Subclinically Infected Research Articles

A survey to detect subclinical polyomavirus infections of captive psittacine birds in Germany

Infections of avian polyomavirus (APV) are known to cause fatal disease in a wide range of psittacine and non-psittacine birds. Here, we present a survey to investigate the existence of subpopulation of persistent or subclinically infected parrots inside the population of captive psittacine birds in Germany. DNA was isolated from feathers of 85 symptom-free birds from 20 different genera (all psittaciformes) taken from 30 different breeders from all over Germany. The presence of APV was analysed by performing polymerase chain reaction assays (PCR). APV was detected in none of the samples, indicating that the existence of a subpopulation of captive psittacine birds having a persistent APV infection in Germany seems to be relatively low.

Development and Evaluation of an Enzyme-Linked Immunosorbent Assay for Quantifying Antibodies to Japanese Encephalitis Virus Nonstructural 1 Protein To Detect Subclinical Infections in Vaccinated Horses

Antibodies to Japanese encephalitis virus (JEV) nonstructural 1 (NS1) protein constitute a marker of natural JEV infection among populations vaccinated with inactivated JE vaccine. In Japan, with few recent human JE cases, the natural infection rate is critical to evaluate the necessity of continuing JE vaccination. A sensitive immunochemical staining method for detecting NS1 antibodies in individuals naturally and subclinically infected with JEV was previously established. Here, an enzyme-linked immunosorbent assay (ELISA) to detect NS1 antibodies in equine sera was developed and evaluated as an alternative to immunostaining. By this method, NS1 antigens contained in culture fluids from cells stably transfected with the NS1 and NS2A genes were captured by a rabbit anti-NS1 polyclonal antibody. Three nanograms per well of NS1 antigen, corresponding to 1:2 to 1:8 dilutions of the culture fluid, was sufficient for testing. ELISA values were obtained by a single-serum dilution (1:100), which correlated with ELISA titers obtained by an endpoint method. Under a tentative cutoff value (0.122) statistically calculated from NS1 antibody levels of horses in an area where JEV is not endemic, a high level of qualitative agreement (85.3%) was obtained between the ELISA and immunostaining methods. A significant correlation coefficient (0.799; P < 0.001) was also obtained between the two methods. Three experimentally infected horses seroconverted no later than 13 to 23 days postinfection, whereas 4 field horses infected during an epizootic remained positive for NS1 antibodies for at least 40 weeks. Our results indicate that the ELISA used here was sufficiently sensitive to detect subclinical infections in vaccinated equine populations.

Cell-mediated immune responses in healthy children with a history of subclinical infection with Japanese encephalitis virus: analysis of CD4+ and CD8+ T cell target specificities by intracellular delivery of viral proteins using the human immunodeficiency virus Tat protein transduction domain.

Japanese encephalitis virus (JEV), a single-stranded positive-sense RNA virus of the family Flaviviridae, is the major cause of paediatric encephalitis in Asia. The high incidence of subclinical infections in Japanese encephalitis-endemic areas and subsequent evasion of encephalitis points to the development of immune responses against JEV. Humoral responses play a central role in protection against JEV; however, cell-mediated immune responses contributing to this end are not fully understood. The structural envelope (E) protein, the major inducer of neutralizing antibodies, is a poor target for T cells in natural JEV infections. The extent to which JEV non-structural proteins are targeted by T cells in subclinically infected healthy children would help to elucidate the role of cell-mediated immunity in protection against JEV as well as other flaviviral infections. The property of the Tat peptide of Human immunodeficiency virus to transduce proteins across cell membranes, facilitating intracellular protein delivery following exogenous addition to cultured cells, prompted us to express the four largest proteins of JEV, comprising 71 % of the JEV genome coding sequence, as Tat fusions for enumerating the frequencies of virus-specific CD4(+) and CD8(+) T cells in JEV-immune donors. At least two epitopes recognized by distinct HLA alleles were found on each of the non-structural proteins, with dominant antiviral Th1 T cell responses to the NS3 protein in nearly 96 % of the cohort. The data presented here show that non-structural proteins are frequently targeted by T cells in natural JEV infections and may be efficacious supplements for the predominantly antibody-eliciting E-based JEV vaccines.

