A clinico-epidemiological study of epidemic typhus in Africa.

Epidemic, louse-borne typhus persists in the rugged, mountainous areas of Ethiopia and much of northeastern and central Africa as well as in the rural highlands of Central and South America, where the conditions of living favor the harboring of body lice and where antibiotic treatment and effective louse-control measures are unavailable. The historical significance and current epidemiology of typhus, including the reservoir of Rickettsia prowazekii in flying squirrels in the United States, are reviewed, and the clinical presentation, laboratory findings, and hospital course in the cases of 60 patients admitted with epidemic, louse-borne typhus to the St. Paul's Hospital in Addis Ababa, Ethiopia, are described. Treatment of this disease with oral doxycycline, tetracycline, or chloramphenicol prevents complications and results in prompt resolution of symptoms.

Cell-mediated immune responses of adults to vaccination, challenge with Rickettsia rickettsii, or both.

As a part of a study to evaluate a formalin-killed Rickettsia rickettsii vaccine, lymphoproliferative (LT) and delayed-type hypersensitivity (DTH) skin test responses to killed R. rickettsii were measured as correlates of cell-mediated immunity in volunteers who were vaccinated, challenged with R. rickettsii, or both. We detected LT responses in 26 (51%) of 51 volunteers after vaccination. After challenge, six of six unvaccinated volunteers and 12 of 16 vaccinated volunteers developed Rocky Mountain spotted fever (RMSF); all 22 mounted LT responses. The vaccinated individuals developed LT responses of greater magnitude and 1-2 weeks earlier than unimmunized controls (41,049 versus 15,084 mean net counts per minute [cpm]), suggesting that vaccination primed the cellular immune system. Moreover, development of LT responses postvaccination was associated with the amelioration of RMSF, as indicated by a slightly longer mean incubation period (328 hr versus 302 hr) and a shorter illness (19 hr versus 26 hr) in LT responders than in LT nonresponders. However, the postvaccination LT response did not discriminate between vaccinated individuals who resisted challenge and those who did not. Skin tests using killed R. rickettsii as antigen, performed in volunteers 14-17 months postvaccination or 12-15 months after challenge, revealed a weak but significant reaction in 50% of those who had received vaccine only, and a moderately strong reaction in all vaccinated and unvaccinated volunteers who had been challenged with R. rickettsii. The relationships between induction of protective immunity against intracellular bacteria by killed and replicating organisms and LT and DTH responses are discussed.

Preliminary characterization of inflammatory infiltrates in response to Rickettsia prowazekii reinfection in man: immunohistology.

The local perivascular mononuclear cell inflammatory infiltrate (PVI) response to intradermal (ID) challenge with viable R. prowazekii was studied in a typhus-immune subject. An immunohistochemical method for specific mononuclear cell markers was used on skin punch biopsies taken 6, 24 and 48 hr after challenge. By 24 to 48 hr, the histologic findings were consistent with a delayed-type hypersensitivity reaction (DTHR). Both CD4+ and CD8+ T lymphocytes dominated the PVI at 48 h. CD8+ cells entered the PVI more rapidly than CD4+ cells. Local control of R. prowazekii challenge in an immune human subject was associated with recruitment into the PVI of T lymphocytes which are rich sources of gamma-interferon, and CD8+ T cells which are potentially cytotoxic for R. typhi-infected cells.

Ultrastructural morphology of the lung in cystic fibrosis.

Cystic fibrosis (CF) is the most common lethal genetic disease among Caucasians, with much of the morbidity and most of the mortality related to pulmonary complications. The underlying defect in this disease has yet to be precisely defined, so it is somewhat surprising that a comprehensive study of the ultrastructural morphology of the lung in CF has not heretofore been reported. We used transmission electron microscopy to examine the small airways in 15 patients who had died of CF, and compared the findings with 15 disease controls with non-CF chronic airways disease and 15 patients with normal lung morphology. The lung parenchyma was also examined ultrastructurally in 7 patients with CF, 4 disease controls, and 4 normal lung cases. In addition, the literature regarding the ultrastructural morphology of the large airways in CF was reviewed. Patients with CF showed non-specific ciliary abnormalities, hyperplasia of mucous cells, increased numbers of pulmonary neuroendocrine and indeterminate cells, degeneration and sloughing of epithelial cells, and colonization of bacteria of the mucous layer of the small airways when compared with normal controls. Alveoli showed non-specific injury and regeneration of type II pneumocytes. However, these changes were all similar to those observed in the disease controls. Specifically, no cellular or subcellular ultrastructural abnormality unique to CF was observed. It is probable that the most useful ultrastructural approach to the lung in CF in future studies will involve X-ray microanalytical studies of ionic composition using cryotechniques.

