Duration of immunity in dogs vaccinated against leptospirosis with a bivalent inactivated vaccine

Duration of immunity in dogs induced with current commercial inactivated leptospirosis vaccines and evaluated against experimental infection, to date, has hardly been documented. The purpose of the present work was to assess the duration of immunity in dogs that is attainable with a commercial inactivated bivalent leptospirosis vaccine. For this purpose, young dogs were vaccinated twice followed by challenge with either Leptospira interrogans serovar canicola or L. interrogans serovar icterohaemorrhagiae 5 weeks, 27 weeks or 56 weeks after the second vaccination. For assessment of the duration of immunity, titres of agglutinating serum antibodies were measured before and after challenge, and the effects of challenge on a variety of parameters were determined including reisolation of challenge organisms from blood, urine and kidney. Both challenge strains induced a generalised infection in control dogs, the canicola strain being most virulent. From the results with different parameters it appeared that the two vaccinations induced a high rate of protection from generalised infection with canicola and icterohaemorrhagiae at 5, 27 and 56 weeks after the second vaccination. In addition, after 56 weeks, still a high level of immunity against renal infection with sv. canicola and, as a consequence, urinary shedding of sv. canicola bacteria, was demonstrated. It was, therefore, concluded that with this vaccine, using this vaccination schedule, a duration of immunity of 1 year can be attained against infection with both serovars.     

Duration of immunity in foxes vaccinated orally with ERA vaccine in a bait.

Red foxes (Vulpes vulpes) vaccinated orally with the ERA strain of rabies vaccine in a bait were challenged after 83 mo. Ten of 11 foxes that had seroconverted following vaccination resisted challenge with a virulent rabies virus which produced clinical signs of rabies in 6 of 6 unvaccinated foxes. Five of 11 vaccinated animals retained titers of rabies virus neutralizing antibody throughout the period. Although 6 of 11 had no detectable antibody at the time of challenge, 5 of these 6 resisted challenge and had an anamnestic response, as indicated by elevated titers of antibody when measured at day 77 postchallenge. These results show that foxes can be immunized successfully with a single oral dose of ERA vaccine, probably with protection against a lethal rabies challenge, for at least 7 y.     

Pneumonia of turkey breeder hens associated with Mycoplasma synoviae

Turkey breeder hens showed an increase in mortality beginning at 38 wk of age with no other clinical signs or changes in egg production. While no respiratory signs were observed in live turkeys, those that died consistently had gross lesions of pneumonia. Histopathology of lungs revealed serofibrinous bronchopneumonia, lymphofollicular reaction, and other features suggesting a bacterial etiology. However, except for incidental findings, bacteria were not visualized in the sections examined, and none were isolated in meaningful numbers on routine bacteriologic media. At 42 wk of age the flock showed serologic evidence of infection with Mycoplasma synoviae (MS), and MS was identified by both mycoplasma culture and polymerase chain reaction (PCR) procedures in samples from choanal clefts and tracheas. Results of lung histopathology and PCR tests were consistent with a diagnosis of pneumonia caused by MS.     

Isolation from turkey breeder hens of a reassortant H1N2 influenza virus with swine, human, and avian lineage genes

Type A influenza viruses can infect a wide range of birds and mammals, but influenza in a particular species is usually considered to be species specific. However, infection of turkeys with swine H1N1 viruses has been documented on several occasions. This report documents the isolation of an H1N2 influenza virus from a turkey breeder flock with a sudden drop in egg production. Sequence analysis of the virus showed that it was a complex reassortant virus with a mix of swine-, human-, and avian-origin influenza genes. A swine influenza virus with a similar gene complement was recently reported from pigs in Indiana. Isolation and identification of the virus required the use of nonconventional diagnostic procedures. The virus was isolated in embryonated chicken eggs by the yolk sac route of inoculation rather than by the typical chorioallantoic sac route. Interpretation of hemagglutination-inhibition test results required the use of turkey rather than chicken red blood cells, and identification of the neuraminidase subtype required the use of alternative reference sera in the neuraminidase-inhibition test. This report provides additional evidence that influenza viruses can cross species and cause a disease outbreak, and diagnosticians must be aware that the variability of influenza viruses can complicate the isolation and characterization of new isolates.     

A novel delivery of oxytetracycline in turkey breeder hens.

