Oral delivery of Hyperimmune bovine serum antibodies against CS6-expressing enterotoxigenic Escherichia coli as a prophylactic against diarrhea

BACKGROUND

. Oral administration of bovine antibodies active against enterotoxigenic Escherichia coli (ETEC) have demonstrated safety and efficacy against diarrhea in human challenge trials. The efficacy of bovine serum immunoglobulins (BSIgG) against recombinant colonization factor CS6 or whole cell ETEC strain B7A was assessed against challenge with the CS6-expressing B7A.

METHODS

. This was a randomized, double-blind, placebo-controlled trial in which healthy adults received oral hyperimmune BSIgG anti-CS6, anti-B7A whole cell killed or non-hyperimmune BSIgG (placebo) in a 1:1:1 ratio then challenged with ETEC B7A. Two days pre-challenge, volunteers began a thrice daily, seven day course of immunoprophylaxis. On day 3, subjects received 1 × 10¹⁰ CFUs of B7A. Subjects were observed for safety and the primary endpoint of moderate-severe diarrhea (MSD).

RESULTS

. A total of 59 volunteers received product and underwent ETEC challenge. The BSIgG products were well-tolerated across all subjects. Upon challenge, 14/20 (70%) placebo recipients developed MSD, compared to 12/19 (63%; p = .74) receiving anti-CS6 BSIgG and 7/20 (35%; p = .06) receiving anti-B7A BSIgG. Immune responses to the ETEC infection were modest across all groups.

CONCLUSIONS

. Bovine-derived serum antibodies appear safe and well tolerated. Antibodies derived from cattle immunized with whole cell B7A provided 50% protection against MSD following B7A challenge; however, no protection was observed in subjects receiving serum antibodies targeting CS6. The lack of observed efficacy in this group may be due to low CS6 surface expression on B7A, the high dose challenge inoculum and/or the use of serum derived antibodies versus colostrum-derived antibodies.

Comparison of the antibody in lymphocyte supernatant (ALS) and ELISPOT assays for detection of mucosal immune responses to antigens of enterotoxigenic Escherichia coli in challenged and vaccinated volunteers

In the present study we compared the ELISPOT and antibody in lymphocyte supernatants (ALS) assays as surrogate measures of mucosal immunity. In separate studies, 20 inpatient volunteers received oral doses of 6 x 10(8) or 4 x 10(9)cfu of ETEC strain E24377A (LT+, ST+, CS1+, CS3+) and 20 subjects received 1 (n = 9) or 2 (n = 11) oral doses of the attenuated ETEC vaccine, PTL-003 expressing CFA/II (CS1+ and CS3+) (2 x 10(9)cfu/dose). Peripheral blood mononuclear cells (PBMCs) from all subjects were assayed for anti-colonization factor or toxin-specific IgA antibody responses using the ALS and ELISPOT procedures. ALS responses were measured using a standard ELISA, as well as by time-resolved fluorescence (TRF). Following challenge with E24377A, significant anti-CS3, CS1 and LT ALS responses were detected in the lymphocyte supernatants of 75-95% of the subjects. A similar proportion (75%) of subjects mounted an ALS response to CFA/II antigen after vaccination with the PTL-003 vaccine. Inter-assay comparisons between ALS and ELISPOT methods also revealed a high degree of correlation in both immunization groups. ALS sensitivity versus the ELISPOT assay for LT, CS3 and CS1-specific responses following challenge were 95%, 94% and 78%, respectively and 83% for the ALS response to CFA/II antigen after vaccination with PTL-003. Correlation coefficients for the LT and CS3 antigens were 0.94 (p<0.001) and 0.82 (p<0.001), respectively after challenge and 0.78 (p<0.001) after vaccination. The association between ALS and ELISPOT for the CS1 antigen was however, significant only when ALS supernatants were tested by TRF (r = 0.91, p<0.001). These results demonstrate the value and flexibility of the ALS assay as an alternative to ELISPOT for the measurement of mucosal immune responses to ETEC antigens, particularly when the complexities of ELISPOT may make it impractical to perform.

Safety and immunogenicity of an oral, inactivated, whole-cell vaccine for Shigella sonnei: preclinical studies and a Phase I trial

Orally delivered, inactivated whole-cell vaccines are safe methods of inducing local and systemic immunity. To increase surface proteins associated with adherence and invasion, Shigella sonnei were grown in BHI broth containing deoxycholate. A whole-cell vaccine (SsWC) was then produced by formalin inactivation. In pre-clinical studies, the SsWC vaccine was immunogenic and protected against S. sonnei-induced keratoconjunctivitis in the guinea pig model. In a randomized, double-blind, placebo-controlled, Phase I study, 10 evaluable subjects received either three doses of SsWC on Days 0, 14, and 28 (N = 3); five doses of SsWC on Days 0, 2, 4, 6, and 28 (N = 4); or placebo (N = 3). Each dose contained 2.0 x 10(10) inactivated cells. Serum and fecal antibodies against SsWC, LPS, and IpaC were measured by ELISA. A > or = 4-fold increase in titer was considered significant. Both SsWC dosing regimens were well tolerated. No fever or severe gastrointestinal symptoms were noted by any of the vaccinated subjects. Antibody responses were similar in the two dosing groups. Serum IgG or IgA responses to SsWC were seen in six of seven vaccinees (86%), to LPS in four of seven (57%), and to IpaC in five of seven (61%). Fecal IgA responses to these three antigens developed in five of five, three of five, and three of five subjects, respectively. Among the seven vaccinees, geometric mean rises in serum IgA levels to all three immunogens were significant; IgG increases trended toward significance (paired one-tailed t-test). We conclude that SsWC was immunogenic and protective in animal studies and well tolerated and immunogenic in a Phase I trial.