Newborn rats in the murine typhus enzootic infection cycle: studies on transplacental infection and passively acquired maternal antirickettsial antibodies.

This study focused attention on the newborn rat as a possible significant participant in the highly successful enzootic cycle of murine typhus. We examined the influence of maternal Rickettsia typhi (R. mooseri) infection in rats on the offspring with respect to the possible vertical transmission of R. typhi and the passive transfer of maternal antirickettsial antibodies. Transmission of R. typhi by rickettsemic pregnant rats did not occur either transplacentally during gestation to their fetuses or postnatally through colostrum and milk to their newborn. The rickettsial burden of the placenta was sometimes greater than 10(6) plaque forming units per g tissue and undetectable in colostrum or milk. However, newborn rats were highly susceptible to infection per os. Transplacental passage of antirickettsial antibody to offspring was detectable only when the mother's antibody titer was high. Passive postpartum acquisition of antirickettsial antibodies by newborn rats from colostrum and milk of immune mothers occurred regardless of the height of the maternal antibody titer, rose to a maximum at about 3 weeks of age, and then declined rapidly, becoming undetectable 4 weeks after birth.

Selected observations on rickettsiae and their host cells.

The study of the interaction between rickettsiae and their host cells is in its infancy. Members of the genera Rickettsia, Coxiella and Rochalimaea show considerable diversity in host cell range (in vivo vs. in vitro), kind of association with host cell (pericellular, intracellular), mode of entry, interactions with various host cell membranes, intracellular localization (intraphagosomal, free in cytoplasm, intranuclear), adaptation to preferred microhabitat (e.g., optimal pH for enzymes), details of growth cycle, mechanisms of host cell damage. Quantitative in vitro methods exist for the study of infection cycles. Knowledge of nutritional requirements is almost non-existent. Host factors, (e.g., antibody, lymphokines, immune interferon) influence intracellular rickettsiae. Rickettsia-host cell interactions remain a fertile field for discovery.

[Serological approach to the occurrence of rickettsioses in the Central African Republic]. / Approche sérologique sur l'incidence des rickettsioses en République Centrafricaine.

A serosurvey for evidence of human rickettsial infections was carried out in the Republic of Central Africa on 144 sera by indirect immunofluorescence (IIF) and microagglutination tests (MA). There was no serological evidence of epidemic typhus and only two sera were positive for murine typhus. Approximately 15% of the surveyed population was serologically positive by MA for R. conorii antibodies. However, 48% of this population had spotted fever group antibodies as detected by IIF but were negative in MA for R. conorii, R. rickettsii and R. akari antibodies. These sera with high titers in IIF and negative in MA lead us to believe that in Central Africa there are rickettsiae pathogenic for man that are related to the Spotted Fever group and are yet to be identified.

Experimental infection with Rickettsia mooseri and antibody response of adult and newborn laboratory rats.

Quantitative studies of selected features of peripherally induced Rickettsia mooseri (= R. typhi) infection in Rattus norvegicus-derived white laboratory rats revealed a unique association between microbe and amplifying vertebrate host which appears to be especially conducive to maintenance of the enzootic cycle. Both adult and newborn (1-3 days old) rats were highly susceptible to percutaneous infection (ID50 = approximately 1 organism), but neither showed signs of disease or died even when inoculated with 10(4)-10(5) plaque-forming units. Gain in body weight of infected newborn rats was indistinguishable from that of uninfected newborn rats over the first 3 weeks of life. The course of the systemic infection, as measured by the rise and fall of R. mooseri titers in blood, brain and kidney and the serum antibody response, was almost identical in adult and newborn rats. Thus, despite their immaturity in certain immunological processes, newborn rats controlled postnatal R. mooseri infection about as well as did adult rats. The rickettsemic period of about 10 days corresponds to the period of infectivity of inoculated rats for fleas. Rickettsiae were not isolated from blood, brain or kidneys by methods employed for more than 4-5 weeks after infection. Serum antirickettsial antibodies persisted for at least 60 weeks postinfection, i.e., longer than the usual life span of rats in nature and, hence, are a valid measure of the cumulative experience of rat populations with R. mooseri infection.

Antibiotic susceptibility patterns in Rochalimaea quintana, the agent of trench fever.

Rochalimaea quintana, the etiological agent of trench fever, was tested by an agar dilution method for its susceptibility to the following 14 antibiotics: penicillin G, methicillin, ampicillin, cephalothin, vancomycin, doxycycline, tetracycline, erythromycin, chloramphenicol, streptomycin, kanamycin, rifampin, colistin, and amphotericin B. The MIC of each of these antibiotics was determined. The results showed that R. quintana is susceptible in vitro to these antibiotics, with the exception of vancomycin, kanamycin, streptomycin, colistin, and amphotericin B.