Unapparent foot and mouth disease infection (sub-clinical infections and carriers): implications for control.

Unlike animals which are carriers of foot and mouth disease (FMD), sub-clinically infected animals may be highly contagious. The implications of sub-clinical infections for the control of FMD are serious because such animals are likely to disseminate the disease when in contact with susceptible livestock. Recent dissemination of FMD virus (FMDV) in Europe shows that sub-clinically infected animals render trade in animals or animal products a potential risk for importing countries. This clearly demonstrates that the paradigm 'free of FMD without vaccination' is not synonymous with 'risk-free'. The risk of introduction of subclinical FMD into FMD-free countries may increase significantly, with the occurrence of large susceptible animal populations, changed agricultural practices, expansion of trade in live animals and animal movements, increased trade in animal products and greater mobility of people. Such changes in circumstances require that national and international authorities remain continuously vigilant to determine any altered risk for importation of FMD. A few historical reports and some recent observations in southern Africa indicate the possibility of dissemination of FMD by bovine carriers into herds of susceptible cattle. These reports have greatly influenced FMD trade policies and thus, FMD control and eradication strategies. However, other field evidence does not support this claim and several controlled experiments were unable to show that carriers are able to initiate disease. When millions of cattle were systematically vaccinated with good quality vaccines, FMD disappeared in spite of a large sentinel population in the form of calves and unvaccinated sheep and pigs. A low number of carriers most likely persisted, but they did not hamper the eradication of the disease. Vaccination policies and trade regulation must be based on risk assessments taking these factors into consideration.

Babesia gibsoni infection among dogs in the southeastern United States.

To identify subclinical Babesia gibsoni infection in American Pit Bull Terriers from the southeastern United States and to determine the genetic sequence of parasite DNA isolated from these dogs. Case series. 33 American Pit Bull Terriers and 87 dogs of various other breeds. Blood smears were examined for microscopic evidence of the parasite, and DNA was extracted from blood samples and used in a polymerase chain reaction (PCR) assay designed to amplify the small subunit ribosomal RNA gene sequence of B. gibsoni. Amplification products of the expected size were sequenced, and sequences were compared with published sequences for B. gibsoni isolates. Hematocrit, platelet count, mean platelet volume, WBC count, and eosinophil count were compared between dogs with positive PCR assay results and dogs with negative results. Results of the PCR assay were positive for 18 of the 33 (55%) American Pit Bull Terriers, including all 10 dogs with microscopic evidence of parasitemia. Only 1 of these dogs was clinically ill at the time blood samples were collected. Results of microscopic evaluation of blood smears and of the PCR assay were negative for the 87 other dogs. Hematocrit and platelet count were significantly lower in dogs with positive PCR assay results than in dogs with negative results. Results suggest that American Pit Bull Terriers in the southeastern United States may be subclinically infected with B. gibsoni. However, subclinical infection was not identified in dogs of other breeds from the same geographic area.

Disruption of spermatogenesis in boars sub-clinically infected with Trypanosoma brucei brucei