Prevention of disease in ferrets fed an inactivated whole cell Campylobacter jejuni vaccine

Ferrets were used to demonstrate the potential of a killed whole cell vaccine prepared from Campylobacter jejuni to protect against disease. C. jejuni strain 81-176 was grown in BHI broth, formalin-fixed, and resuspended in PBS to a concentration of 10(10) cells per ml. This vaccine (CWC) or live organisms were delivered orally with a nasogastric tube into anesthetized animals treated to reduce gastric acidity and intestinal motility. When 5x10(10) CFU of the vaccine strain (Lior serotype 5) or one of two other serotypes, CGL-7 (Lior 4) or BT44 (Lior 9), was used to challenge the ferrets, all of the animals developed a mucoid diarrhea. If the animals had been challenged with 5x10(9) CFU of the homologous strain 1 month before challenge with 10(10) CFU, 80-100% protection against disease was seen. This protection was also obtained after an initial exposure to the 81-176 strain followed by challenge with either of the heterologous strains. CWC was used to see if protection demonstrated with the live organisms could be produced with the non-living preparation. When 10(9) cells of CWC was given as two doses 7 days apart with or without 25mug of a coadministered mucosal adjuvant, LT(R192G), only 40-60% of the animals were protected. If the regimen was changed to four doses given 48h apart, 80% of the animals were free of diarrhea after subsequent challenge. Increasing the number of cells in the four dose regimen to 10(10) cells did not improve protection. Animals given four doses of 10(10) cells combined with LT(R192G) were subsequently challenged with 10(10) cells of the homologous strain or the heterologous strain CGL-7. The CWC protected against both strains. Serum IgG antibody titers determined by ELISA showed little increase following the CWC four dose vaccination regimen, compared to animals given one dose of the live organism. On subsequent challenge, however, both CWC vaccinated and live-challenged ferrets showed comparable antibody titer increases above those obtained following the initial challenge or vaccination. Western blots were used to show that the immunodominant antigen in vaccinated animals was a 45kDa protein, while in ferrets challenged with live organisms the immunodominant antigen was a 62kDa protein. These data show that the CWC can be used to protect against disease caused by Campylobacter. They also show that protection and serum IgG responses do not depend upon the use of the mucosal adjuvant and that cross protection among some of the major serotypes of Campylobacter responsible for human disease is possible.

Pre-exposure anti-Campylobacter jejuni immunoglobulin a levels associated with reduced risk of Campylobacter diarrhea in adults traveling to Thailand

Diarrhea history questionnaires were administered to 369 U.S. military volunteers before and after deployment to Thailand. Additionally, blood samples obtained from a subset of 221 volunteers 1-3 weeks previously and 3-4 weeks after their deployment were tested by enzyme-linked immunosorbent assay for immunoglobulin A to Campylobacter jejuni. Stool samples from personnel (including volunteers) contracting diarrhea in Thailand were cultured for enteric pathogens. Overall, 35.2% (130 of 369) of questionnaire respondents reported one or more diarrhea episodes during their trip. Volunteers with pretravel anti-C. jejuni reciprocal titers < or = 450 were 1.6 times as likely to have had diarrhea during their stay in Thailand compared with those with pretravel titers > 450 (39.7% versus 25.3%; P = 0.05). The symptomatic seroconversion, or attributable Campylobacter diarrhea attack rate, for the 1-month exercise was 12.7% (28 of 221). The symptomatic seroconversion rate in nonimmune (titer < or = 450) volunteers was 17.1%, whereas that in immune volunteers was only 4.0% (P = 0.002). Campylobacter jejuni or C. coli were recovered from 32.9% (56 of 170) of stool samples cultured and were the most commonly identified enteropathogens. Campylobacter diarrhea was associated with elevated temperatures, fecal red cells, and fecal white blood cells. The results of this study show that Campylobacter continues to represent a significant health threat to Western travelers to Thailand, but many of these travelers have preexisting Campylobacter immunity that protects them from clinically significant Campylobacter enteritis.

Campylobacter jejuni enteritis

We report the development of Campylobacter jejuni enteritis in a patient with preexisting humoral and cellular immune recognition of C. jejuni antigens. This is one of few studies in which the immunologic status of a person with regard to C. jejuni before and after C. jejuni infection is directly compared, and it is the only study of which we are aware that includes measurements of cellular immunity. The findings may be important to Campylobacter vaccine development efforts.

Early diagnosis of scrub typhus with a rapid flow assay using recombinant major outer membrane protein antigen (r56) of Orientia tsutsugamushi

The variable 56-kDa major outer membrane protein of Orientia tsutsugamushi is the immunodominant antigen in human scrub typhus infections. We developed a rapid immunochromatographic flow assay (RFA) for the detection of immunoglobulin M (IgM) and IgG antibodies to O. tsutsugamushi. The RFA employs a truncated recombinant 56-kDa protein from the Karp strain as the antigen. The performance of the RFA was evaluated with a panel of 321 sera (serial bleedings of 85 individuals suspected of scrub typhus) which were collected in the Pescadore Islands, Taiwan, from 1976 to 1977. Among these 85 individuals, IgM tests were negative for 7 cases by both RFA and indirect fluorescence assay (IFA) using Karp whole-cell antigen. In 29 cases specific responses were detected by the RFA earlier than by IFA, 44 cases had the same detection time, and 5 cases were detected earlier by IFA than by RFA. For IgG responses, 4 individuals were negative with both methods, 37 cases exhibited earlier detection by RFA than IFA, 42 cases were detected at the same time, and 2 cases were detected earlier by IFA than by RFA. The sensitivities of RFA detection of antibody in sera from confirmed cases were 74 and 86% for IgM and IgG, respectively. When IgM and IgG results were combined, the sensitivity was 89%. A panel of 78 individual sera collected from patients with no evidence of scrub typhus was used to evaluate the specificity of the RFA. The specificities of the RFA were 99% for IgM and 97% for IgG. The sensitivities of IFA were 53 and 73% for IgM and IgG, respectively, and were 78% when the results of IgM and IgG were combined. The RFA test was significantly better than the IFA test for the early detection of antibody to scrub typhus in primary infections, while both tests were equally sensitive with reinfected individuals.

Campylobacter jejuni cytolethal distending toxin mediates release of interleukin-8 from intestinal epithelial cells

Live cells of Campylobacter jejuni and Campylobacter coli can induce release of interleukin-8 (IL-8) from INT407 cells. Additionally, membrane fractions of C. jejuni 81-176, but not membrane fractions of C. coli strains, can also induce release of IL-8. Membrane preparations from 81-176 mutants defective in any of the three membrane-associated protein subunits of cytolethal distending toxin (CDT) were unable to induce IL-8. The presence of the three cdt genes on a shuttle plasmid in trans restored both CDT activity and the ability to release IL-8 to membrane fractions. However, CDT mutations did not affect the ability of 81-176 to induce IL-8 during adherence to or invasion of INT407 cells. When C. jejuni cdt genes were transferred on a shuttle plasmid into a C. coli strain lacking CDT, membrane preparations became positive in both CDT and IL-8 assays. Growth of C. jejuni in physiological levels of sodium deoxycholate released all three CDT proteins, as well as CDT activity and IL-8 activity, from membranes into supernatants. Antibodies against recombinant forms of each of the three CDT subunit proteins neutralized both CDT activity and the activity responsible for IL-8 release. The data suggest that C. jejuni can induce IL-8 release from INT407 cells by two independent mechanisms, one of which requires adherence and/or invasion and the second of which requires CDT.