A novel product (SQ12) for subcutaneous (SQ) injectable delivery of oxytetracycline (OTC) has been developed for use in livestock. SQ12 employs microfluidic spheres encasing OTC crystals, which allows for longer release of the OTC compared with other injectable antibiotics. The objectives of the study were to determine serum and tissue levels of SQ12 in turkey breeder hens to 14 days postinjection and to evaluate effects of SQ12 on reproductive status. Thirty photostimulated hens were housed in litter floor pens and provided with 14.5 hr of light per day in a curtain-sided facility. Six hens served as untreated controls. Twelve hens per treatment group received SQ injections in the neck with SQ12 at 11.4 (L dose group) or 22.7 mg/kg (H dose group) to assess low and high doses, respectively. Serum samples were obtained from each hen at predose and 6, 12, 24, 48, 72, 96, 168, 240, and 336 hr postinjection. All hens were euthanatized at 14 and 15 days postinjection. One-half of the hens in each treatment group were sampled (liver, lung, kidneys, and breast muscle) for tissue residue levels of OTC. The control group had no detectable OTC in serum or tissues at any sample collection time. There were no detectable serum levels of OTC in either treatment group prior to injection. The average serum concentrations of the L and H dose groups showed similar depletion curves although the H dose group was 42% higher at maximum concentration than the L group. Average tissue concentration of OTC for all tissues sampled from the H dose group was twice that of the L dose group. All tissue levels were below the OTC residue tolerance limit. SQ12 provided an extended source of OTC in serum of turkey breeder hens with no effect on reproductive status. SQ12 may provide for a novel treatment of bacterial infection in turkey breeder hens with longer lasting serum levels compared with other single injectable OTC products.     

Three-year duration of immunity in dogs vaccinated with a canarypox-vectored recombinant canine distemper virus vaccine

Two studies evaluated the duration of serologic response to the recombinant, canarypox-vectored canine distemper virus vaccine (Recombitek, Merial). Serologic duration of immunity was shown to be at least 36 months. Thus, Recombitek provides protection when administered less frequently than the manufacturer's label. After the initial vaccination protocol of two or more doses administered approximately 4 weeks apart, with the last dose given at 12 to 16 weeks of age or older, and re-vaccination at 1 year of age, Recombitek can confidently be readministered every 3 years with assurance of protection in immunocompetent dogs. This allows the vaccine to be administered in accordance with the recommendations of the American Animal Hospital Association Canine Vaccine Task Force and others.     

Vaccination of turkey breeder hens and toms for fowl cholera with CU strain

Unvaccinated laying breeder hens and semen-producing toms were susceptible to the CU strain of Pasteurella multocida and highly susceptible to a virulent strain of P. multocida. Laying breeders vaccinated with CU strain when environmental temperatures were low ceased egg production during the first week after vaccination and had 29% mortality, whereas those vaccinated when temperatures were moderate had only a 25% decrease in egg production and 17% mortality. Comparable nonlaying breeders vaccinated during moderate temperatures did not die. Although few semen-producing toms died postvaccination and the quantity and quality of semen was not affected, 21.7% developed torticollis. Laying breeders were protected against CU vaccine and challenge with virulent P. multocida if vaccinated every 4 weeks beginning when 7 weeks old. Potential breeders vaccinated before laying with combinations of 3 vaccinations via drinking water, wing-web puncture, or inoculation into the air spaces of the head through the auditory tube were protected against challenge after the onset of laying. However, vaccination via wing-web puncture at 25 weeks of age resulted in abscesses that failed to resolve. The combination of vaccinations most effective in protecting laying breeders was vaccination in the drinking water at 7 and 11 weeks and inoculation into the air spaces of the head at 15 weeks.     

Fractionation of neutralising antibodies in serum of ducklings vaccinated with live duck hepatitis virus vaccine

Neutralising antibodies were present in duckling serum four days after vaccination of two-day-old ducklings with live duck hepatitis virus vaccines. The antibodies were found in the macroglobulin and 7S fractions by Sephadex G200 chromatography, had gamma or beta 2 mobility in immunoelectrophoresis and reacted with an antiserum to duck immunoglobulins.     

Degenerative myopathy in turkey breeder hens: a comparative study of normal and affected muscle

The pH of affected tissue within the green lesion characteristic of degenerative myopathy in the supracoracoideus muscle of turkey breeder hens was 7.4 to 7.8 and there was a high concentration of albumin. Histological examination showed that the striations of affected muscle fibres were more pronounced and curved than those of normal fibres. Examination of the affected fibres using the electron microscope showed that the curvature resulted from displacement of groups of myofibrils. The ultrastructure of these myofibrils differed markedly from that of normal muscle. The A‐band was granular and ill‐defined, while extensive degradation of the I‐band and Z‐line was observed. In addition, the sarcoplasmic reticulum was extensively disrupted and mitochondria had degenerated.     