Data from 14 crossbred (Landreace × Large white) boars aged 10–12 months were used to investigate specific germ cells and to what extent Sertoli cells are prone to sub-clinical infection with strain Y58/98 Trypanosome brucei brucei and effects on spermatogenesis. Boars were divided into three groups, A, B and C of 5, 5 and 4 animals, respectively. Groups A and B were infected intraperitoneally with 2.8×10 6 trypanosomes per animal. Group C consisted of intact controls. At stable sub-clinical trypanosomiasis, boars in groups A and B together with two from the controls were weighed, scrotal circumferences were measured and animals were castrated on days 56 and 84 post infection, respectively. Testes were weighed. A portion of a testis was processed for histomorphometric assessment and another portion was used to determine gonadal sperm reserves by haemocytometry. Crude cells were converted to true cells. Sub-clinical trypanosomiasis was characterised by low live and testes weights, reduced scrotal circumference, scanty parasitemia peaks at long intervals and decreased libido. Histomorphometry of animals infected with T. brucei brucei revealed somniferous tubular distortion, denudation and or degeneration of germ cells and Sertoli cells leading to distortion of spermatogenesis. Spermatids and young primary spermatocytes were most prone to, while Sertoli cells and spermatogonia were least affected by sub-clinical trypanosomiasis. There was evidence of regeneration of germ cells from precursor stem cells, resulting in slightly increased gonodal sperm reserves as the post infection period increased. Infected boars may not attain original fertility levels consequently. It was concluded that boars in tropical regions that harbour endemic disease should be maintained under prophylactic conditions.

The effect of subclinical Mycobacterium paratuberculosis infection on days open in Michigan, USA, dairy cows

A prospective cohort study design was used to evaluate the impact of subclinical Mycobacterium paratuberculosis infection on days open in a sample of Michigan dairy herds with a history of cows positive for M. paratuberculosis diagnosed by fecal culture. Participating herds were tested and productivity and reproduction records were monitored for 18 months. All cows ≥24 months old were tested for M. paratuberculosis infection using the ELISA and radiometric fecal-culture (RFC) techniques. Test-negative cows were re-tested at the conclusion of the monitoring period. Multivariable regression models were used. Using both tests in parallel, the overall sample apparent prevalence for M. paratuberculosis infection was 41.8% (223/533 animals tested). Adjusting for diagnostic sensitivity and specificity, this resulted in a calculated sample true prevalence of 59.9%. ELISA-positive cows (on average) had a 28-day increase in days open when compared to ELISA-negative cows ( p=0.02). The diagnostic method used to define a case altered the apparent association between paratuberculosis test status and days open. Fecal culture was a less-effective diagnostic tool for use in herds with a high prevalence of infected animals. The increase in days open in the ELISA-positive cows was an indication that perhaps reduced estrus expression or an increased post-partum anestrous period occurred in the subclinically infected ELISA-positive animals. This might have been due to a negative energy balance associated with M. paratuberculosis infection.

Prolonged perturbations of tumour necrosis factor-alpha and interferon-gamma in mice inoculated with Clostridium piliforme.

Clostridium piliforme is an obligate intracellular bacterium that causes enterohepatic disease in many animal species. C. piliforme infections are commonly subclinical in laboratory rats and mice, and little is known about host regulation of disease or of the effects of C. piliforme infections on investigations that use subclinically infected animals. To assess host regulation of subclinical C. piliforme infections and the effects of those infections on laboratory mice, the expression of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) was evaluated at 0, 1, 3, 7, 14 and 28 days after inoculation with C. piliforme. Subclinical infection was induced in weanling C. piliforme-susceptible DBA/2 or -resistant C57BL/6 mice with either a toxic or a non-toxic C. piliforme strain. Hepatic lesions and bacteria were demonstrated histologically in both mouse strains for 14 days after inoculation with the toxigenic bacterial strain, but were never demonstrated histologically following inoculation with the non-toxigenic strain. Hepatic TNF-alpha and IFN-gamma mRNA and serum protein levels were similarly elevated in both mouse strains 1 day after inoculation with both C. piliforme strains, as evaluated by reverse transcription PCR and enzyme-linked immunosorbent assays, respectively. Elevation of IFN-gamma persisted for 14 days after inoculation; TNF-alpha remained elevated at 28 days after inoculation.

Distinct innate and acquired immune responses to Leishmania in putative susceptible and resistant human populations endemically exposed to L. (Viannia) panamensis infection.

