Live virulent Rhodococcus equi, rather than killed or avirulent, elicits protective immunity to R. equi infection in mice

Mice inoculated intravenously with a sublethal dose of live virulent Rhodococcus equi ATCC 33701 that contained an 85-kb virulence plasmid were immune to a lethal intravenous challenge of ATCC 33701. This immunity depended upon the dose of immunization and developed rapidly: mice primed with 10(5) live ATCC 33701 eliminated the challenged bacteria more rapidly than mice primed with doses ranging from 10(2) to 10(4) bacteria, and mice given 10(5) live ATCC 33701 intravenously withstood the lethal challenge as early as 5 days after the initial inoculation. However, this protective immunity did not develop in mice immunized with doses of heat-killed ATCC 33701 ranging from 10(6) to 10(8), or in mice immunized with doses of live ATCC 33701P-, a plasmid-cured derivative (avirulent), in doses ranging from 10(5) to 10(7). These mice had positive antibody titers against R. equi at the challenge (14 days after priming). Adoptive transfer of resistance to virulent R equi was obtained with spleen cells from mice immunized with live ATCC 33701, but not monoclonal antibody to 15- to 17-kDa virulence-associated antigens. These results revealed that live ATCC 33701P-, a plasmid-cured derivative of virulent R equi, could not elicit protective immunity, and are consistent with previous observations that protective immunity was induced by live virulent, but not killed organisms.     

Seroprevalence of Toxoplasma gondii and concurrent Bartonella spp., feline immunodeficiency virus, feline leukemia virus, and Dirofilaria immitis infections in Egyptian cats

Toxoplasma gondii and Bartonella spp. are zoonotic pathogens of cats. Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLv) are related to human immunodeficiency virus and human leukemia virus, respectively, and these viruses are immunosuppressive. In the present study, the prevalence of antibodies to T. gondii , Bartonella spp., FIV, as well as FeLv and Dirofilaria immitis antigens was determined in sera from feral cats (Felis catus) from Cairo, Egypt. Using a modified agglutination test, antibodies to T. gondii were found in 172 (95.5%) of the 180 cats with titers of 1∶5 in 9, 1∶10 in 9, 1∶20 in 3, 1∶40 in 5, 1∶80 in 5, 1∶160 in 15, 1∶320 in 22, and 1∶640 or higher in 104. Thus, 57.4% had high T. gondii titers. Antibodies to Bartonella spp. were found in 105 (59.6%) of 178, with titers of 1∶64 in 45, 1∶128 in 39, 1∶256 in 13, 1∶512 in 3, 1∶1,024 in 4, and 1∶2,048 in 1 cat. Antibodies to FIV were detected in 59 (33.9%) of 174 cats. Of 174 cats tested, antigens to FeLv, and D. immitis were detected in 8 (4.6%) and 6 (3.4%) cats, respectively. The results indicate a high prevalence of T. gondii, Bartonella spp., and FIV infections in cats from Cairo, Egypt. This is the first report of Bartonella spp., and D. immitis infection in cats in Egypt.     

Persistence of Bartonella spp. stealth pathogens: from subclinical infections to vasoproliferative tumor formation

Bartonella spp. are facultative intracellular bacteria that typically cause a long-lasting intraerythrocytic bacteremia in their mammalian reservoir hosts, thereby favoring transmission by blood-sucking arthropods. In most cases, natural reservoir host infections are subclinical and the relapsing intraerythrocytic bacteremia may last weeks, months, or even years. In this review, we will follow the infection cycle of Bartonella spp. in a reservoir host, which typically starts with an intradermal inoculation of bacteria that are superficially scratched into the skin from arthropod feces and terminates with the pathogen exit by the blood-sucking arthropod. The current knowledge of bacterial countermeasures against mammalian immune response will be presented for each critical step of the pathogenesis. The prevailing models of the still-enigmatic primary niche and the anatomical location where bacteria reside, persist, and are periodically seeded into the bloodstream to cause the typical relapsing Bartonella spp. bacteremia will also be critically discussed. The review will end up with a discussion of the ability of Bartonella spp., namely Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis, to induce tumor-like vascular deformations in humans having compromised immune response such as in patients with AIDS.     

