Abstract. Bovine mastitis phases induced by Staphylococcus aureus were assessed in 6 lactating cows before challenge and at 1, 4-8, and 9-14 days postinoculation (dpi). Milk lymphocytes, macrophages, and polymorphonuclear cells (PMN) were counted by conventional (manual) cytology, identified by CD3ϩ and CD11bϩ immunofluorescence and counted by flow cytometry (based on leukocyte forward and side light scatter values). Somatic cell counts (SCC) and recovery of bacteria were recorded at the same times. Preinoculation samples showed a lymphocyte-dominated composition. At 1 dpi, the percentage of PMN increased and that of lymphocytes decreased. At 4-8 dpi, PMN were predominant, but the percentage of mononuclear cells increased above that at 1 dpi and further increased by 9-14 dpi (when lymphocytes approached prechallenge values). Based on leukocyte percentages, 3 indices were created from the data: 1) the PMN/lymphocyte percentage ratio (PMN/L), 2) the PMN/macrophage percentage ratio (PMN/M), and 3) the phagocyte (PMN and macrophage)/ lymphocyte percentage ratio (Phago/L). Significant correlations were found between cytologic and flow cytometric data in all of these indicators (all with P Յ 0.01). These indices identified nonmastitic, early inflammatory (1-8 dpi), and late inflammatory (9-14 dpi) animals. In contrast, SCC and bacteriology did not. Although sensitivity of the SCC was similar to that of Phago/L, the specificity of SCC was almost half that of the Phago/ L index. Based on flow cytometry indicators, an algorithm for presumptive diagnosis of bovine mastitis was developed. Flow cytometry provides results as valid as those obtained by conventional (manual) cytology, shows greater ability to identify mastitic cases than does SCC, and may identify 3 mammary gland healthrelated conditions.Infectious bovine mastitis is a major health problem of dairy cattle that results in decreased milk production and decreased milk quality. Staphylococcus aureus is a major bacterial pathogen associated with this disease. 18 Identification of bovine mastitis has historically been based on counting of all cells present in milk (leukocytes and epithelial cells), i.e., somatic cell counts (SCC). Counts Ͼ500,000 cells/ml are usually associated with bovine mastitis, which results in reduced milk production and reduced shelf life of dairy products. 8,32 The reduction of bovine mastitis prevalence is a major goal of the dairy industry throughout the world. To achieve this goal, most countries ban from the market milk with SCC Ͼ 500,000 cells/ml or charge fees for milk deliveries that approach that figure (Booth JM: 1996, Annu Meet Natl Mastitis Counc).In spite of these policies, it is questionable whether measures based on lower SCC will result in decreased prevalence of bovine mastitis. Although high SCC (Ͼ1 ϫ 10 6 cells/ml) is regarded as an accurate indicator of bovine mastitis, both mastitic and healthy cows can yield SCC below that figure. 25 Low SCC may also be associated with milk of poor industrial value. 8 The SCC is a quanti...

a b s t r a c tWe conducted a matched case-control study to evaluate risk factors for infection with highly pathogenic avian influenza (HPAI) H5N1 virus in poultry farms during the epidemic of 2006-2007 in Nigeria. Epidemiologic data were collected through the use of a questionnaire from 32 case farms and 83 control farms. The frequency of investigated exposure factors was compared between case and control farms by using conditional logistic regression analysis. In the multivariable analysis, the variables for (i) receiving visitors on farm premises (odds ratio [OR] = 8.32; 95% confidence interval [CI] = 1.87, 36.97; P < 0.01), (ii) purchased live poultry/products (OR = 11.91; 95% CI = 3.11-45.59; P < 0.01), and (iii) farm workers live outside the premises (OR = 8.98; 95% CI = 1.97, 40.77; P < 0.01) were identified as risk factors for HPAI in poultry farms. Improving farm hygiene and biosecurity should help reduce the risk for influenza (H5N1) infection in poultry farms in Nigeria.

SUMMARYThe daily progression of the 2006 (January-June) Nigerian avian influenza (AI H5N1) epidemic was assessed in relation to both spatial variables and the generation interval of the invading virus. Proximity to the highway network appeared to promote epidemic dispersal : from the first AI generation interval onwards >20 % of all cases were located at <5 km from the nearest major road. Fifty-seven per cent of all cases were located f31 km from three highway intersections. Findings suggest that the spatial features of emerging infections could be key in their control. When the spatial location of a transmission factor is well known, such as that of the highway network, and a substantial percentage of cases (e.g. >20 %) are near that factor, early interventions focusing on transmission factors, such as road blocks that prevent poultry trade, may be more efficacious than interventions applied only to the susceptible population.

The effect of infection by various strains of Marek's disease virus (MDV) on the immune function of 3-week-old chickens was examined. MDV strains of low (CU-2, RB-7) and high (RB-3, MD-5, and MD-11) pathogenicity were compared with prototype JM-10 strain of moderate pathogenicity. Mortality, whole body weight, relative weights of lymphoid organs, histopathology, humoral antibody responses to thymus-dependent and -independent antigens, and in vitro lymphocyte responses to mitogen stimulation were investigated at 1, 2, and 3 weeks postinfection. MDV strains of high pathogenicity significantly depressed responses at 3 weeks postinfection, seeming to indicate the ability of these viruses to induce severe immunodepression. However, the fact that the moderately pathogenic and even some of the low-pathogenicity strains induced immunodepression suggests that other viral mechanisms are also important in its determination.