Evaluation of a truncated recombinant flagellin subunit vaccine against Campylobacter jejuni

A recombinant protein comprising the maltose-binding protein (MBP) of Escherichia coli fused to amino acids 5 to 337 of the FlaA flagellin of Campylobacter coli VC167 was evaluated for immunogenicity and protective efficacy against challenge by a heterologous strain of campylobacter, Campylobacter jejuni 81-176, in two murine models. The sequence of the flaA gene of strain 81-176 revealed a predicted protein which was 98.1% similar to that of VC167 FlaA over the region expressed in the fusion protein. Mice were immunized intranasally with two doses of 3 to 50 microgram of MBP-FlaA, given 8 days apart, with or without 5 microgram of the mutant E. coli heat-labile enterotoxin (LT(R192G)) as a mucosal adjuvant. The full range of MBP-FlaA doses were effective in eliciting antigen-specific serum immunoglobulin G (IgG) responses, and these responses were enhanced by adjuvant use, except in the highest dosing group. Stimulation of FlaA-specific intestinal secretory IgA (sIgA) responses required immunization with higher doses of MBP-FlaA (>/=25 microgram) or coadministration of lower doses with the adjuvant. When vaccinated mice were challenged intranasally 26 days after immunization, the best protection was seen in animals given 50 microgram of MBP-FlaA plus LT(R192G). The protective efficacies of this dose against disease symptoms and intestinal colonization were 81.1 and 84%, respectively. When mice which had been immunized with 50 microgram of MBP-FlaA plus LT(R192G) intranasally were challenged orally with 8 x 10(10), 8 x 10(9), or 8 x 10(8) cells of strain 81-176, the protective efficacies against intestinal colonization at 7 days postinfection were 71.4, 71.4, and 100%, respectively.

Epidemiology of enterotoxigenic Escherichia coli diarrhea in a pediatric cohort in a periurban area of lower Egypt

Enterotoxigenic Escherichia coli (ETEC) are diverse pathogens that express heat-labile (LT) and/or heat-stable (ST) enterotoxins, yet little is known about whether epidemiologic patterns of pediatric ETEC diarrhea vary by the expressed ETEC toxin phenotype. In total, 242 Egyptian children aged <3 years were prospectively followed in 1993-1995. ETEC episodes were detected during twice-weekly home visits, and asymptomatic ETEC excretion was identified from monthly cross-sectional surveys. ETEC episodes were 0.6 per child-year. ST-only ETEC was 2.6 times (P<.001) more common in warmer than cooler months, while LT-only ETEC showed no seasonal variation. Ownership of a household sanitary latrine, but not breast-feeding, was associated with a lower risk of both enterotoxin phenotypes. Coexpression of a colonization factor by LT- or ST-only ETEC strengthened the association with diarrhea. These findings indicate that the epidemiologic patterns of LT-only and ST-only ETEC are not identical and that disease interventions should include improved household sanitation.

Campylobacter jejuni-stimulated secretion of interleukin-8 by INT407 cells

Incubation of INT407 cells with various clinical isolates of Campylobacter jejuni resulted in secretion of interleukin-8 (IL-8) at levels ranging from 96 to 554 pg/ml at 24 h. The strains which produced the highest levels of IL-8 secretion were 81-176 and BT44. Induction of IL-8 secretion required live cells of 81-176 and was dependent on de novo protein synthesis. Site-specific mutants of 81-176, which were previously shown to be defective in adherence and invasion, resulted in reduced levels of secretion of IL-8, and cheY mutants of strains 81-176 and 749, which are hyperadherent and hyperinvasive, resulted in higher levels of IL-8 secretion. Another mutant of 81-176, which adheres at about 43% of the wild-type levels but is noninvasive, also showed marked reduction in IL-8 levels, suggesting that invasion is necessary for high levels of IL-8 secretion. When gentamicin was added to INT407 cells at 2 h after infection with 81-176, IL-8 secretion 22 h later was equivalent to that of controls without gentamicin, suggesting that the events which trigger induction and release of IL-8 occur early in the interactions of bacteria and eukaryotic cells.

Mutation in the peb1A locus of Campylobacter jejuni reduces interactions with epithelial cells and intestinal colonization of mice

Campylobacter jejuni is one of the leading causes of bacterial diarrhea throughout the world. We previously found that PEB1 is a homolog of cluster 3 binding proteins of bacterial ABC transporters and that a C. jejuni adhesin, cell-binding factor 1 (CBF1), if not identical to, contains PEB1. A single protein migrating at approximately 27 to 28 kDa was recognized by anti-CBF1 and anti-PEB1. To determine the role that the operon encoding PEB1 plays in C. jejuni adherence, peb1A, the gene encoding PEB1, was disrupted in strain 81-176 by insertion of a kanamycin resistance gene through homologous recombination. Inactivation of this operon completely abolished expression of CBF1, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. In comparison to the wild-type strain, the mutant strain showed 50- to 100-fold less adherence to and 15-fold less invasion of epithelial cells in culture. Mouse challenge studies showed that the rate and duration of intestinal colonization by the mutant were significantly lower and shorter than with the wild-type strain. In summary, PEB1 is identical to a previously identified cell-binding factor, CBF1, in C. jejuni, and the peb1A locus plays an important role in epithelial cell interactions and in intestinal colonization in a mouse model.

