCV2 polymerase chain reaction (PCR) analysis. Four of these lymph nodes were PCV2-IHC strongly positive with PMWS histological lesions (outcome 1), 6 weak to mild PCV2-IHC positive without PMWS histological lesions (outcome 2) and 62 PCV2-IHC negative. Considering IHC the gold standard for diagnosis, the aims of the study were to evaluate the suitability of the PCV2-DNA extraction from formalin-fixed and paraffin-embedded (FFPE) tissue and the sensitivity and specificity of PCR under two IHC interpretations criteria: (A) the sample was considered positive if the result was outcome 1; (B) the sample was considered positive if the result was outcome 1 or 2. Under (A) criteria, sensitivity and specificity of PCR were 100% and 89.7%, respectively; the Cohen''s Kappa coefficient was 0.49. Under (B) criteria, sensitivity and specificity of PCR were 80.0% and 95.2%, respectively; the Cohen''s Kappa coefficient was 0.72. The high Cohen''s Kappa coefficient under the (B) interpretative criteria indicates good agreement between the two methods. In conclusion, 1) DNA extracted from FFPE specimens of wild boar is suitable for PCR and further represents a screening test for PCV2/PCVD (PCV2 Diseases) investigations in wild boar as well; 2) routine histological sampling can also be useful for PCV2 virological studies in wild boar.     

Field study on nematode resistance in Nelore-breed cattle

The present study evaluated Nelore cattle with different degrees of resistance to natural infections by gastrointestinal nematodes. One hundred weaned male cattle, 11-12 months of age, were kept on the same pasture and evaluated from October 2003 to February 2004. Faecal and blood samples were collected for parasitological, haematological and immunological tests. In February 2004, the 10 most resistant and the 10 most susceptible animals were selected based on individual means of nematode faecal egg counts (FEC). Such animals were slaughtered for worm burden determination and nematode species identification. The repeatability estimates for FEC (+/-S.D.), log-transformed FEC and packed-cell volume (PCV) in all animals were 0.3 (+/-0.05), 0.26 (+/-0.04) and 0.42 (+/-0.05), respectively. The resistant group showed lower FEC and worm burdens than the susceptible group (P<0.05). There were no significant differences between groups regarding mean body weight, weight gain, PCV and total serum protein values (P>0.05). The resistant group showed higher total serum IgE levels (P<0.05) and higher mean eosinophil blood counts. However, the latter was statistically significant only 42 days after the beginning of the study. Nematodes Cooperia punctata and Haemonchus placei were predominant and the correlation between Cooperia and Haemonchus burdens was 0.64 (P<0.05), which indicated that animals presenting increased numbers of one of those genera probably had increased numbers of the other. The current study provides further evidence of IgE active role in nematode immunity and suggests that total serum IgE level might serve as an additional marker to select Nelore cattle that are responsive to H. placei and C. punctata infections.     

副猪嗜血杆菌aroA基因的克隆与序列分析及2种三重PCR检测方法的建立

本试验对分离的5株副猪嗜血杆菌进行了"卫星" 生长试验、生化鉴定和PCR检测。通过对aroA基因序列进行分析,发现这5株菌同标准菌株相比,其核苷酸序列相似性为96.3%~99.8%,氨基酸序列相似性为98.2%~99.5%。此外,还建立了分别针对副猪嗜血杆菌(Hps)、猪伪狂犬病病毒(PRV)、猪细小病毒(PPV)及猪圆环病毒2型(PCV2)、猪细小病毒、猪伪狂犬病病毒的三重PCR检测方法;敏感性试验表明,三重PCR最低能检出Hps、PPV、PRV、PCV2的DNA分别为12、16、7.6和6.3 pg。     

Conditional dependence between tests affects the diagnosis and surveillance of animal diseases

Dependence between the sensitivities or specificities of pairs of tests affects the sensitivity and specificity of tests when used in combination. Compared with values expected if tests are conditionally independent, a positive dependence in test sensitivity reduces the sensitivity of parallel test interpretation and a positive dependence in test specificity reduces the specificity of serial interpretation. We calculate conditional covariances as a measure of dependence between binary tests and show their relationship to kappa (a chance-corrected measure of test agreement). We use published data for toxoplasmosis and brucellosis in swine, and Johne's disease in cattle to illustrate calculation methods and to indicate the likely magnitude of the dependence between serologic tests used for diagnosis and surveillance of animal diseases.