Leishmania donovani: cellular and humoral immune responses after primary and challenge infections in squirrel monkeys, Saimiri sciureus

Cellular and humoral immune responses were studied in squirrel monkeys after primary and challenge infection with a Khartoum strain (WR 378) of Leishmania donovani. Each of 7 squirrel monkeys, Saimiri sciureus, was inoculated intravenously with 5 X 10(7) amastigotes/kg body weight, and one other monkey (control) was inoculated with uninfected hamster spleen homogenate. Five infected monkeys recovered from visceral leishmaniasis and two infected monkeys died. Three of the five squirrel monkeys which recovered from the primary infection demonstrated acquired resistance when challenged with an intravenous inoculation of 1.0 X 10(8) amastigotes of L. donovani/kg of body weight. Each of these same three monkeys, the two remaining monkeys which recovered from the primary infection and an uninfected control monkey, were challenged subsequently with an intradermal injection of 2.2 X 10(7) promastigotes of L. braziliensis panamensis (WR539) and developed cutaneous lesions. The reactivity of peripheral blood leukocytes from infected squirrel monkeys to phytohemagglutinin was depressed 2 to 10 weeks after infection, and the reactivity to concanavalin A was not affected. Data on responses to pokeweed mitogen were inconclusive. Reactivity to leishmanial antigens was detected at 12 weeks after infection, which coincided with a marked decrease or disappearance of parasites in liver imprints. Two of five surviving squirrel monkeys developed weak delayed skin test responses to leishmanin antigens after 23 weeks; the three remaining monkeys were anergic during the primary infection but developed strong delayed skin test responses to leishmanin antigens at 7 weeks after a challenge with L. donovani. All squirrel monkeys inoculated with L. donovani developed a hyperproteinemia, hypergammaglobulinemia, hypoalbuminemia, and a reversal of the albumin/globulin ratio between 4 to 18 weeks after infection. Plasma IgM and IgG levels were increased between 2 to 18 weeks after infection; much of this increase was due to IgG. Class-specific antileishmanial antibodies, with generally low IgM and high IgG titers, reached a maximum after 14 and 16 weeks, respectively. A correlation was observed between concentration of gamma-globulins and plasma IgM and IgG levels, but not gamma-globulin concentrations and maximum titers of class-specific antileishmanial antibodies. Squirrel monkeys challenged with L. donovani again developed hyperproteinemia, hypergammaglobulinemia, and increased concentrations of plasma IgM and IgG which correlated with high titers of IgG class-specific antileishmanial antibody 4 weeks after reinoculation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Attenuated Salmonella enterica serovar Typhi and Shigella flexneri 2a strains mucosally deliver DNA vaccines encoding measles virus hemagglutinin,inducing specific immune responses and protection in cotton rats

Measles remains a leading cause of child mortality in developing countries. Residual maternal measles antibodies and immunologic immaturity dampen immunogenicity of the current vaccine in young infants. Because cotton rat respiratory tract is susceptible to measles virus (MV) replication after intranasal (i.n.) challenge, this model can be used to assess the efficacy of MV vaccines. Pursuing a new measles vaccine strategy that might be effective in young infants, we used attenuated Salmonella enterica serovar Typhi CVD 908-htrA and Shigella flexneri 2a CVD 1208 vaccines to deliver mucosally to cotton rats eukaryotic expression plasmid pGA3-mH and Sindbis virus-based DNA replicon pMSIN-H encoding MV hemagglutinin (H). The initial i.n. dose-response with bacterial vectors alone identified a well-tolerated dosage (1 x 10(9) to 7 x 10(9) CFU) and a volume (20 micro l) that elicited strong antivector immune responses. Animals immunized i.n. on days 0, 28, and 76 with bacterial vectors carrying DNA plasmids encoding MV H or immunized parenterally with these naked DNA vaccine plasmids developed MV plaque reduction neutralizing antibodies and proliferative responses against MV antigens. In a subsequent experiment of identical design, cotton rats were challenged with wild-type MV 1 month after the third dose of vaccine or placebo. MV titers were significantly reduced in lung tissue of animals immunized with MV DNA vaccines delivered either via bacterial live vectors or parenterally. Since attenuated serovar Typhi and S. flexneri can deliver measles DNA vaccines mucosally in cotton rats, inducing measles immune responses (including neutralizing antibodies) and protection, boosting strategies can now be evaluated in animals primed with MV DNA vaccines.     