Persistence of immunity in commercial egg-laying hens following vaccination with a killed H6N2 avian influenza vaccine

The California poultry industry experienced an outbreak of H6N2 avian influenza beginning in February 2000. The initial infections were detected in three commercial egg-laying flocks and a single noncommercial backyard flock but later spread to new premises. The vaccination of pullet flocks with a commercially prepared, killed autogenous vaccine prior to their placements on farms with infected or previously infected flocks was used as a part of the eradication programs for some multiage, commercial egg production farms. The purpose of this study was to follow three vaccinated flocks on two commercial farms to track the immune responses to vaccination. The antibody-mediated responses of the three flocks followed in this study were markedly different. One flock achieved 100% seroconversion at 12.5 wk of age, but by 32 wk of age, all of the hens were seronegative by agar gel immunodiffusion (AGID). In contrast, at 32 wk of age, flocks from the other farm (flocks 2A and 2B) were 95% and 72% seropositive by AGID, respectively. Of the differences that were identified between the vaccination protocols on the two farms, the distinction that could explain the level of disparity between responses is the delivery of the second dose of vaccine with a bacterin on the first farm, which may have interfered with the persistence of immunity in this flock. Hens from flocks 2A and 2B were experimentally challenged at 25 wk of age with H6N2 avian influenza virus. Hens from flock 2A did not transmit virus to naive contact-exposed hens, but hens from flock 2B did. At 34 wk of age, hens from flock 2A were again challenged and naive contact-exposed hens were infected in this second trial. These challenge experiments served to demonstrate that despite detectable antibody responses in flocks 2A and 2B, the birds were protected from infection for less than 21 wk after the second vaccination.     

Effects of live attenuated and killed Salmonella vaccine on T-lymphocyte mediated immunity in laying hens

The impact of live and killed Salmonella vaccines on cell-mediated immunity (CMI) was investigated in 18- and 32-week-old White Leghorn chickens, by assessing splenic lymphocyte proliferation, expression of IL-2 mRNA in concanavalin A (Con A) stimulated cells and flow cytometric analysis of cell subpopulations. Con A and Salmonella enteritidis (SE) flagella induced proliferation of splenocytes were enhanced in the 18- and 32-week-old chickens treated with live vaccine, compared to the corresponding control chickens. Among the killed vaccine treated birds, Con A-mediated response was higher in the 18-week-old chickens compared to the corresponding control birds. Increased proliferation was accompanied by increased CD4 and reduced CD8 and gammadelta T-lymphocytes in the 18-week-old live vaccine treated chickens. Relative expression of IL-2 mRNA in Con A-stimulated splenocytes from 18-week-old birds was not affected by vaccine treatment. Overall, live vaccine was more effective in increasing the lymphocyte proliferation to Con A as well as SE antigen. This enhanced CMI may prove beneficial in protecting chickens against SE infection.     

Effect of a live reovirus vaccine on reproductive performance of broiler breeder hens and development of viral tenosynovitis in progeny.

A live commercial reovirus vaccine, Enterovax, was administered to adult broiler breeder hens via the drinking water to determine its efficacy in stimulation of circulating antibody. This vaccine was compared with a commercial inactivated reovirus vaccine. Only the inactivated product resulted in increased antibody as measured by a commercial enzyme-linked immunosorbent assay. However, the live reovirus vaccine caused diarrhea in the hens and decreased eggshell quality, fertility, and hatchability. In addition, the live vaccine virus was vertically transmitted from hens to their progeny, resulting in increased embryonic mortality and viral tenosynovitis.     

Responses of chickens vaccinated with a live attenuated multi-valent ionophore-tolerant Eimeria vaccine

Coccidiosis, caused by Eimeria species, is a serious economic disease of chickens (Gallus gallus) and the search for vaccines to control the disease is intensifying especially with the increasing threat of drug resistance. A live attenuated multi-valent ionophore-tolerant Eimeria vaccine has been developed that contains three ionophore-resistant Eimeria species, E. tenella, E. maxima and E. acervulina. The attenuated lines were derived from virulent field strains resistant to monensin ionophore by selection for early development in chicks. The vaccine was administered by gavage and through drinking water to broiler chickens, Chinese Yellow strain, reared in wire cages. Vaccinated medicated birds performed better than vaccinated unmedicated and medicated unvaccinated groups. The final mean weights of vaccinated medicated birds were significantly higher (P<0.05), and a better vaccine protection index, using both vaccinating methods, was achieved. Results indicated that concomitant use of ionophores and vaccines could be a useful adjunct to planned immunization in the control of coccidiosis.     

Duration of immunity engendered by a single dose of a cold-adapted strain of Avian pneumovirus

The duration of immunity after a single dose of a cold-adapted strain of Avian pneumovirus (APV) was studied. Turkeys were vaccinated at 1 wk of age and challenged with virulent virus 3, 7, 10, and 14 wk later. Nonvaccinated groups were also challenged at the same times. No clinical signs were observed in the vaccinated birds after vaccination or after any challenge. No viral RNA was shed by the vaccinated birds after any challenge. The nonvaccinated birds shed viral RNA after all challenges. Avian pneumovirus-specific humoral antibodies were detected in the vaccinated birds until 14 wk after vaccination. The results of this preliminary study indicate that inoculation with a single dose of a cold-adapted strain of APV at 1 wk of age provides protection until 15 wk of age.