Mechanisms of constitutive and acquired susceptibility/resistance to Leishmania Viannia panamensis (L. (V ) p.) were investigated in endemically exposed human populations presenting either recurrent disease (putative susceptible) or subclinical infection (clinically resistant). Cutaneous delayed type hypersensitivity response to leishmanin was significantly lower among individuals experiencing recurrent leishmaniasis than among those whose skin test converted without developing the disease. Monocyte derived macrophages from individuals with recurrent disease were more permissive in vitro to the entry of parasites than macrophages from subclinically infected individuals. In vitro proliferation of CD4 and CD8 T lymphocytes in response to intracellular amastigotes was significantly lower among individuals with a history of recurrent disease compared with subclinically infected individuals. Linear regression analyses revealed a strong direct relationship between the production of interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and interleukin (IL)-10 by peripheral blood mononuclear cells (PBMC) from resistant (subclinically infected) individuals and no correlation in the production of these cytokines by PBMC from individuals who experienced recurrent disease. The results provide evidence of differences in the innate and acquired responses to Leishmania according to the outcome of the natural infection. These findings support the feasibility of identifying the immunological bases of innate and acquired resistance through studies in naturally exposed human populations.

The occurrence of Renibacterium salmoninarum within vaccine adhesion components from Atlantic salmon, Salmo salar L. and coho salmon, Oncorhynchus kisutch Walbaum

Renibacterium salmoninarum the causative agent of bacterial kidney disease (BKD), was cultured from intra-abdominal adhesions in farmed Atlantic salmon and captive coho salmon. A widespread adjuvant insult and fibrin exudate within the abdominal cavity of the Atlantic salmon and to a lesser extent in the coho salmon contained intra and extracellular locations of the bacterium. The fish were considered sub-clinically infected with R. salmoninarum and under normal testing regimes unlikely to have been examined for this disease. Extensive tissue adhesions may mask gross signs of BKD and convey a risk of exacerbation of a sub-clinical infection.

Reinfection in American cutaneous leishmaniasis: evaluation of clinical outcomes in the hamster model.

There is no clear understanding of the outcome of reinfection in New World cutaneous leishmaniasis, and its role in the relationship to the development of protection or secondary disease. For this reason, reinfection experiments with homologous (Leishmania panamensis-L. panamensis) and heterologous (L. major-L. panamensis) species of leishmaniae were conducted in the hamster model. The different protocols for primary infections prior to the challenge with L. panamensis were as follows: (a) L. major, single promastigote injection, (b) L. major, three booster infections, (c) L. panamensis, followed by antimonial treatment to achieve subclinical infection, (d) L. panamensis, with active lesions, (by antimonial treatment to achieve subclinical infection, (d) L. panamensis, with active lesions, (e) sham infected, naive controls. Although all reinfected hamsters developed lesions upon challenge, animals with active primary lesions due to L. panamensis, and receiving booster infections of L. major had the most benign secondary lesions (58-91% and 69-76% smaller than controls, respectively, P < 0.05). Subclinically infected animals had intermediate lesions (40-64% smaller than controls, P < 0.05), while hamsters which received a single dose of L. major had no significant improvement over controls. Our results suggested that L. major could elicit a cross protective response to L. panamensis, and that the presence and number of amastigotes persisting after a primary infection may influence the clinical outcome of reinfections.

Changes in electrical conductivity and somatic cell count between milk fractions from quarters subclinically infected with particular mastitis pathogens.