Characteristics of lymphoid cells that adoptively transfer immunity to Rickettsia mooseri infection in mice.

The capacity of adoptively transferred immune lymphoid cells or passively transferred immune serum to alter the course of an established Rickettsia mooseri (R. typhi) infection in the spleen was evaluated in BALB/c mice. Immune cells, but not immune serum, controlled the established infection. An effective lymphocyte was a T-cell which had to possess a capacity to divide.

Characteristics of Rickettsia mooseri infection of normal and immune mice.

Rickettsia mooseri infection initiated by subcutaneous injection has been studied in BALB/c mice with the objective of developing a model for the study of immune mechanisms. Characterization of infection included the following: measurement of the replication, dissemination, and clearance of rickettsiae; measurement of correlates of the immune response, including humoral antibody, hypersensitivity to subcutaneously inoculated rickettsial antigen, and activation of nonspecific macrophage microbicidal capacity; and measurement of resistance to a second homologous challenge. Local infection at the site of subcutaneous injection progressed through day 5 and was controlled by day 7. Systemic infection as determined by the presence of rickettsiae in spleen was first detected on day 7 and progressed through day 14; however, rickettsiae persisted in this organ at reduced numbers through at least day 28. Control of the local infection at the site of subcutaneous injection occurred at about the time humoral antibodies and hypersensitivity reactions to subcutaneously injected rickettsial antigens became demonstrable and was paralleled by a capacity to resist homologous subcutaneous challenge at a site distant from that of the primary infection. Systemic infection progressed in spite of this acquired immune capacity and was controlled in the spleen in parallel with the development of enhanced macrophage microbicidal capacity in the liver. The results show that an acquired immunity is capable of restricting rickettsial growth at subcutaneous sites at a time when rickettsiae are increasing in titer in deep organs.

Scanning electron microscopic study of the airways in normal children and in patients with cystic fibrosis and other lung diseases.

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine pulmonary tissue from 9 patients with cystic fibrosis (CF), 12 patients with diseases other than CF, and from two surgically resected specimens with no known airways disease. A region of the human airways, the transition zone, was observed between the end of the terminal bronchiole and the type II alveolar cell lining of the respiratory bronchioles. This region was lined predominantly by nonciliated bronchiolar (NCB) cells. Patients with CF exhibited indistinct transition zones, epidermoid metaplasia, large dilated bronchial glands, copious surface mucus, alveolar destruction, and unusual microvilli; no single lesion specific for cystic fibrosis was identified.

Rickettsia mooseri infection in the fleas Leptopsylla segnis and Xenopsylla cheopis.

Detailed observations on the acquisition and propagation of experimental Rickettsia mooseri infection in two species of fleas are presented. Rickettsia mooseri infection became detectable by means of the direct fluorescent antibody test about 2 days earlier in Leptopsylla segnis than in the putative vector, Xenopsylla cheopis. By the 6th day after the infective feeding, the entire lining and the lumen of the midgut in L. segnis contained masses of rickettsiae and the agent was being passed in the feces of the flea, whereas in X. cheopis these events did not occur until the 8th day. Basic behavioral differences in the two species of flea may explain these discrepancies and also influence their ability to serve as vectors of murine typhus. As a semisessile flea and sustained feeder, L. segnis only rarely attaches to a second individual and thus has an opportunity to acquire a heavy dose of rickettsiae, if feeding on a rickettsemic host. X. cheopis, in contrast, feeds rapidly and intermittently, even on man, and generally leaves its host soon thereafter, later returning to the same or another host to feed again. While L. segnis may not be as efficient a vector as X. cheopis regarding the intramurine cycle or transmission to man of murine typhus, the dense accumulation of infective feces on certain sites on the fur of the host raises the possibility of air-borne infection to man or rodent. Infection with R. mooseri had no effect on the survival of X. cheopis and L. segnis. Furthermore, no visible cytopathological effect was found in the paraffin-embedded sections of infected fleas.(ABSTRACT TRUNCATED AT 250 WORDS)

Serodiagnosis of Rocky Mountain spotted fever: comparison of IgM and IgG enzyme-linked immunosorbent assays and indirect fluorescent antibody test.