Standardization of measurement of immunoglobulin-secreting cells in human peripheral circulation

A sensitive, and at times the most sensitive, measurement of human vaccine immunogenicity is enumeration of antibody-secreting cells (ASC) in peripheral blood. However, this assay, which is inherently capable of measurement of the absolute number of antigen-specific ASC, is not standardized. Thus, quantitative comparison of results between laboratories is not currently possible. To address this issue, isotype-specific ASC were enumerated from paired fresh and cryopreserved mononuclear cell (MNC) preparations from healthy adult volunteers resident in either the United States (US group) or Egypt (EG group). Analysis of fresh cells from US volunteers revealed mean numbers of ASC per 10(6) MNC of 617, 7,738, and 868 for immunoglobulin M (IgM), IgG, and IgA, respectively, whereas EG volunteers had 2,086, 7,580, and 1,677 ASC/10(6) MNC for the respective isotypes. Cryopreservation resulted in a slight reduction in group mean IgM, IgG, and IgA ASC (maximum reduction in group mean, 14%), but in no instance were results obtained with cryopreserved cells significantly lower than those obtained with fresh cells. To determine if cryopreservation affected the number of bacterial antigen-specific ASC detected, cells from a group of US adult volunteers who received a single oral dose of a mutated Escherichia coli heat-labile enterotoxin (LT(R192G)) were tested. There was no significant difference (P > 0.05) in the number of antigen-specific IgA or IgG ASC detected between fresh and cryopreserved MNC. The results support the views that ASC assays can be standardized to yield quantitative results and that the methodology can be changed to make the test more practical.

Murine intranasal challenge model for the study of Campylobacter pathogenesis and immunity

Campylobacter jejuni infection of mice initiated by intranasal administration was investigated as a potential model for studies of pathogenesis and immunity. By using a standard challenge (5 x 10(9) CFU), C. jejuni 81-176 was more virulent for BALB/c (72% mortality) than for C3H/Hej (50%), CBA/CAJ (30%), or C58/J (0%). Intranasal challenge of BALB/c was used to compare the relative virulence of three reference strains; C.jejuni 81-176 was more virulent (killing 83% of challenged mice) than C. jejuni HC (0%) or C. coli VC-167 (0%). The course of intranasally initiated C. jejuni 81-176 infection in BALB/c was determined. C. jejuni was recovered from the lungs, intestinal tract, liver, and spleen at 4 h after challenge, the first interval evaluated. After this initial interval, three distinct patterns of infection were recognized: (i) a progressive decline in number of C. jejuni CFU (stomach, blood, lungs), (ii) decline followed by a second peak in the number of organisms recovered at 2 or 3 days postchallenge (intestine, liver, mesenteric lymph nodes), and (iii) persistence of approximately the same number of C.jejuni CFU during the course of the experiment (spleen). Intranasally induced infection initiated with a sublethal number of bacteria or intranasal immunization with killed Campylobacter preparations resulted in both the generation of Campylobacter antigen-specific immune responses and an acquired resistance to homologous rechallenge. The model was used to evaluate the relative virulence of nine low-in vitro-passage (no more than five passages) isolates of C. jejuni species from patients with diarrhea. The patient isolates were differentially virulent for mice; one killed all exposed mice, three were avirulent (no deaths) and the remainder showed an intermediate virulence, killing 17 to 33%. Mouse virulence of Campylobacter strains showed a trend toward isolates originating from individuals with watery diarrhea; however, no association was found between mouse virulence and other signs or symptoms. There were no observed relationships between mouse virulence and bacterial Lior serotype or Fla polymorphic group. Intranasal challenge of BALB/c with C. jejuni is a useful model for the study of infection and vaccination-acquired immunity to this agent.

Serum antibody to lipopolysaccharide antigens of Shigella species among U.S. military personnel deployed to Saudi Arabia and Kuwait during Operations Desert Shield and Desert Storm

During Operations Desert Shield and Desert Storm, U.S. troops were at high risk of diarrheal disease due to Shigella spp., particularly Shigella sonnei. In order to better understand the serologic response to Shigella infection, 830 male U.S. combat troops were evaluated before and after the deployment to Saudi Arabia and Kuwait for immunoglobulin A (IgA) and IgG anti-Shigella lipopolysaccharide (LPS) (antibody to S. sonnei form I and Shigella flexneri serotypes 1a, 2a, and 3a) in serum. Just before deployment, 10.3% of the subjects were seropositive for IgA and 18.3% were positive for IgG anti-Shigella LPS. IgA and IgG anti-LPS antibody levels in serum prior to deployment were significantly associated with nonwhite race and ethnicity, birth outside the United States, and antibody to hepatitis A virus and Helicobacter pylori. During the deployment, which lasted for a mean of 131 days, 60% of the subjects reported at least one episode of diarrhea and 15% reported an episode of diarrhea with feverishness; also, 5.5% of the subjects exhibited IgA seroconversion to Shigella LPS and 14.0% exhibited IgG seroconversion. A significant association between the development of diarrheal symptoms and either positive predeployment anti-LPS antibody or seroconversion was not found. These data indicate that in this population of U.S. Desert Storm troops who were at high risk of Shigella infection, there was no apparent relation between IgA or IgG anti-Shigella LPS in serum and diarrheal disease.

Immunogenicity and protective efficacy of a prototype Campylobacter killed whole-cell vaccine in mice

The immunogenicity and efficacy of an experimental inactivated Campylobacter jejuni whole-cell (CWC) vaccine were evaluated in mice. Mice were orally immunized in a three-dose primary series (48-h intervals) at doses of 10(5), 10(7), or 10(9) CWC vaccine particles alone or in combination with 25 micrograms of a mucosal adjuvant, the heat-labile enterotoxin of Escherichia coli (LT). The comparative immunogenicities of both formulations were assessed on the basis of the generation of antigen-specific antibodies in serum and intestinal secretions, and efficacy was determined by measuring the degrees of protection afforded against intestinal colonization and systemic dissemination of challenge organisms. Campylobacter-specific intestinal immunoglobulin (Ig) A responses were dependent on the use of LT, whereas IgA and IgG responses in serum were not. Colonization resistance was induced over a broad range of vaccine doses when LT was included. However, only the highest dose of CWC alone gave comparable levels of protection. Both formulations provided equivalent protection against systemic spread of challenge organisms. These results indicate that both whole-cell vaccine formulations deserve further evaluation as candidate vaccines and also highlight the potential value of mucosal adjuvants, like LT, in enteric vaccine development.