Intranasal immunization of mice against Naegleria fowleri

The purpose of this research was to determine whether mice could be protected from lethal challenge with Naegleria fowleri by prior intranasal exposure to pathogenic and nonpathogenic Naegleria. Mortality ranged from 0 to 100% for mice inoculated intranasally (i.n.) with 5 x 10(3) amebae of 13 human isolates of N. fowleri. Mice were immunized and challenged i.n. using live amebae of strains of low, medium, and high virulence. The greatest protection against lethal challenge was afforded by three immunizing doses of 10(3) amebae per dose of the strain of medium virulence. Nonpathogenic N. gruberi also was used to immunize mice i.n. against lethal challenge with N. fowleri. Protection was greater following immunization with N. gruberi than it was after immunization with N. fowleri, suggesting that nonpathogenic N. gruberi may be a better immunogen in protecting mice against lethal naeglerial challenge.     

Specific cross-protective antigonococcal immunity in the murine genital tract

Specific acquired immunity to gonococci was studied in systemically immunized mice, challenged with 10(7) gonococci by intrauterine inoculation. Protection after intraperitoneal immunization was monitored by vaginal cultures taken 24 h post-challenge, since events during the first 24 h postexposure to gonococci are crucial in determining the outcome of infection. Mice were protected against gonococcal challenge by two inoculations with either live or boiled gonococci given 4 weeks apart, whereas immunization with one inoculation did not protect against challenge 1 week later. Protection was correlated with high titers of IgG antibody in serum after two immunizations, but not with the high titers of serum IgM antibody found after the one immunization. IgG antibodies, but not IgM antibodies, were shown to pass into genital secretions. Protection could be passively transferred by serum with high titers of antibody. Of most practical importance was the finding that not only were heat-stable antigens protective, but also heterologous protection resulted after immunization with three strains differing in source (disseminated gonococcal infection versus gonorrhea), opacity-transparency characteristics, and serum sensitivity. The data indicate that IgG antibodies resulting from systemic immunization with heat-stable antigens may be able to provide cross-protection immunity against gonorrhea.     

Mixed infections, cryptic diversity, and vector-borne pathogens: evidence from Polygenis fleas and Bartonella species

Coinfections within hosts present opportunities for horizontal gene transfer between strains and competitive interactions between genotypes and thus can be a critical element of the lifestyles of pathogens. Bartonella spp. are Alphaproteobacteria that parasitize mammalian erythrocytes and endothelial cells. Their vectors are thought to be various biting arthropods, such as fleas, ticks, mites, and lice, and they are commonly cited as agents of various emerging diseases. Coinfections by different Bartonella strains and species can be common in mammals, but little is known about specificity and coinfections in arthropod vectors. We surveyed the rate of mixed infections of Bartonella in flea vectors (Polygenis gwyni) parasitizing cotton rats (Sigmodon hispidus) in which previous surveys indicated high rates of infection. We found that nearly all fleas (20 of 21) harbored one or more strains of Bartonella, with rates of coinfection approaching 90%. A strain previously identified as common in cotton rats was also common in their fleas. However, another common strain in cotton rats was absent from P. gwyni, while a rare cotton rat strain was quite common in P. gwyni. Surprisingly, some samples were also coinfected with a strain phylogenetically related to Bartonella clarridgeiae, which is typically associated with felids and ruminants. Finally, a locus (pap31) that is characteristically borne on phage in Bartonella was successfully sequenced from most samples. However, sequence diversity in pap31 was novel in the P. gwyni samples, relative to other Bartonella previously typed with pap31, emphasizing the likelihood of large reservoirs of cryptic diversity in natural populations of the pathogen.     