To characterize IgM and IgG antibody responses in Rocky Mountain spotted fever (RMSF), a microtiter enzyme-linked immunosorbent assay (ELISA) using density gradient-purified Rickettsia rickettsii as antigen was developed. Sera of vaccinated individuals and patients with RMSF were tested by ELISA and by indirect fluorescent antibody (IFA) tests. Diagnostic agreement between ELISA and the IFA test was 76% and 52% for IgG and IgM antibody, respectively. Diagnostic agreement between the ELISA for IgG antibody and the IFA test for total immunoglobulins was 84%. The ELISAs for IgM and IgG antibody were as specific (100%) and as sensitive (100%) as the IFA test (83%-100%) in detecting antibody increases in paired sera from persons with RMSF and were superior to the IFA test in detecting seroconversions in vaccinees. The ELISA also detected antibodies in a single convalescent-phase serum with sensitivity and reliability. The ELISA for IgG antibody is appropriate for seroepidemiology and serodiagnosis since it permits measurement of antibody at a single dilution of serum up to a year after illness.

Reactogenicity, immunogenicity, and efficacy of a chick embryo cell-derived vaccine for Rocky Mountain spotted fever.

A new formalin-inactivated vaccine prepared by sucrose density gradient centrifugation of tissue culture-grown Rickettsia rickettsii was evaluated for safety and immunogenicity in a placebo-controlled, double-blind study. Most of the 52 seronegative adult vaccinees, 88% after the first and 66% after the second dose, experienced brief, mild (mostly local) reactions, but only 50% exhibited a systemic immune response to vaccination. Six unvaccinated volunteers (controls) and 16 of these vaccinees were challenged with R rickettsii one month after vaccination. Vaccine efficacy was 25%; all six controls and 12 of 16 vaccinees developed typical Rocky Mountain spotted fever. The incubation period was longer, the duration of constitutional symptoms shorter, and the height of fever lower in ill vaccinees than in controls. The vaccine provided only partial protection against Rocky Mountain spotted fever but ameliorated the illness.

Interferonlike factors from antigen- and mitogen-stimulated human leukocytes with antirickettsial and cytolytic actions on Rickettsia prowazekii. Infected human endothelial cells, fibroblasts, and macrophages.

Unique features of the primary site of rickettsial replication in typhus fevers, i.e., within the endothelial cells of small blood vessels in tissues, suggest that effector mechanisms, other than those dependent on phagocytosis by activated macrophages with enhanced microbicidal properties, most likely are necessary to explain the cell-mediated immune control of intracellular rickettsial replication in these sites. Theoretically, such mechanisms might involve contact between infected endothelial cells and activated T lymphocyte subpopulations or macrophages or immunologically induced soluble factors or lymphokines. Support for the existence of at least one of these alternative effector mechanisms is presented here for Rickettsia prowazekii. Cultures of human blood leukocytes, upon immunologically specific stimulation with R. prowazekii antigen or nonspecific stimulation with the mitogen phytohemagglutinin, produce soluble factor(s) in the supernatant fluid which, in culture, have (a) an intracellular antirickettsial action on R. prowazekii-infected human endothelial cells, fibroblasts, and macrophages, and (b) a specific cytolytic action on R. prowazekii-infected, but not uninfected bystander, human fibroblasts. Neither action is demonstrable in R. prowazekii-infected chicken embryo fibroblasts. The factor(s) has no direct antimicrobial action on extracellular rickettsiae and is inactivated by heating at 56 degree C for 1 h or by acid treatment at pH 2. Expression of the antirickettsial action requires new host cell messenger transcription and protein synthesis, whereas the cytolytic action does not. The circumstances of production and action and the properties of the factor(s) responsible for the intracellular antirickettsial, and perhaps also the cytolytic action are consistent with those of immune interferon (IFN-gamma).

Penicillin-induced unstable intracellular formation of spheroplasts by rickettsiae.

Penicillin G (greater than or equal to 20 micrograms/ml) is rapidly rickettsiacidal for intracellular Rickettsia prowazekii. Light and electron microscopic examinations revealed that penicillin G in culture medium induced a predictable transformation into typical enlarging spheroplasts deficient in the internal, putative peptidoglycan layer of the outer membrane. Under certain conditions, spheroplasts ruptured to discharge contents into host cell cytoplasm and to leave empty shells of defective outer membrane and diffuse amorphous intracytoplasmic antigen. Host cell destruction often accompanied spheroplast rupture. Penicillin G (100 micrograms/ml) caused similar spheroplast formation by Rickettsia rickettsii, but 1,000 micrograms/ml caused neither growth inhibition nor spheroplast formation in Rickettsia tsutsugamushi. The clinical and epidemiological significance of a practical rickettsiacidal drug for the treatment of louse-borne typhus fever is discussed. Practical pharmacologic considerations preclude the use of penicillin for the treatment of typhus or spotted fever.