Safety and immunogenicity of a prototype oral whole-cell killed Campylobacter vaccine administered with a mucosal adjuvant in non-human primates

The safety and immunogenicity of two prototype oral Campylobacter killed whole-cell (CWC) vaccines were tested in rhesus monkeys. Animals were immunized with a primary two-dose series (days 0 and 14) of vaccine consisting of CWC (10(10) particles/dose) given alone or in combination with 0.5-1000 micrograms of the heat-labile enterotoxin of Escherichia coli as an oral adjuvant (OA). A booster vaccination, 4 weeks after primary immunization, was given to animals receiving CWC alone or supplemented with 0.5, 5 or 50 micrograms of OA. Both CWC and CWC-OA were well tolerated, with no adverse side-effects noted. Campylobacter-specific as well as adjuvant-specific antibody-secreting cells (ASCs) were determined in peripheral blood collected 7 days after each vaccine dose. Campylobacter-specific IgA ASC responses were enhanced by OA in a dose-dependent manner (p = 0.025), while IgG ASC responses were not. Seroconversions (both IgA and IgG) to Campylobacter antigens were also enhanced in monkeys receiving adjuvanted vaccine. No significant booster vaccination effect was observed in circulating ASCs in any of the immunization groups. In vitro T-cell proliferative responses to Campylobacter jejuni antigens were somewhat enhanced in both the CWC and CWC-OA immunization groups. These results demonstrate that CWC-OA is safe and superior to CWC alone in its ability to stimulate both local and systemic Campylobacter-specific IgA and IgG responses in primates and they support its further evaluation in human clinical studies.

Campylobacter diarrhea in Alexandria, Egypt

The role of Campylobacter as a cause of bacterial diarrhea in young children in Alexandria, Egypt was investigated. Stools or rectal swabs were collected from 880 children (mean age 9.8 months) presenting to a hospital with the primary complaint of diarrhea and from 1,079 well children (mean age 8.8 months) attending a vaccination clinic. Isolation of Campylobacter was significantly (p<0.0002) more frequent from cases (17.2%) than from controls (6.4%). Campylobacter was isolated from children presenting with diarrhea more frequently than Salmonella (3% isolation rate), Shigella (2% isolation rate), or other bacterial pathogens (1% isolatoin rate). Isolation of Campylobacter was significantly more frequent during the rainy season (p<0.0012). These results implicate Campylobacter as a major bacterial cause of diarrhea for which young children are brought for medical attention in Alexandria, Egypt.

Short-course norfloxacin and trimethoprim-sulfamethoxazole treatment of shigellosis and salmonellosis in Egypt

In a double-blind clinical study, 109 adult Egyptian patients infected with Shigella spp. and 45 infected with Salmonella spp. were randomly assigned to three treatment groups: 1) norfloxacin in a single 800-mg dose, 2) norfloxacin, 400 mg twice a day for three days, and 3) trimethoprim (160 mg)-sulfamethoxazole (800 mg) (TMP-SMX), twice a day for three days. Among Shigella-infected patients, diarrheal symptoms had resolved in 86-97% and bacteriologic failure (repeat positive stool culture) occurred in only two patients five days after the start of the three treatment regimens. Among Salmonella-infected patients, diarrheal symptoms had resolved in 76-82% of patients and bacteriologic failure was common (18-36%) five days after the start of therapy. These data indicate that short-course therapy with either norfloxacin or TMP-SMX can be effectively used to treat shigellosis in adults in developing countries. However, for uncomplicated Salmonella spp. infection, short-course therapy with norfloxacin and TMP-SMX may not lead to a rapid resolution of symptoms or consistently eliminate this enteropathogen.

Development and characterization of recA mutants of Campylobacter jejuni for inclusion in attenuated vaccines

Isogenic recA mutants of Campylobacter jejuni have been constructed for evaluation of their usefulness in attenuated vaccines against this major worldwide cause of diarrhea. The recA+ gene of C. jejuni 81-176 was cloned by using degenerate primers to conserved regions of other RecA proteins in a PCR. The C. jejuni recA+ gene encodes a predicted protein with an M(r) of 37,012 with high sequence similarity to other RecA proteins. The termination codon of the recA+ gene overlaps with the initiation codon of another open reading frame which encodes a predicted protein which has > 50% identity with the N terminus of the Escherichia coli enolase protein. A kanamycin resistance gene was inserted into the cloned recA+ gene in E. coli and returned to C. jejuni VC83 by natural transformation, resulting in allelic replacement of the wild-type recA gene. The resulting VC83 recA mutant displayed increased sensitivity to UV light and a defect in generalized recombination as determined by natural transformation frequencies. The mutated recA gene was amplified from VC83 recA by PCR, and the product was used to transfer the mutation by natural transformation into C. jejuni 81-176 and 81-116, resulting in isogenic recA mutants with phenotypes similar to VC83 recA. After oral feeding, strain 81-176 recA colonized rabbits at levels comparable to wild-type 81-176 and was capable of eliciting the same degree of protection as wild-type 81-176 against subsequent homologous challenge in the RITARD (removable intestinal tie adult rabbit diarrhea) model.

Diarrhoeal disease: current concepts and future challenges. Epidemiology of diarrhoeal diseases in developed countries

Diarrhoeal diseases are a common problem in industrialized countries, resulting in appreciable morbidity and mortality. While the total burden of these illnesses is much less than that in developing countries, the same basic disease risk factors influence transmission. This article reviews selected environmental, host and pathogen-specific factors which shape the epidemiology of infectious diarrhoea in developed countries. The effective adaptation of techniques from molecular biology, such as plasmid analysis, deoxyribonucleic acid hybridization, and the polymerase chain reaction, to studies of diarrhoeal disease epidemiology is also discussed.

The Navy Forward Laboratory during Operations Desert Shield/Desert Storm

The Navy Forward Laboratory (NFL) was an advanced infectious disease laboratory which provided a theater-wide reference diagnostic capability during Operations Desert Shield/Storm. During Operation Desert Shield, when massive numbers of troops were being deployed, the NFL primarily supported medical personnel in the diagnosis and treatment of infectious diseases. During the war, the laboratory provided rapid biologic warfare diagnostic support. The NFL demonstrated the benefits of a comprehensive, on-site diagnostic laboratory when large numbers of troops are deployed to high-risk areas and demonstrated the importance of military medical research laboratories for training of scientists and physicians, threat assessment, and product development.

Diarrheal and respiratory disease aboard the hospital ship, USNS-Mercy T-AH 19, during Operation Desert Shield

Diarrhea and respiratory disease were common problems among ground troops deployed to the Middle East during Operation Desert Shield. In order to determine the prevalence and impact of diarrheal and upper respiratory disease among shipboard personnel during this period, an epidemiologic survey was conducted on the hospital ship, USNS Mercy T-AH 19. An episode of acute diarrhea was reported by 46% of the surveyed population, and 79% reported upper respiratory symptoms. Six percent of personnel were temporarily unable to perform scheduled duties due to gastrointestinal symptoms and 7% due to respiratory symptoms. Officers were at increased risk of experiencing an episode of diarrhea, and female crew members more often reported respiratory complaints. Improved strategies to prevent diarrhea and respiratory disease among shipboard personnel are needed.

