Assessing the Protective Dose of a Candidate DIVA Vaccine against Classical Swine Fever.

Classical swine fever is a highly contagious and deadly disease in swine. The disease can be controlled effectively by vaccination with an attenuated virus known as the "Chinese" (C)-strain. A single vaccination with the C-strain provides complete protection against highly virulent isolates within days after vaccination, making it one of the most efficacious veterinary vaccines ever developed. A disadvantage of the C-strain is that vaccinated animals cannot be serologically differentiated from animals that are infected with wild-type Classical swine fever virus. Previously, a C-strain-based vaccine with a stable deletion in the E2 structural glycoprotein was developed, which allows for differentiation between infected and vaccinated animals (DIVA). The resulting vaccine, which we named C-DIVA, is compatible with a commercial E2 ELISA, modified to render it suitable as a DIVA test. In the present work, three groups of eight piglets were vaccinated with escalating doses of the C-DIVA vaccine and challenged two weeks after vaccination. One group of four unvaccinated piglets served as controls. Piglets were monitored for clinical signs until three weeks after challenge and blood samples were collected to monitor viremia, leukocyte and thrombocyte levels, and antibody responses. The presence of challenge virus RNA in oropharyngeal swabs was investigated to first gain insight into the potential of C-DIVA to prevent shedding. The results demonstrate that a single vaccination with 70 infectious virus particles of C-DIVA protects pigs from the highly virulent Brescia strain.

Experimental Coxiella burnetii infection in non-pregnant goats and the effect of breeding.

Q fever is a zoonosis caused by the intracellular bacterium Coxiella burnetii. In Europe, small ruminants are the main source of human Q fever. Small ruminant herds can be infectious during several lambing seasons. However, it is not clear how infection is maintained in a herd and what role non-pregnant animals play in the transmission of C. burnetii. We therefore inoculated nulliparous goats with C. burnetii, isolated from the outbreak of Q fever in the Netherlands, to gain a better understanding of the role of non-pregnant goats. Seroconversion and excretion of C. burnetii were monitored after inoculation. To study the effect of breeding on the excretion of C. burnetii, the goats were naturally bred and monitored during gestation and after lambing. Our results indicate that C. burnetii infection prior to breeding did not result in infection of the placenta nor did it affect the gestation length or the number of kids born. However, one of the ten does did excrete C. burnetii in the colostrum post-partum and the bacterium was detected in the mammary gland and associated lymph nodes at necropsy. This result indicates that non-pregnant goats might play a role in maintaining Q fever in a goat herd as persistent carriers of infection.

The development of a multiplex serological assay for avian influenza based on Luminex technology.

Avian influenza (AI) is an infectious disease in birds with enormous impact on the poultry sector. AI viruses are divided into different subtypes based on the antigenicity of their surface proteins haemagglutinin (HA) and neuraminidases (NA). In birds, 16 HA subtypes and 9 NA subtypes are detected in different combinations. Traditional serological methods for the subtyping of AI antibodies are labour-intensive and have to be performed for each HA and NA subtype separately. This study describes the development of a multiplex serological assay for subtyping AI antibodies in poultry sera using Luminex xMAP technology. This multiplex assay allows the detection of all AI serotypes in one single assay. For all HA and NA subtypes, recombinant proteins were purified and coupled to colour-coded magnetic bead sets. Using the Luminex MAGPIX device, binding of serum antibodies to the antigens on the bead sets is detected by fluorescent secondary antibodies, and the different bead sets are identified. The results of the multiplex assay were compared with that of the traditional singleplex assays. We show that serotyping using the novel multiplex serological assay is consistent with the results of the traditional assays in 97.8% of the reference sera and in 90.8% of the field sera. The assay has a higher sensitivity than the traditional assays, and requires a smaller sample volume. Therefore, the assay will allow complete AI-serotyping in small volumes of field sera, which will improve the monitoring of AI subtypes circulating in poultry significantly.

Influence of Age and Dose of African Swine Fever Virus Infections on Clinical Outcome and Blood Parameters in Pigs.

