P.N. Nyaga

Pathogenesis of bovine herpesvirus-1 (BHV-1) infections: interactions of the virus with peripheral bovine blood cellular components.

Abstract Bovine herpesvirus -1 (BHV-1) is believed to reach the placenta via the hematogenous route as the virus has been recovered from the blood buffy coat cells of experimentally infected cattle. However, the manner in which the virus relates to these and other blood cells while in transit in the blood is not known. The nature of this relationship was investigated in the present study. An in vitro correlate of the in vivo cell-virus interactions was simulated by isolating peripheral blood cells on a Ficoll-Hypaque gradient and testing their capacity to adsorb and act as host cells for BHV-1 replication. It was shown that all leukocytes, but not red cells, can adsorb virus readily. Of the leukocytic fraction, monocytes and lymphocytes adsorb the virus most effectively. Monocytes supported viral replication while lymphocytes could do so only after stimulation with phytohemagglutinin. It is concluded that in vivo replicating BHV-1 is transported in monocytes, and is adsorbed to all leukocytes from which it finally reaches the placenta, leading to abortion.

Specific Detection of Pasteurella multocida in Chickens with Fowl Cholera and in Pig Lung Tissues Using Fluorescent rRNA In Situ Hybridization

ABSTRACT A Pasteurella multocida species-specific oligonucleotide probe, pmhyb449, targeting 16S rRNA was designed and evaluated by whole-cell hybridization against 22 selected reference strains in animal tissues. It differentiated P. multocida from other bacterial species of the familiesPasteurellaceae and Enterobacteriaceaeand also from divergent species of the orderCytophagales (except biovar 2 strains ofPasteurella avium and Pasteurella canis,which have high 16S rRNA similarity to P. multocida). The potential of the probe for specific identification and differentiation of P. multocida was further detected in formalin-fixed paraffin-embedded lung tissues from experimental fowl cholera in chickens and infections in pigs. In chicken lung tissuesP. multocida cells were detected singly, in pairs, as microcolonies, and as massive colonies within air capillaries (septa and lumen), parabronchial septa, and blood vessels (wall and lumen). In pig lung, postmortem-injected P. multocida was detected in the alveoli (lumen and wall), and in both animals the bacterial cells were seen in the bronchi. The results showed that with the oligonucleotide probe pmhyb449, fluorescent in situ hybridization is a suitable and fast method for specific detection of P. multocida in histological formalin-fixed tissues. The test was replicable and reproducible and is recommended as a supplementary test for diagnosis and as a tool in pathogenesis studies of fowl cholera and respiratory tract infections in pigs due to P. multocida.

Haemorrhagic pancarditis in cattle infected with Trypanosoma vivax.

Haemorrhagic pancarditis has been studied microscopically and ultrastructurally. Haemorrhages, oedema, mononuclear cell infiltration, degeneration, fragmentation, atrophy and lysis of myofibres, and extravascular localisation of the parasite were observed.

Epidemiology of equine influenza, risk by age, breed and sex

Abstract Three hundred and sixty cases of diagnosed equine influenza reported to the Veterinary Medical Data Program (VMDP) of the National Cancer Institute, U.S.A., were tested for the independent effects of age, breed and sex, relative to a reference clinic-hospital population of 84,562 equine patients. Horses of age category 2–6 months showed a significant risk above unity for infection with equine influenza virus whereas, horses in age category 7–10 yr showed a significant, low and sparing risk. Horses under two months or over 10 years, as well as those in ages from 6 months to 7 yr had non-significant low risks. The quarter horse breed showed a significant risk above unity whereas the thoroughbred showed a significant risk below unity. All other breeds of horses had non-significant low risks. Sex did not contribute significantly to the epidemiology of the infection since there were no significant risk differences between sexes. A re-infection rate of 0.05 for cases pooled for age, breed and sex was identified.

Effect of Immunosuppression on Newcastle Disease Virus Persistence in Ducks with Different Immune Status

This study was carried out to verify the possibility that ducks are sources of Newcastle disease (ND) virus infection for chickens in mixed flocks. Immunosuppressed (IS) and non immunosuppressed (NIS) birds, at three different antibody levels (medium, low and absent) were used; the titres having been induced through vaccination, and Immunosuppression done using dexamethazone. Each of the 3 respective groups was further divided into 2 groups of about 12 ducks each: one challenged with velogenic ND virus; the other not challenged. Selected ducks from all groups had their antibody titres monitored serially using hemagglutination inhibition test, while two birds from each of the challenged groups were killed and respective tissues processed for ND viral recovery, using chicken embryo fibroblasts. In general, antibody titres of IS and NIS challenged ducks were significantly higher than their unchallenged counterparts (P < 0.05). Non-challenged pre-immunised ducks had a progressive decrease in antibody levels; non-immunised ducks did not seroconvert. Newcastle disease virus was isolated from livers and kidneys of the challenged ducks throughout the experimental period; indicating a possibility of viral excretion, especially when the birds are stressed. It, therefore, provides another possible model of viral circulation within mixed flocks.