Campylobacter-associated diarrhoea in Egyptian infants: epidemiology and clinical manifestations of disease and high frequency of concomitant infections

A diarrhoeal disease survey in Alexandria, Egypt determined the prevalence, seasonality, and household risk factors for Campylobacter-associated diarrhoea in young children. The study population was 880 children (mean age = 9.8 months) presenting with diarrhoea at one of two hospitals. A control group consisted of 1,079 healthy children (mean age = 8.8 months) attending two nearby vaccination clinics. The overall isolation frequencies for Campylobacter spp. were 16.8% for cases and 6.4% for the comparison group (p = 1 x 10(-8)). Other enteropathogens detected in diarrhoeal stools were: rotavirus (28.6%), Giardia lamblia trophozoites (21.3%), enterotoxigenic Escherichia coli (8.7%), Entamoeba histolytica (3.9%), Salmonella spp. (2.7%), and Shigella spp. (1.8%). There were few or no isolates of Aeromonas spp., Vibrio spp., Yersinia spp., or Plesiomonas spp. Comparisons among cases showed that Campylobacter spp. isolations were more prevalent during the rainy season (p = 0.001) and positively associated with keeping fowl in the home (p = 0.003) or having an outdoor source of drinking water (p = 0.029). Among Campylobacter-positive diarrhoeal patients, 69.0% had faecal leukocytes present and 16.3% had bloody stools. Patients with Campylobacter-positive diarrhoeal stools were frequently co-infected with rotavirus (28.6%) or G. lamblia (24.5%).

Etiology of acute diarrhea among United States military personnel deployed to South America and west Africa

A study of acute diarrhea was conducted from 1985 to 1987 among U.S. military personnel participating in routine shipboard exercises in South America and West Africa and ground troops deployed to coastal Ecuador. An enteropathogen was identified in 146 (51%) of 289 acute cases of diarrhea. Enterotoxigenic Escherichia coli, found in 50 (17%) patients with diarrhea, was the most commonly identified enteropathogen. Viral enteropathogens were also found in a high percentage of acute cases of diarrhea: rotavirus was detected in 11% of the patients and Norwalk virus infection in 10%. Most enteric pathogens were acquired in equal frequencies in South America and West Africa, except for rotavirus infection which was identified more often in West Africa and enteroaggregative E. coli infection which was identified more often in South America. Bacterial enteropathogens were frequently resistant to trimethoprim/sulfamethoxazole, but no resistance to quinolone drugs was observed, indicating that quinolone drugs have become important agents for the treatment of diarrhea in South America and West Africa.

Norfloxacin compared to trimethoprim/sulfamethoxazole for the treatment of travelers' diarrhea among U.S. military personnel deployed to South America and West Africa

A randomized treatment trial of travelers' diarrhea was carried out among U.S. military personnel participating in routine exercises in several port cities in South America and West Africa. A 5-day, twice daily course of either norfloxacin (400 mg) or trimethoprim/sulfamethoxazole (TMP/SMX, 160/800 mg) was given to 142 volunteers. At the end of 5 days of treatment, diarrhea had resolved in 100% of 73 patients receiving norfloxacin and 97.1% (67/69) receiving TMP/SMX. A probable bacterial pathogen was determined in 44% of 142 subjects: 49% of the norfloxacin group and 39% of the TMP/SMX group. The most common pathogens detected were enterotoxigenic Escherichia coli in 20% of cases and rotavirus in 15%. Resistance to TMP/SMX was present in 20 (27%) bacterial isolates, while no resistance to norfloxacin was found. Eight of 10 patients in the TMP/SMX treatment group who had TMP/SMX-resistant bacterial enteropathogens improved clinically. Both norfloxacin and TMP/SMX were clinically effective in the treatment of travelers' diarrhea in this military population.

Diarrheal disease during Operation Desert Shield

BACKGROUND

Under combat conditions infectious disease can become a major threat to military forces. During Operation Desert Shield, there were numerous outbreaks of diarrhea among the U.S. forces. To evaluate the causes of and risk factors for diarrheal disease, we collected clinical and epidemiologic data from U.S. troops stationed in northeastern Saudi Arabia.

METHODS

Between September and December 1990, stool cultures for enteric pathogens were obtained from 432 military personnel who presented with diarrhea, cramps, vomiting, or hematochezia. In addition, a questionnaire was administered to 2022 soldiers in U.S. military units located in various regions of Saudi Arabia.

RESULTS

A bacterial enteric pathogen was identified in 49.5 percent of the troops with gastroenteritis. Enterotoxigenic Escherichia coli and Shigella sonnei were the most common bacterial pathogens. Of 125 E. coli infections, 39 percent were resistant to trimethoprim-sulfamethoxazole, 63 percent to tetracycline, and 48 percent to ampicillin. Of 113 shigella infections, 85 percent were resistant to trimethoprim-sulfamethoxazole, 68 percent to tetracycline, and 21 percent to ampicillin. All bacterial isolates were sensitive to norfloxacin and ciprofloxacin. After an average of two months in Saudi Arabia, 57 percent of the surveyed troops had at least one episode of diarrhea, and 20 percent reported that they were temporarily unable to carry out their duties because of diarrheal symptoms. Vomiting was infrequently reported as a primary symptom, but of 11 military personnel in whom vomiting was a major symptom, 9 (82 percent) had serologic evidence of infection with the Norwalk virus.

CONCLUSIONS

Gastroenteritis caused by enterotoxigenic E. coli and shigella resistant to a number of drugs was a major problem that frequently interfered with the duties of U.S. troops during Operation Desert Shield.

Diarrhea and intestinal invasiveness of Aeromonas strains in the removable intestinal tie rabbit model

Twelve Aeromonas strains were tested for virulence by using the removable intestinal tie adult rabbit diarrhea model. Mortality was 50% or greater for 7 of 12 strains; 23 of 37 rabbits that died developed diarrhea before death, and 11 of 27 surviving rabbits developed diarrhea. Aeromonas bacteremia was detected in 36 of 37 (97%) animals that died, but only in 2 of 27 (7%) survivors. Death, diarrhea, and bacteremia were all strongly strain dependent. Gastrointestinal lesions varied from moderate focal enteritis to severe multifocal necrosis and hemorrhage of the ileal mucosa, often accompanied by hepatic and splenic lesions. Intestinal colonization assays performed after infection indicated that the ileum was the most heavily colonized portion of the gut and the probable site of invasion. The application of the removable intestinal tie adult rabbit diarrhea model for intestinal challenge with Aeromonas strains has shown that some isolates are capable of invading the mucosa of rabbits, causing diarrhea and bacteremia. These data suggest that such strains may be important in causing human invasive diarrhea.