Cows with subclinical intramammary infections were identified by milk bacteriology. The mastitis pathogens included Staphylococcus aureus (n = 9), Streptococcus uberis (n = 10) and coagulase-negative staphylococci (n = 10). Samples of first fore milk, main flow milk and strippings milk fractions were collected from each quarter and laboratory measurements were made of electrical conductivity, milk fat concentration and somatic cell count. Conductivity measurements were corrected for milk fat concentration and within-cow inter-quarter conductivity ratios calculated. Repeatability estimates of all measurements between days were calculated. In the case of infected quarters, all conductivity values decreased markedly (P < 0.05) from first fore milk to main flow milk fractions. Conductivity differences between quarters of infected cows were substantially lower during the main milk flow phase. For quarters infected with Staph. aureus an increase in conductivity was observed (P < 0.05) from main flow to strippings fractions. For uninfected quarters, conductivity declined as milk fat concentration increased with successive milk fractions. Variation, both within and between milk fractions, was greater for somatic cell count than for conductivity. Differences in conductivity between milk fractions from individual infected quarters were not accounted for by changes in fat concentration and may result from the mixing of milk from infected and uninfected regions of the gland. Localized infection may produce a decrease in conductivity between fore milk and mid-flow fractions while differential drainage from an infection site in the secretory tissue may additionally produce an increase in conductivity from mid-flow to strippings fractions. Such changes may thus provide information on the location and magnitude of an infection. The results clearly demonstrate the importance of the milk fraction when using conductivity as a diagnostic of intramammary infection, the highest diagnostic sensitivity being achieved by using first fore milk samples.

The spread of Paenibacillus larvae subsp larvae infections in an apiary

SUMMARYThe culture of Paenibacillus larvae subsp. larvae from adult honey bees was used to trace the spread of P. I. larvae from colony to colony in a 20-colony apiary in which five had artificially induced American foulbrood (AFB). P. I. larvae quickly spread to the uninoculated colonies but no other colonies developed AFB. All colonies at some stage of the 24-week experimental period had P. I. larvae infected adult bees. The peak number of subclinically infected colonies was detected in week 12 when 12 colonies had P. I. larvae infected adult bees without showing clinical evidence of AFB. The prevalence of subclinical infections rapidly decreased after the removal of diseased colonies in week 19 to the point where no subclinical infections were detected in week 22. This work provides further evidence that AFB is not easily spread by drifting bees.

Therapeutic efficacy of hyperimmune bovine colostrum treatment against clinical and subclinical Cryptosporidium serpentis infections in captive snakes

Therapy based on the protective passive immunity of Hyperimmune Bovine Colostrum (HBC) (raised against Cryptosporidium parvum in dairy cows immunized during gestation) was tested for heterologous efficacy in subclinical and clinical infections of 12 captive snakes with C. serpentis. Six gastric HBC treatments of 1% snake weight at 1-week intervals each, have histologically cleared C. serpentis in three subclinically infected snakes, and regressed gastric histopathological changes in one of these snakes. In all snakes, each subsequent HBC treatment significantly decreased the number of oocysts recovered in gastric lavage eluants ( P<0.03). The treatments induced oocyst-negative gastric eluants and stools in all snakes, and improved clinical signs of infection. Clinically infected snakes displayed severe histopathological changes in the gastric region; however, the numbers of developmental stages of C. serpentis were moderate. Considering the severity of pathology, much lower than expected pathogen numbers were observed, and it is believed that clinically infected snakes did not have enough time to repair tissue damage that had occurred over the years of infection. As the HBC treatment was safe and highly efficacious, it is recommended to gastrically administer the HBC therapeutically to snakes that are clinically or subclinically infected with C. serpentis. Hyperimmune bovine colostrum can also be used in snake supportive therapy or prophylaxis.