Measles virus replication in lungs of hispid cotton rats after intranasal inoculation.

Hispid cotton rats were inoculated intranasally with either measles virus (MV) Edmonston, a multipassaged, tissue culture-adapted strain of MV, or with one of three clinical MV isolates that had limited passages (three to five times) in tissue culture cells. MV Edmonston was recovered from the lungs of every (n = 37) hispid cotton rat inoculated with this virus for at least 7 days after virus inoculation. Peak pulmonary titers occurred on Day +4 (3.3-4.4 log10/g lung). Scattered areas of inflammation were observed interstitially in lung sections from infected animals stained with hematoxylin and eosin, and a similar pattern of diffuse fluorescence was seen in cryostat sections stained with an indirect fluorescent antibody procedure specific for virus antigens. Fluorescent antibody and virus isolation studies on lung lavage cells both suggested that lung leukocytes were a primary target of the virus. In contrast to these findings, virus was isolated only sporadically from hispid cotton rats inoculated with any of the clinical measles virus isolates. Despite the restricted growth of MV in these animals, cotton rats may be useful for studying certain aspects of measles virus pathogenesis and for screening potential antiviral compounds in vivo.     

Immunization of pigs with the attenuated S- strain of Japanese encephalitis virus.

The attenuated S- strain of Japanese encephalitis virus was produced from a wild strain of this virus by serial cultivation in primary bovine kidney cell cultures at 30 degrees C. Pigs were inoculated with it and examined for ability to produce antibody and protect themselves from infection with a wild strain used for challenge. In pigs inoculated with a single dose of 10(6.5) approximately 10(7.5) TCID50 of the S- strain, the neutralizing antibody titer or hemagglutination-inhibiting antibody (HI) titer increased to 10 approximately 320. An antibody titer exceeding 10 was maintained for 2 approximately 9 weeks. In pigs inoculated twice with 10(6.5) approximately 10(7.0) TCID50 of the S- strain, HI titer increased to 80 approximately 640. In many of these pigs, HI titers of 80 approximately 160 persisted for more than 6 weeks. Pigs inoculated once or twice with 10(7.0) approximately 10(7.5) TCID50 of the S- strain were challenged by inoculation with 10(4.5) approximately 10(5.5) TCID50 of a wild strain and examined for the occurrence of viremia. As a result, an ability to protect from infection was demonstrated in pigs which showed an antibody titer surpassing 10 at the time of challenge. Pregnant sows inoculated with 10(7.0) TCID50 of the S- strain were challenged by inoculation with 10(7.0) TCID50 of a wild strain. Neither death nor infection occurred to any fetus harbored by them. From these results, it is concluded that the S- strain can be used as live virus vaccine for porcine practice.     

Enhancement of respiratory syncytial virus pulmonary pathology in cotton rats by prior intramuscular inoculation of formalin-inactiva ted virus.

Cotton rats previously inoculated with Formalin-inactivated respiratory syncytial virus (RSV) were challenged intranasally with live RSV to induce an enhancement of RSV disease similar to that observed after the administration of Formalin-inactivated RSV vaccine to human infants 20 years ago. Within 24 h after infection with RSV, cotton rats developed pulmonary lesions that reached a maximum by day 4. Histologically, the lesions resembled an experimental pulmonary Arthus reaction. An action of Formalin on RSV appears to be responsible for this effect, because live virus or virus heated in the absence of Formalin did not induce enhanced immunopathology. Selected epitopes on the fusion (F) or attachment (G) or both RSV surface glycoproteins that are involved in inducing neutralizing antibodies were modified to reduce or ablate their antigenicity. However, other epitopes on the F or G or both glycoproteins were not ablated by Formalin, because cotton rats inoculated parenterally with a Formalin-inactivated virus developed a high level of F and G antibodies measurable by an enzyme-linked immunosorbent assay. At this time, the effect of Formalin on RSV cannot be localized to either the F or G glycoprotein of RSV.     