African swine fever (ASF) is a fatal disease for domestic pigs, leading to serious economic losses in countries where ASF is endemic. Despite extensive research, efficient vaccines against ASF are lacking. Since peripheral blood cells are important mediators for vaccines, we study the impact of ASF on blood parameters in pigs with different ages and infected with different doses of ASF virus. Four different groups were studied: (1) 12 weeks of age/low virus dose; (2) 12 weeks of age/high virus dose; (3) 18 weeks of age/low virus dose; and (4) 18 weeks of age/high virus dose. By varying in age and/or ASFV inoculation dose, we monitor blood parameters during different degrees of disease. Thirty percent of the pigs survived the infection with a moderately virulent strain of African swine fever virus (ASFV). Animals that did survive infection were generally older, independent from the inoculation dose used. A firm reduction in many different cell types at 3-5 days postinfection (DPI) was accompanied by an increase in body temperature, followed by clinical signs and mortality from day 6 PI. While blood parameters generally normalized in survivors, γδ T cells and IL-10 levels could be related to mortality. These conclusions should be considered in new approaches for protection against ASF.

The effect of C. burnetii infection on the cytokine response of PBMCs from pregnant goats.

In humans, infection with Coxiella burnetii, the causative agent of Q fever, leads to acute or chronic infection, both associated with specific clinical symptoms. In contrast, no symptoms are observed in goats during C. burnetii infection, although infection of the placenta eventually leads to premature delivery, stillbirth and abortion. It is unknown whether these differences in clinical outcome are due to the early immune responses of the goats. Therefore, peripheral blood mononuclear cells (PBMCs) were isolated from pregnant goats. In total, 17 goats were included in the study. Six goats remained naive, while eleven goats were infected with C. burnetii. Toll-like receptor (TLR) and cytokine mRNA expression were measured after in vitro stimulation with heat-killed C. burnetii at different time points (prior infection, day 7, 35 and 56 after infection). In naive goats an increased expression of interleukin (IL)-1ß, tumor necrosis factor (TNF)-α, IL-10 and interferon (IFN)-γ mRNA upon C. burnetii stimulation was detected. In addition, TLR2 expression was strongly up-regulated. In goats infected with C. burnetii, PBMCs re-stimulated in vitro with C. burnetii, expressed significantly more TNF-α mRNA and IFN-γ mRNA compared to naive goats. In contrast, IL-10 mRNA production capacity was down-regulated during C. burnetii infection. Interestingly, at day 7 after inoculation a decreased IFN-γ protein level was observed in stimulated leukocytes in whole blood from infected goats, whereas at other time-points increased production of IFN-γ protein was seen. Our study shows that goats initiate a robust pro-inflammatory immune response against C. burnetii in vitro. Furthermore, PBMCs from C. burnetii infected goats show augmented pro-inflammatory cytokine responses compared to PBMCs from non-infected goats. However, despite this pro-inflammatory response, goats are not capable of clearing the C. burnetii infection.

Contribution of the NS1 gene of H7 avian influenza virus strains to pathogenicity in chickens.

Using reverse genetics (rg), we generated two reassortant viruses carrying the NS1 gene of two closely related HPAIV and LPAIV H7N1 variants (designated rgH7N7 HP(HPNS1) and rgH7N7 HP(LPNS1), respectively) in the backbone of the HP H7N7 strain A/Chicken/Netherlands/621557/03 (rgH7N7 HP). Comparison of these reassortants allowed us to determine the effect of amino acid differences in the nuclear export and nucleolar localization sequences of NS1 on pathogenesis in chickens. Compared to rgH7N7 HP(LPNS1), a delay in weight gain and an increase in mortality were observed for rgH7N7 HP(HPNS1). Furthermore, an increase in viral load in brains, lungs, and cloacal swabs, as well as an increased induction of mRNA for type I interferons and pro-inflammatory cytokines in brains, were observed for rgH7N7 HP(HPNS1). Comparison of rgH7N7 HP(LPNS1) with the backbone strain rgH7N7 HP allowed us to examine differences in pathogenesis due to differences in NS1 alleles. rgH7N7 HP, which contained allele A of NS1 showed a higher in vitro replication rate and proved to be more virulent than the isogenic virus carrying allele B of NS1(rgH7N7 HP(LPNS1)). In addition, higher virus accumulation in the lungs and brains, and an increased induction of host gene responses, especially in the brains, were found for rgH7N7 HP compared to rgH7N7 HP(LPNS1). No large differences were observed in type I interferon expression in the lungs of chickens infected with any of the viruses, suggesting that differences in virulence due to differences in NS1 could be related to differences in the induction of pro-inflammatory cytokines in vital organs such as the brains.