Characterization of the subclinical phase of canine ehrlichiosis in experimentally infected beagle dogs

Beagle dogs were examined during the subclinical phase of canine ehrlichiosis under controlled conditions. Emphasis was placed on gathering data before artificial inoculation with Ehrlichia canis, and comparing these data with those of the subclinical phase of the disease. In this study all dogs were clinically healthy throughout the 6 month examination period. All subclinically infected dogs had IFA antibody titers to E. canis at a dilution varying from 1:2560 to 1:20 480. The most prominent haematological finding was mild thrombocytopenia with a concomitant increase in platelet size, seen in eight of the nine dogs examined. Leukocyte counts were statistically significantly reduced in 78% of the dogs, compared with their preinfection values, with 71% of dogs having significantly reduced absolute neutrophil counts. None of the dogs were either leukopenic nor neutropenic. Six of the nine dogs had increased serum gamma-globulin concentrations. No dogs were overtly anemic, although declines in packed cell volume, haemoglobin concentration and total erythrocyte count were detected in an inconsistent manner among the dogs. It was concluded that, the most reliable parameters for judging possible subclinical ehrlichial infection in beagle dogs was mild thrombocytopenia, together with a persistently high antibody titer to E. canis. Hypergammaglobulinemia would increase the suspicion further. Based on the results presented, routine testing of dogs in E. canis endemic areas is recommended in order to identify and treat dogs in the subclinical phase of the disease.

Relationships of milk culture status at calving with somatic cell counts and milk production of dairy heifers during early lactation on a Californian dairy

Four-quarter, composite milk samples were collected from 339 heifers calving for the first time in a large Californian dairy which consistently had low herd somatic cell counts and low prevalence of major mastitis pathogens. The milk samples were collected on average at 6.4 days post partum (range 1–17). Thirty-nine percent of the heifers were subclinically infected with coagulase-negative Staphylococcus spp. Other results were: no growth, 29%; coliform only, 16%; Streptococcus spp. only, 11%; Streptococcus spp. and coagulase-negative Staphylococcus spp. only, 4%; others, 1%. The somatic cell counts and milk production were not significantly different ( P > 0.05) between culture groups over the first five monthly Dairy Herd Improvement test periods. Somatic cell counts decreased significantly after the first test period within the Streptococcus spp. group ( P < 0.002) and Staphylococcus spp. group ( P < 0.01). Milk production was higher during most of the second and third test periods ( P < 0.03) compared with the first period. The frequency of heifers lost to analysis was not different between the culture groups. Results from this dairy indicate that subclinical infections with minor pathogens (primarily coagulasenegative Staphylococcus spp.) had no significant effect on average somatic cell counts or milk production during early to middle lactation.

Regulation of neutrophil adhesion molecules and shedding of Staphylococcus aureus in milk of cortisol- and dexamethasone-treated cows

SUMMARY The effects of 3 days of glucocorticoid administration on bovine blood neutrophil expression of l-selectin and CD18, and on the health status of mammary glands subclinically infected with Staphylococcus aureus were measured in 9 lactating Holsteins. The experiment was a 3 x 3 Latin square cross-over design, with 3 glucocorticoid treatments switched among groups of 3 cows/treatment during 3 periods. Treatments consisted of a vehicle (control, 10 ml of excipient/cow/d), cortisol (7.5,15, and 7.5 mg/cow on days 1, 2, and 3, respectively), and dexamethasone (0.04 mg/kg of body weight/cow/d for total daily dosages that ranged from 21.6 to 33.2 mg). Blood samples for immunostaining and flow cytometric analysis of l-selectin and CD18 and leukograms, as well as foremilk samples for determination of S aureus shedding, somatic cell counts, protein and fat percentages, and daily milk yields were collected repeatedly before, during, and after treatment days. Dexamethasone caused a profound, acute, short-lived down-regulation of l-selectin on neutrophils, which correlated in time to leukocytosis, mature and immature neutrophilias, increased shedding of S aureus in infected glands, and onset of high percentages of fat and protein and decreased milk yields. Dexamethasone also caused profound but delayed down-regulation of neutrophil CD18, which reached nadir simultaneously with reappearance of l-selectin-bearing neutrophils, normalized blood neutrophil counts, markedly high foremilk somatic cell counts and protein percentage, decreased S aureus shedding in milk, and finally, expression of clinical mastitis in some infected quarters. Each of these variables had returned to control (vehicle) values by the ninth (and last) sample collection day. Although cortisol treatment also decreased expression of l-selectin and CD18 on neutrophils, dosages used in this study were not sufficient to alter the number of circulating cells or to convert subclinical mammary gland infections to clinical mastitis. These results suggest that mammary gland health status can be altered by sudden exposure of blood neutrophils to glucocorticoids, because these steroid hormones caused profound down-regulation of the adhesion molecules that direct neutrophil margination and migration through the vascular endothelium. The results also reinforce the potential disease risk of treating infected animals with potent synthetic glucocorticoids, such as dexamethasone.