Highly efficient induction of protective immunity by a vaccinia virus vector defective in late gene expression

Vaccinia viruses defective in the essential gene coding for the enzyme uracil DNA glycosylase (UDG) do not undergo DNA replication and do not express late genes in wild-type cells. A UDG-deficient vaccinia virus vector carrying the tick-borne encephalitis (TBE) virus prM/E gene, termed vD4-prME, was constructed, and its potential as a vaccine vector was evaluated. High-level expression of the prM/E antigens could be demonstrated in infected complementing cells, and moderate levels were found under noncomplementing conditions. The vD4-prME vector was used to vaccinate mice; animals receiving single vaccination doses as low as 10(4) PFU were fully protected against challenge with high doses of virulent TBE virus. Single vaccination doses of 10(3) PFU were sufficient to induce significant neutralizing antibody titers. With the corresponding replicating virus, doses at least 10-fold higher were needed to achieve protection. The data indicate that late gene expression of the vaccine vector is not required for successful vaccination; early vaccinia virus gene expression induces a potent protective immune response. The new vaccinia virus-based defective vectors are therefore promising live vaccines for prophylaxis and cancer immunotherapy.     

鱼类三种致病菌的粗脂多糖对异育银鲫的免疫原性

用温酚法从柱状嗜纤维菌、嗜水气单胞菌和鳗弧菌中提取的粗脂多糖（LPS）作为免疫原,分别接种异育银鲫后,通过测定受免鱼的交叉凝集抗体效价,头肾和血液中吞噬细胞的吞噬活性和用A.hydrophila活菌攻毒的方法,探讨鱼类3种致病菌的粗LPS对异育银鲫免疫原性的试验结果,结果表明,从3种致病菌中提取的粗LPS对异育银鲫均具有较强的免疫原性,受免鱼的血清中存在对3种致病菌的交叉凝集抗体;与对照鱼相比,头肾和血液中吞噬细胞的吞噬活性明显上升,受免鱼的A.hydrophila活菌攻毒均产生了较强的免疫保护力,说明在每种供试菌的粗LPS上都不同程度地存在3种致病菌的共同保护性抗原。     

Bovine respiratory syncytial virus protects cotton rats against human respiratory syncytial virus infection.

Human respiratory syncytial virus (HRSV) is the most frequent cause of severe respiratory infections in infancy. No vaccine against this virus has yet been protective, and antiviral drugs have been of limited utility. Using the cotton rat model of HRSV infection, we examined bovine respiratory syncytial virus (BRSV), a cause of acute respiratory disease in young cattle, as a possible vaccine candidate to protect children against HRSV infection. Cotton rats were primed intranasally with graded doses of BRSV/375 or HRSV/Long or were left unprimed. Three weeks later, they were challenged intranasally with either BRSV/375, HRSV/Long (subgroup A), or HRSV/18537 (subgroup B). At intervals postchallenge, animals were sacrificed for virus titration and histologic evaluation. Serum neutralizing antibody titers were determined at the time of viral challenge. BRSV/375 replicated to low titers in nasal tissues and lungs. Priming with 10(5) PFU of BRSV/375 effected a 500- to 1,000-fold reduction in peak nasal HRSV titer and a greater than 1,000-fold reduction in peak pulmonary HRSV titer upon challenge with HRSV/Long or HRSV/18537. In contrast to priming with HRSV, priming with BRSV did not induce substantial levels of neutralizing antibody against HRSV and was associated with a delayed onset of clearance of HRSV upon challenge. Priming with BRSV/375 caused mild nasal and pulmonary pathology and did not cause exacerbation of disease upon challenge with HRSV/Long. Our findings suggest that BRSV may be a potential vaccine against HRSV and a useful tool for studying the mechanisms of immunity to HRSV.     