Penicillinase-producing Neisseria gonorrhoeae in various seaport cities of Latin America

One hundred fifteen acute cases of gonorrhea were documented in U.S. military personnel during a five-month cruise in which 22 port cities of Latin America were visited in 1985. Penicillinase-producing Neisseria gonorrhoeae (PPNG) was isolated from 23 (20%) of the 115 cases. No penicillin-resistant, beta-lactamase-negative gonococci were encountered. None of the ten cases of gonorrhea acquired in the Caribbean region was due to PPNG. In South America, the PPNG infection rate was 35% (19/54) in ports along the Pacific Ocean and 8% (4/51) in those along the Atlantic. Infections incurred in four cities of three countries on the Pacific coast of the South American continent accounted for 78% of all PPNG isolates. Although the study did not deal directly with infections in the local populations, the data suggest that PPNG are common in coastal South America and that hyperendemic foci exist in some cities of the continent's western coast.

Mucosal and systemic immunity to Campylobacter jejuni in rabbits after gastric inoculation

The mucosal and systemic immune responses to Campylobacter jejuni were studied in rabbits receiving gastric inoculation with live organisms. A lavage procedure was used to facilitate repeated monitoring of the intestinal immune response to C. jejuni. Immunity to C. jejuni was determined by secondary challenge by using the removable intestinal tie adult rabbit diarrhea (RITARD) model and monitoring for resistance to colonization and bacteremia. Oral-gastric inoculation of normal rabbits produced a transient intestinal colonization without diarrhea. C. jejuni serotypes differed in their ability to colonize the intestines of rabbits and to stimulate primary intestinal and serum antibody responses. Animals previously colonized were resistant to recolonization and the development of bacteremia after homologous challenge by the RITARD procedure but were not resistant to heterologous challenges. Anticampylobacter intestinal and serum IgA titers before this secondary infection were the most reliable predictors of resistance to colonization and bacteremia.

Alkaline phosphatase-conjugated oligonucleotide probes for enterotoxigenic Escherichia coli in travelers to South America and West Africa

Several studies have demonstrated the usefulness of 32P-labeled recombinant DNA probes for identifying enterotoxigenic Escherichia coli (ETEC). The use of radioisotopes and X-ray development, however, severely handicaps the utility of DNA probes in most clinical laboratories. In this study, enzyme-labeled oligonucleotide probes for ETEC LT (heat-labile toxin) and ST (heat-stable toxin) genes were compared with the standard Y1 adrenal cell and suckling mouse assays for their ability to identify ETEC in a population of American adults experiencing acute episodes of diarrhea in South America and West Africa. The LT probe hybridized with 12% (64 of 529) of the E. coli colonies tested, whereas 11% (57 of 529) were positive by Y1 adrenal cell assay. DNA from 9% (47 of 529) of the E. coli colonies tested hybridized with the ST probe, whereas only 5% (28 of 529) produced ST as measured by the suckling mouse bioassay. For the patient samples tested, correlation between probe and bioassay for LT was 97%, or three discrepancies in 111 patients tested. Overall concordance of the ST probe and bioassay was 95%, or five discrepancies in 111 patients. Enzyme-labeled oligonucleotide probes represent a major advance in the diagnosis of ETEC-associated diarrheal disease and may be used in laboratories with minimal equipment.

Empirical treatment of Shigella dysentery with trimethoprim: five-day course vs. single dose

Fifty-three adults hospitalized with Shigella dysentery were empirically treated with trimethoprim (200 mg) twice/day for 5 days, a single dose of trimethoprim (600 mg), or placebo in a randomized double-blind trial. During the first 24 hr of therapy, there was a reduction in the number of stools in 18/21 (86%) of patients treated with the 5-day regimen (trimethoprim-5) and 13/15 (87%) of patients treated with a single dose (trimethoprim-1), compared with 7/17 (41%) of the placebo group (P less than 0.025, both comparisons). The mean number of stools passed in the first 24 hr of therapy was 10.6, 10.8, and 21.3 stools in the trimethoprim-5, trimethoprim-1, and placebo groups, respectively. The mean (+/- SD) change in number of stools from baseline among treated patients during the first 24 hr was -4.9 (6.6) and -6.3 (6.3) for the trimethoprim-5 and trimethoprim-1 groups, respectively, compared with an increase of +2.4 (14.8) for the placebo group. There was a clinical failure at 48 hr in 9% of the trimethoprim-5 patients and 13% of trimethoprim-1 patients compared with 70% of placebo patients (P less than 0.005, both comparisons). Although we were unable to demonstrate a difference in efficacy between the two dosage schedules of trimethoprim, we conclude that both treatment regimens are effective for the treatment of Shigella dysentery.

Gastric lavage: a simple method to obtain IgA-rich intestinal secretions from the rabbit

A lavage procedure was developed to obtain intestinal secretions from rabbits. The procedure facilitated the repeated monitoring of the intestinal IgA immune response of these animals to enteric infection with Campylobacter jejuni. This non-invasive technique was easily performed, reproducible and yielded consistent levels of IgA from rabbit intestinal secretions. It is anticipated that this procedure will aid in the study of the intestinal immune response of rabbits to other enteric pathogens.

In vitro activity of ciprofloxacin compared to trimethoprim-sulfamethoxazole against Campylobacter spp., Shigella spp. and Enterotoxigenic Escherichia coli causing travellers' diarrhea in Egypt

The in vitro activity of ciprofloxacin against bacterial enteropathogens isolated from cases of travellers' diarrhea in Egypt was compared to trimethoprim (TMP) and trimethoprim-sulfamethoxazole (SXT). No resistance to ciprofloxacin was noted for any of the Campylobacter jejuni/coli, Shigella spp., and enterotoxigenic Escherichia coli strains examined. However, resistance to TMP and SXT was noted among these same strains. Because of its broad spectrum and lack of resistance, ciprofloxacin is potentially a useful drug for the treatment of diarrhea caused by bacterial enteropathogens encountered in this region of the world.