Immunologic markers of clinical evolution in children recently infected with Leishmania donovani chagasi.

The study attempted to identify immunologic markers for progression of Leishmania donovani chagasi infection to disease in children in an area endemic for visceral leishmaniasis (VL). [3H]thymidine uptake of lymphocytes stimulated with L. donovani chagasi antigen from children with asymptomatic infection (25,286 +/- 11,648) and from children with self-healing subclinical infection (15,511 +/- 4681) was greater (P = .001) than that observed with lymphocytes from children who progressed to classic VL (4811 +/- 2984). The interferon-gamma (IFN-gamma) levels from asymptomatic and subclinically infected children (74 +/- 90 units/ml) were higher (P = .02) than those observed in children who progressed to VL (7 +/- 8 units/ml). Absence of lymphocyte blastogenesis and IFN-gamma production were associated with progression of infection to classic VL. In the presence of these markers, children should be closely followed to identify signs and symptoms that would permit early initiation of therapy.

Microsporidiosis due to a pleistophorid in marron, Cherax tenuimanus (Smith), (Decapoda: Parastacidae)

Abstract. Microsporidiosis in the freshwater crayfish Cherax tenuimanus (Smith), or marron, was found to be due to a pleistophorid characterized by a single sporulation sequence producing eight, 16, 32 or 64 monomorphometric spores in a sporophorous vesicle with a fine two‐layered wall. Infection occurred predominantly in locomotor, cardiac and gastrointestinal striated muscle. The disease ranged from subclinical infections where haemocytic encapsulation and infiltration of the spore masses controlled its progress, to fulminant disease with multifocal infection in the absence of effective haemocytic responses. The lethal lesions in the latter cases appeared to be those in the proventriculus. Prevalence of infection and incidence of mortality were low. The same microsporidian was found in subclinically infected C. quinquecarinatus (Gray) and C. quadricarinatus (von Mortens).

Prevalence and effect of subclinical ovine progressive pneumonia virus infection on ewe wool and lamb production

Summary The prevalence of infection with ovine progressive pneumonia (opp) virus and its effects on ewe wool and lamb production were investigated in a flock of 2,976 ewes of 6 breed types (Rambouillet, Targhee, Columbia, Polypay, ¼ cross Finnsheep, and ½ cross Finnsheep). Prevalence of seropositivity was significantly (P ≤ 0.01) lower among Rambouillet and Targhee breeds (44 and 42%, respectively), intermediate in Polypay, Columbia, and ¼ cross Finnsheep (approximately 53%), and higher among ½ cross Finnsheep (62%). Seropositivity increased with age in all breed types from ll% at l year of age to 93% at ≥ 7 years of age. Lateral disease transmission is indicated by linear increase of seropositivity prevalence with increasing age, including that in sheep &gt; 6 years old. Subclinical infection with opp virus had no apparent detrimental effect on number of lambs born, lamb viability, birth weight, number of lambs weaned, or growth rate of single and twin lambs, compared with findings for noninfected sheep in the same flock. Mature ewe body weight and grease fleece weight did not differ between subclinically infected seropositive and seronegative ewes. Subclinical infection with opp virus does not appear to have an adverse economic effect on ewe wool and lamb production. Culling rate attributable to clinical manifestation of infection with opp virus must be accurately determined before the true effects of virus infection on production can be determined and an eradication program can be recommended.