Antibodies to lipopolysaccharide and outer membrane proteins of Salmonella enteritidis PT4 are not involved in protection from experimental infection

BALB/c and Schofield mice were inoculated with formalin-killed bacteria prepared from strains of Salmonella enteritidis belonging to phage type (PT) 4 and carrying a 38 MDa plasmid and expressing long-chain lipopolysaccharide, or strains without a 38 MDa plasmid or lacking the ability to express lipopolysaccharide. Vaccinated mice were challenged with viable bacteria belonging to a virulent strain of S. enteritidis (PT4). Mice surviving this viable challenge were examined for a humoral antibody response to membrane antigens of S. enteritidis (PT4) that might relate to the possession of a given virulence property. BALB/c mice immunized with any of the test antigens were found to be immune to S. enteritidis (PT4), and this immunity was protective. Serum antibodies, of the IgG class, were detected to OmpA and a minor outer membrane protein (OMP) of 31 kDa. Schofield mice also raised IgG antibodies to these outer membrane proteins; however, non-immunized mice of this strain were resistant to infection. The virulence of S. enteritidis (PT4) was also tested using mice belonging to strains B10D2 (new), Biozzi (high), Biozzi (low), C3HeJ, B10ITYR and C57/L.     

Concentration effects of Winogradskyella sp. on the incidence and severity of amoebic gill disease

To study the concentration effects of the bacterium Winogradskyella sp. on amoebic gill disease (AGD), Atlantic salmon Salmo salar were pre-exposed to 2 different doses (10(8) or 10(10) cells 1(-1)) of Winogradskyella sp. before being challenged with Neoparamoeba spp. Exposure of fish to Winogradskyella sp. caused a significant increase in the percentage of AGD-affected filaments compared with controls challenged with Neoparamoeba only; however, these percentages did not increase significantly with an increase in bacterial concentration. The results show that the presence of Winogradskyella sp. on salmonid gills can increase the severity of AGD.     

Infection of SDAV-immune rats with SDAV and rat coronavirus

Infection of rats with sialodacryoadenitis virus (SDAV) or rat coronavirus (RCV) is acute and self-limiting, and elimination and control of either virus is based on the assumption that recovered rats are immune to reinfection. To test this hypothesis, we examined whether SDAV-immune rats could be infected with RCV or reinfected with SDAV. Sprague Dawley (SD) rats were inoculated intranasally with SDAV or with culture medium alone and serial SDAV antibody titers were obtained. Eleven months after inoculation, when antibody titers had stabilized, SDAV-immune and nonimmune rats were challenged with SDAV or RCV, and euthanatized 3 or 6 days later. SDAV-immune rats challenged with SDAV or RCV manifested acute rhinitis associated with virus antigen by 3 days after inoculation, but no lesions or antigen were subsequently found in the lower respiratory tract, salivary glands or lacrimal glands. There was also a marked anamnestic increase in antibody titer by 6 days after challenge. SDAV-immune rats challenged with SDAV or RCV also transmitted infection to nonimmune cage mates. This study indicates that 11 months after primary infection with SDAV, rats can be infected with SDAV or RCV, but that the severity of disease is significantly reduced.     

Louse-borne bacterial pathogens in lice (Phthiraptera) of rodents and cattle from Egypt

We collected 1,023 lice, representing 5 species, from rats and domestic cattle throughout 13 governorates in Egypt and tested these lice for Anaplasma marginale, Bartonella spp., Brucella spp., Borrelia recurrentis, Coxiella burnetii, Francisella tularensis, and Rickettsia spp. by PCR amplification and sequencing. Five different louse-borne bacterial agents were detected in lice from rodents or cattle, including "Bartonella rattimassiliensis", "B. phoceensis", and Bartonella sp. near Bartonella tribocorum, Coxiella burnetii, and Rickettsia typhi. More lice from governorates bordering the Mediterranean and Red Seas contained pathogens. Our data indicate that lice of urban and domestic animals harbor pathogenic or potentially pathogenic bacterial agents throughout Egypt.     