Evaluation of febrile patients in Port Sudan, Sudan: isolation of dengue virus

One hundred consecutive patients admitted to the Port Sudan Hospital with a temperature greater than or equal to 100 degrees F were evaluated. Enteric fever was diagnosed in 19 patients and malaria in 13. Virologic studies identified 21 cases of dengue infection. One dengue 1 and 17 dengue 2 infections were diagnosed by viral isolation. Three untyped dengue infections were identified serologically. The clinical presentation and course of patients infected with dengue virus were most consistent with classic dengue fever. There was no evidence of hemorrhagic phenomena or shock in any of the dengue-infected patients. Both dengue 1 and 2 must be considered causes of acute fever in East Africa.

Population indices of chiggers (Leptotrombidium deliense) and incidence of scrub typhus in Chinese military personnel, Pescadores Islands of Taiwan, 1976-77

Larval Leptotrombidium deliense were recovered from live-trapped Suncus murinus, Rattus rattus and R. norvegicus captured in the Pescadores Islands of Taiwan during 1976 and 1977. Weekly and monthly indices of chigger infestation expressed as a percentage of hosts infested and the number of chiggers per host for S. murinus and Rattus spp. were calculated. Close correlations were observed between monthly indices of L. deliense measured for S. murinus and Rattus spp. and the number of laboratory-confirmed cases of scrub typhus per month. Weekly indices from S. murinus correlated more closely with number of cases than did weekly indices from Rattus spp. The critical level of chigger infestation necessary for a single case of scrub typhus in a month was estimated at 0.69 chigger per S. murinus and 0.68 chigger per Rattus spp. The weekly index of chigger infestation necessary for a single case of scrub typhus during a week was calculated at 0.47 chiggers per shrew. Critical levels of chigger infestations expressed as percentages of hosts infested were not calculated.

Cell wall modification resulting from in vitro induction of L-phase variants of Nocardia asteroides

The chemical composition of the cell walls of several L-form revertants derived from Nocardia asteroides 10905 was determined at different stages of growth. It was observed that each L-form revertant had a cell well that differed from that of the parental strain when grown under identical conditions. In some strains the peptidolipid and mycolic acid components were affected the most, whereas in other strains the fatty acid, sugar, and mycolic acid moieties were altered. Shifts in mycolic acid size were prominent, whereas the basic peptidoglycan structure appeared to be affected the least. Both the method used to induce the L-form of N. asteroides 10905 and the length of time these organisms were maintained in the wall-less state affected the degree of cell wall modification during the reversion process. Thus, removal of the cell wall appeared to potentiate and select for mutational alterations within the cell envelope of N. asteroides, and these changes resulted in altered cellular and colonial morphology.

Identification of mosquito blood meals by cellulose acetate and starch gel electrophoresis

Cellulose acetate (CAE) and starch gel electrophoresis (SGE) were examined for their ability to identify species hemoglobins in mosquito blood meals. Blood meals analyzed serologically by the precipitin (PT) and passive hemagglutination inhibition (PHI) techniques served as standards for comparison. CAE, could not differentiate blood meals from divergent vertebrate hosts (man, rabbits, and mice) solely on the basis of the migratory properties of their respective hemoglobins. However, all could be differentiated when the migratory properties of both their hemoglobins and serum albumins were considered. CAE, like PT, was consistently able to identify blood meals for 18--24 hr post-ingestion. In contrast, PHI was able to identify blood meals for up to 48 hr post-feeding. SGE lacked the sensitivity of CAE, PHI and PT. SGE could only differentiate blood meals for 5--7 hr after ingestion. These results indicate that CAE has potential as a rapid technique for determining the origin of blood meals ingested by arthropod disease vectors.

Prevention of scrub typhus. Prophylactic administration of doxycycline in a randomized double blind trial

We conducted a prospective randomized double blind study on the effects of doxycycline as a prophylactic antibiotic against scrub typhus. A total of 1,125 military subjects was followed for periods as long as 5 months of exposure in a hyperendemic focus in the Pescadores Islands of Taiwan. Oral 200 mg doses of doxycycline (Vibramycin) or placebo were given once each week throughout the trial. The incidence rate of scrub typhus in the placebo group was 2.5 times greater than that of the group taking doxycycline (P = 0.11). When subjects who failed to comply with scheduled administration of doxycycline were removed from the analysis, the incidence rate of scrub typhus in the control group was five times greater than that in the drug group (P = 0.04). The rates of infection with Rickettsia tsutsugamushi and of sick call reports were the same in experimental and control groups. The drug was well tolerated in pretrial tests and complaints were negligible during the conduct of the trial. Doxycycline appears to be an excellent antibiotic for the prevention of scrub typhus among personnel exposed to high risk of infection with R. tsutsugamushi.

In vitro stimulation of human peripheral blood lymphocytes by soluble and membrane fractions of renografin-purified typhus group rickettsiae

Cell-free extracts of disrupted Renografin-purified Rickettsia typhi and R. prowazekii were evaluated as antigens in lymphocyte transformation assays for cell-mediated immunity to typhus group rickettsiae in 19 individuals with and 9 without histories of exposure to these organisms. Exposure consisted of clinical disease, vaccination with epidemic typhus vaccine, or occupational exposure to these agents. Both the soluble and membrane fractions of disrupted purified rickettsiae were used, and transformation of peripheral blood lymphocytes (PBL) was determined in microcultures by incorporation of [(3)]thymidine. Of the antigen concentrations tested (1 to 400 mug/ml), 10mug/ml appeared to be the most satisfactory. At this concentration, PBL transformation was highly reproducible and correlated well with donor exposure and the presence of enzyme-linked immunosorbent assay anti-typhus group immunoglobulin G. At higher concentrations, PBL from both exposed and control donors often responded to a lipopolysaccharide-like component present in these preparations. Specific transformation responses to rickettsial fractions were detected in several individuals decades after infection or vaccination, indicating that both fractions contained antigens associated with persisting cell-mediated immunity in humans. Generally, stimulation indexes with the soluble fraction were slightly greater than those obtained with corresponding concentrations of the membrane preparation, and in three individuals transformation was observed only with the soluble fraction. PBL transformation to soluble fractions also appeared to have some species specificity, since PBL from individuals with documented R. typhi infections were more responsive to the homologous soluble preparation than to the soluble fraction of R. prowazekii. PBL transformation also correlated well with homologous but only poorly with heterologous enzyme-linked immunosorbent assay immunoglobulin G titers.