Market fish hygiene in Kenya

Vibrio parahaemolyticus was isolated from 53 out of 584 samples (9.1%) of market fish. All strains were Kanagawa negative and were distributed as follows: sea fish 5 out of 370 samples (1.4%), shellfish 48 out of 214 samles (22.4%). Other fish spoilage microflora recovered were: Alcaligenes faecalis, Pseudomonas aeruginosa, Proteus vulgaris, Aeromonas spp. and Vibrio alginolyticus. Total aerobic counts and coliform counts per gram for the lake fish ranged from 2.6 X 10(2) to 6.6 X 10(7) and 10 to 1.0 X 10(2), respectively. Those from marine fish ranged from 1.0 X 10(5) to 8.8 X 10(6) and 2.0 X 10(3) to 1.6 X 10(4), respectively. Counts for marine fish gills alone ranged from 1.4 X 10(5) to 3.4 X 10(8) and 7.2 X 10(2) to 1.4 X 10(7), respectively. No high-temperature (44 degrees) coliforms were recovered from either lake or marine samples.

Time-course investigation of infection with a low virulent Pasteurella multocida strain in normal and immune-suppressed 12-week-old free-range chickens

Twelve-week-old indigenous chickens, either immune-suppressed using dexamethasone (IS) or non-immune-suppressed (NIS), were challenged with a low virulent strain, Pasteurella multocida strain NCTC 10322T, and developed clinical signs and pathological lesions typical of chronic fowl cholera. NIS birds demonstrated much more severe signs of fowl cholera than IS birds. With few exceptions, signs recorded in IS and NIS birds were of the same types, but significantly milder in the IS birds, indicating that immune suppression does not change the course of infection but rather the severity of signs in fowl cholera. P. multocida signals by fluorescent in situ hybridization (FISH) were observed between 1 h and 14 days in the lungs, trachea, air sacs, liver, spleen, bursa of Fabricius and caecal tonsils, while signals from other organs mostly were observed after 24 h. More organs had FISH signals in NIS birds than in IS birds and at higher frequency per organ. Many organs were positive by FISH even 14 days post infection, and it is suggested that these organs may be likely places for long-term carriage of P. multocida following infection. The present study has demonstrated the spread of P. multocida in different tissues in chickens and distribution of lesions associated with chronic fowl cholera, and pointed to a decrease of pathology in IS birds. Since dexamethasone mostly affects heterophils, the study suggests that these cells play a role in the development of lesions associated with chronic fowl cholera in chickens.

Occurrence of atypical fowlpox in poultry farms in Kenya.

Atypical fowlpox occurred in several poultry farms in Kenya. On two occasions layers had their eyes closed and egg production dropped. Fowlpox virus was isolated from lesions on the inner surfaces of the closed eyelids. Other chickens had lesions covered by yellow caseous necrotic material in the mouth, around the epiglottis, and in the trachea and choanae. Typical proliferative cutaneous lesions were observed in birds of all ages in other flocks examined. Fowlpox virus was recovered from both cutaneous and diphtheritic lesions. The infected chorioallantoic membranes had focal hyperplastic lesions containing pink-staining intracytoplasmic inclusion bodies in most cells. Transmission studies showed that the virus was highly virulent to susceptible chickens.

The comparative antigenic characterization of Newcastle disease virus strains isolated in Kenya and Kazakhstan.

Twenty six Newcastle disease viruses--12 reference strains and 14 strains isolated in Kenya and Kazakhstan--were characterized by means of a large panel of 38 monoclonal antibodies (MAB) directed against all the three envelope proteins: matrix, hemagglutinin-neuraminidase and fusion. The essential distinctions were revealed between the viruses isolated in Kenya and Kazakhstan while the differences amongst the viruses belonging to the same local group were much smaller. The heterogeneity amongst the viruses isolated in Kenya was more expressed as compared to the Kazakhstanian strains.

Isolation of Infectious Bursal Disease Virus Using Indigenous Chicken Embryos in Kenya.

Infectious bursal disease virus (IBDV) isolates were recovered from outbreaks to initiate activities towards developing a local vaccine strain. Use of indigenous chicken embryos was exploited to determine their potential, promote utilization of local resources for research, and enhance household economic activities. Bursa of Fabricius (BFs) samples from outbreaks shown to be IBDV positive was homogenized and inoculated in 4-week-old specific pathogen-free (SPF) IBDV seronegative white leghorn chicks. The harvested virus was inoculated into 11-day-old indigenous chicken embryos that were IBDV seronegative and passaged serially three times after which they were inoculated into 4-week-old indigenous chicks to test for presence and virulence of propagated virus. Out of 153 BFs collected from outbreaks, 43.8% (67/153) were positive for IBDV antigen and 65.7% (44/67) caused disease in SPF chicks. The embryo mean mortalities were 88% on primary inoculation, 94% in 1st passage, 91% in 2nd passage, and 67% in 3rd passage. After the third passage in embryos all the 44 isolates were virulent in 4-week-old indigenous chicks. The results show that indigenous chicken embryos support growth of IBDV and can be used to propagate the virus as an alternative viral propagating tool for respective vaccine preparation.