Immunohistochemistry of great scallop Pecten maximus larvae experimentally challenged with pathogenic bacteria

Three challenge experiments were carried out on larvae of the great scallop Pecten maximus. Larvae were bath-challenged with Vibrio pectenicida and 5 strains resembling Vibrio splendidus and one Pseudoalteromonas sp. Unchallenged larvae were used as negative controls. The challenge protocol was based on the use of a multidish system, where the scallop larvae (10, 13 and 15 d post-hatching in the 3 experiments, respectively) were distributed to 2 ml wells with stagnant seawater and exposed to the bacterial cultures by bath challenge. Presence of the challenge bacteria in the wells was verified by polymerase chain reaction (PCR). A significantly increased mortality was found between 24 and 48 h in most groups challenged with V. pectenicida or V. splendidus-like strains. The exception was found in larval groups challenged with a Pseudoalteromonas sp. LT 13, in which the mortality rate fell in 2 of the 3 challenge experiments. Larvae from the challenge experiments were studied by immunohistochemistry protocol. Examinations of larval groups challenged with V. pectenicida revealed no bacterial cells, despite a high degree of positive immunostaining. In contrast, intact bacterial cells were found in larvae challenged with V. splendidus. In the case of larvae challenged with the Pseudoalteromonas sp., positive immuno-staining was limited to visible bacteria inside the digestive area and cells of the mucosa. The experiments confirm that V. splendidus and V. pectenicida are pathogenic to scallop larvae, and that the Pseudoalteromonas strain is probably not a primary pathogen, although it cannot be ruled out as a secondary pathogen.     

Effect of immunization of channel catfish with inactivated trophonts on serum and cutaneous antibody titers and survival against Ichthyophthirius multifiliis

Two trials were conducted to determine the effect of immunization of channel catfish with inactivated trophonts on serum and cutaneous antibody titers and survival against Ichthyophthirius multifiliis Fouquet (Ich). In trial I, catfish were immunized intraperitoneally (IP) with: 1) 1% formalin-inactivated trophonts, 2) 3% formalin-inactivated trophonts and 3) freeze-thawed trophonts. Positive and negative control catfish were immunized with live theronts and 5% bovine serum albumin (BSA), respectively. At day 14, 28 and 50 post-immunizations, no statistical difference was noted in serum or cutaneous anti-Ich antibody titers to formalin-inactivated trophonts or freeze-thawed trophonts. The survival of catfish challenged with live theronts ranged from 33.3% to 43.3% for the formalin-inactivated or freeze-thawed trophonts at 50 d post-immunization. The survival of catfish immunized with live theront and BSA was 93.3 and 0%, respectively. In trial II, catfish were IP immunized with sonicated trophonts at doses of 1) 5 trophonts or 10.2 microg protein g(-1) fish, 2) 10 trophonts or 20.4 microg protein g(-1) fish, 3) 20 trophonts or 40.8 microg protein g(-1) fish, and 4) 5% BSA as the control. Fish immunized with 10 or 20 trophonts g(-1) fish showed highest serum (1/210 to 1/480) and cutaneous antibody titers (1/48 to 1/52), respectively, at 22 d post-immunization and survival (63.3-60.0%). The fish immunized with 5 trophonts g(-1) fish had titers of 1/52 and 1/12 for serum and cutaneous antibody and survival of 23.3%. BSA immunized catfish had background titers and a survival of 6.7%. There was a significant correlation between doses of sonicated trophonts used to immunize and catfish survival (correlation coefficient = 0.859, p < 0.01). These results indicate that doses of sonicated trophonts, but not formalin-inactivated or freeze-thawed trophonts provided both serum and cutaneous antibody responses and survival to live trophont challenge.