Q fever in pregnant goats: humoral and cellular immune responses.

Q fever is a zoonosis caused by the intracellular bacterium Coxiella burnetii. Both humoral and cellular immunity are important in the host defence against intracellular bacteria. Little is known about the immune response to C. burnetii infections in domestic ruminants even though these species are the major source of Q fever in humans. To investigate the goat's immune response we inoculated groups of pregnant goats via inhalation with a Dutch outbreak isolate of C. burnetii. All animals were successfully infected. Phase 1 and Phase 2 IgM- and IgG-specific antibodies were measured. Cellular immune responses were investigated by interferon-gamma, enzyme-linked immunosorbent spot test (IFN-γ Elispot), lymphocyte proliferation test (LPT) and systemic cytokines. After two weeks post inoculation (wpi), a strong anti-C. burnetii Phase 2 IgM and IgG antibody response was observed while the increase in IgM anti-Phase 1 antibodies was less pronounced. IgG anti-Phase 1 antibodies started to rise at 6 wpi. Cellular immune responses were observed after parturition. Our results demonstrated humoral and cellular immune responses to C. burnetii infection in pregnant goats. Cell-mediated immune responses did not differ enough to distinguish between Coxiella-infected and non-infected pregnant animals, whereas a strong-phase specific antibody response is detected after 2 wpi. This humoral immune response may be useful in the early detection of C. burnetii-infected pregnant goats.

Systemic distribution of different low pathogenic avian influenza (LPAI) viruses in chicken.

BACKGROUND: Since we were able to isolate viable virus from brain and lung of H7N1 low pathogenic avian influenza virus (LPAIV) infected chickens, we here examined the distribution of different LPAIV strains in chickens by measuring the viral AI RNA load in multiple organs. Subtypes of H5 (H5N1, H5N2), H7 (H7N1, H7N7) and H9 (H9N2), of chicken (H5N2, H7N1, H7N7, H9N2), or mallard (H5N1) origin were tested. The actual presence of viable virus was evaluated with virus isolation in organs of H7N7 inoculated chickens. FINDINGS: Viral RNA was found by PCR in lung, brain, intestine, peripheral blood mononuclear cells, heart, liver, kidney and spleen from chickens infected with chicken isolated LPAIV H5N2, H7N1, H7N7 or H9N2. H7N7 virus could be isolated from lung, ileum, heart, liver, kidney and spleen, but not from brain, which was in agreement with the data from the PCR. Infection with mallard isolated H5N1 LPAIV resulted in viral RNA detection in lung and peripheral blood mononuclear cells only. CONCLUSION: We speculate that chicken isolated LPAI viruses are spreading systemically in chicken, independently of the strain.

Chicken dendritic cells are susceptible to highly pathogenic avian influenza viruses which induce strong cytokine responses.

Infection with highly pathogenic avian influenza (HPAI) in birds and mammals is associated with severe pathology and increased mortality. We hypothesize that in contrast to low pathogenicity avian influenza (LPAI) infection, HPAI infection of chicken dendritic cells (DC) induces a cytokine deregulation which may contribute to their highly pathogenic nature. Infection of DC with LPAI H7N1 and H5N2 resulted in viral RNA and NP expression without increase in time, in contrast to HPAI H7N1 and H5N2 mRNA expression. No increase in IFN mRNA was detected after infection with LPAI, but after LPAI H5N2, and not LPAI H7N1, infection the level of bioactive IFNα/ß significantly increased. After HPAI H7N1 and H5N2 infection, significant increases in IL-8, IFN-α, IFN-γ mRNA expression and in TLR1, 3, and 21 mRNA were observed. This enhanced activation of DC after HPAI infection may trigger deregulation of the immune response as seen during HPAI infection in chickens.

Systemic virus distribution and host responses in brain and intestine of chickens infected with low pathogenic or high pathogenic avian influenza virus.

BACKGROUND: Avian influenza virus (AIV) is classified into two pathotypes, low pathogenic (LP) and high pathogenic (HP), based on virulence in chickens.Differences in pathogenicity between HPAIV and LPAIV might eventually be related to specific characteristics of strains, tissue tropism and host responses. METHODS: To study differences in disease development between HPAIV and LPAIV, we examined the first appearance and eventual load of viral RNA in multiple organs as well as host responses in brain and intestine of chickens infected with two closely related H7N1 HPAIV or LPAIV strains. RESULTS: Both H7N1 HPAIV and LPAIV spread systemically in chickens after a combined intranasal/intratracheal inoculation. In brain, large differences in viral RNA load and host gene expression were found between H7N1 HPAIV and LPAIV infected chickens. Chicken embryo brain cell culture studies revealed that both HPAIV and LPAIV could infect cultivated embryonic brain cells, but in accordance with the absence of the necessary proteases, replication of LPAIV was limited. Furthermore, TUNEL assay indicated apoptosis in brain of HPAIV infected chickens only. In intestine, where endoproteases that cleave HA of LPAIV are available, we found minimal differences in the amount of viral RNA and a large overlap in the transcriptional responses between HPAIV and LPAIV infected chickens. Interestingly, brain and ileum differed clearly in the cellular pathways that were regulated upon an AI infection. CONCLUSIONS: Although both H7N1 HPAIV and LPAIV RNA was detected in a broad range of tissues beyond the respiratory and gastrointestinal tract, our observations indicate that differences in pathogenicity and mortality between HPAIV and LPAIV could originate from differences in virus replication and the resulting host responses in vital organs like the brain.

Highly pathogenic or low pathogenic avian influenza virus subtype H7N1 infection in chicken lungs: small differences in general acute responses.

Avian influenza virus can be divided into two groups, highly pathogenic avian influenza virus (HPAI) and low pathogenic avian influenza virus (LPAI) based on their difference in virulence. To investigate if the difference in clinical outcome between LPAI and HPAI in chickens is due to immunological host responses in the lung within the first 24 hours post infection (hpi), chickens were infected with LPAI or HPAI of subtype H7N1. Virus was found in the caudal and cranial part of the lung. With LPAI, virus was localised around the intrapulmonary bronchus and secondary bronchi. In sharp contrast, HPAI was detected throughout the whole lung. However, based on viral RNA levels, no quantitative difference was observed between LPAI and HPAI infected birds. In infected areas of the lungs, an influx of CD8α+ cells as well as KUL01+ macrophages and dendritic cells (DC) occurred as fast as 8 hpi in both infected groups. No major difference between LPAI and HPAI infected birds in the induction of cytokines and interferons at mRNA level in lung tissue was found.In conclusion, the differences in lethality for chickens infected with LPAI or HPAI could be ascribed to difference in location of the virus. However similar amounts of viral RNA, similar cytokine mRNA levels, and similar influxes of CD8α+ and KUL01+ macrophages and DC were found between HPAI and LPAI in the lungs. A cytokine storm at mRNA level as described for mammals was not observed in the lungs of HPAI infected birds within 24 hpi.

The pathogenesis of and susceptibility to malabsorption syndrome in broilers is associated with heterophil influx into the intestinal mucosa and epithelial apoptosis.

Malabsorption syndrome (MAS) in broilers is characterized by enteritis and reduced body weight gain. The pathogenesis of the intestinal lesions and the reasons for susceptibility differences between broiler lines are not clear. We studied the development of enteric lesions, epithelial apoptosis, and cell proliferation in relation to susceptibility. One-day-old chickens from two broiler lines were orally inoculated with intestinal homogenate derived from MAS-affected chickens. Vacuolar degeneration and apoptosis of the villous epithelium and infiltration of heterophils into the lamina propria occurred from day 1 post-inoculation. Following heterophil accumulation, at day 4 to 6 post-inoculation, there was severe apoptosis of the crypt epithelium and villous atrophy. The susceptible broilers had a significantly greater influx of heterophils and, subsequently, severe epithelial apoptosis and cystic damage to the crypts. There appeared to be a causal relationship between heterophil influx and the onset of apoptosis. Coincident with the epithelial apoptosis, MAS-affected chickens had crypt hyperproliferation and faster epithelial turnover. Heterophil infiltration and epithelial apoptosis appear to be critical in the pathogenesis of MAS. Heterophil recruitment may be a major factor in differences in susceptibility to MAS.