Epidemiology of murine typhus.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
A F Azad
Publications and source records attributed to A F Azad.
Quantitation of antisporozoite immunoglobulins in the hemolymph of Anopheles stephensi after bloodfeeding.
Passage of rat antibodies induced by Plasmodium falciparum circumsporozoite protein (anti-CS IgG) from the bloodmeal into the hemocoel of uninfected Anopheles stephensi mosquitoes was quantified using enzyme-linked immunosorbent assay (ELISA) techniques. Anti-CS IgG were present in hemolymph immediately upon cessation of mosquito feeding. Titers peaked at 3 hr post-ingestion then declined steadily, becoming negligible at 18 hr. Substantial titers were present in the bloodmeal at 24 hr post-ingestion. By 48 hr, anti-CS IgG in both mosquito hemolymph and bloodmeal were virtually absent. Estimated quantities of anti-CS IgG in the hemolymph at 3 hr post-ingestion were 905-958 ng/ml, representing approximately 0.5% of that present in the host serum. Rat IgG subclasses 1, 2a, and 2b passed into hemolymph more readily than did IgM and possibly IgG2c. Hemolymph volume of unengorged mosquitoes (0.53 microliters) increased after a bloodmeal (0.73 microliters at 3 hr post-ingestion), suggesting that anti-CS IgG may move into the hemocoel in an aqueous solution.
Animals↗
Infection of colonized cat fleas, Ctenocephalides felis (Bouché), with a rickettsia-like microorganism.
We report the ultrastructure of a rickettsia-like microorganism in a colonized population of the cat flea Ctenocephalides felis (Bouché). The microorganism occurs principally in the cytoplasm of midgut cells, but similar microorganisms were detected in the tracheal matrix, muscle, hypodermis, ovaries, and the epithelial sheath of the testes. The microorganism has a well-defined cell membrane consistent with rickettsia and measures 0.25-0.45 microns in diameter with lengths up to 1.5 microns. It was observed repeatedly in fleas of 1 laboratory colony, including newly emerged non-bloodfed specimens, but not in specimens from several other sources.
Alphaproteobacteria↗
Rat leucocyte response to the bites of rat fleas (Siphonaptera: Pulicidae).
The host response to bites of the oriental rat flea, Xenopyslla cheopis Rothschild, was investigated by examining rat blood leucocyte kinetics, histopathology, and the effect that the host response had upon subsequent flea feeding and longevity. Test rats were subjected to controlled exposures of fleas, and leucocyte data from test rats were compared to those of unexposed controls. Of the five leucocyte types examined, only the basophil appeared to play a role in the host blood response to flea bites. Significant increases in blood basophil levels occurred 2-3 d after exposure but subsided to control levels within a week. However, flea feeding did not produce histopathology at the flea feeding sites nor did the basophilic blood response of rats affect subsequent feeding or longevity of the fleas.
Animals↗
Experimental transmission of murine typhus by Xenopsylla cheopis flea bites.
Transmission of Rickettsia typhi to rats by the bites of Xenopsylla cheopis (Rothschild) fleas was investigated. Procedures rigorously excluded the possibility of contamination of the host skin by flea faeces. Fleas with R. typhi infection (21-25 days post-infection) which fed through bolting cloth (45 min exposure to ten fleas) transmitted rickettsiae with a success rate of 20%. Infective fleas allowed free access to their host for 8 h (10-15 fleas/rat) gave transmission rates of 45-68%. They were also capable of inoculating R. typhi through a membrane of rat skin on a feeder. Only fleas which had been infected for 21 days or longer transmitted R. typhi orally. Oral transmission appeared to be the result of regurgitation of rickettsiae present in the foregut lumen rather than through salivary secretions.
Animals↗
Detection of murine typhus infected fleas with an enzyme-linked immunosorbent assay.
An enzyme-linked immunosorbent assay (ELISA) for the detection of Rickettsia typhi antigen in homogenates of pooled or individual laboratory infected fleas is described. The assay uses a double sandwich technique, employing a pool of monoclonal antibodies to capture the antigen and a hyperimmune rabbit serum for antigen detection. Using pools of R. typhi infected Xenopsylla cheopis, Ctenocephalides felis, and Leptopsylla segnis, the sensitivity of the ELISA was compared with direct fluorescent antibody examination of individual fleas for rickettsiae and with rickettsial titers determined by plaque enumeration on primary chicken embryo fibroblasts (PFU). Pooled samples with less than 4 PFU of viable rickettsiae gave ELISA results which were not significantly above background. Both ELISA OD and ELISA titer (last dilution giving an OD that was 2 SD above the control) of a 1:10 dilution of homogenate (4 fleas/ml) were linearly related to rickettsial titer up to 10(6.8) PFU/sample. Multiple freeze-thaws of pools of infected fleas led to a rapid loss of ELISA sensitivity. ELISA assays on single fleas demonstrated large individual variability in rickettsial content. This was independent of the number of days postinfectious feeding or the mean number of PFU/flea (10(1.7-6.9) found for pooled fleas in the same cohort. The sensitivity and ease of performance of ELISA should make it usable under field conditions.
Animals↗
Plasmodium falciparum: ingested anti-sporozoite antibodies affect sporogony in Anopheles stephensi mosquitoes.
In endemic areas, malaria-infected mosquitoes may feed upon humans who possess antibodies against malaria sporozoites. Therefore, we examined the effect that ingested anti-sporozoite antibodies have upon Plasmodium falciparum sporogony within Anopheles stephensi mosquitoes. Anti-sporozoite antibodies (IgG) traversed the midgut into the hemocoel within 3 hr following ingestion and, depending upon the titer, persisted for 6-24 hr. When fed to infected A. stephensi at 12 days postinfection (p.i.), anti-sporozoite antibodies bound to sporozoites in the hemocoel, but not to sporozoites residing in the salivary glands of the same mosquitoes. Anti-sporozoite antibodies also bound to developing oocysts when fed to infected A. stephensi at 5 days p.i. Oocysts in mosquitoes that had been fed anti-sporozoite antibodies on Day 5 p.i. produced significantly more sporozoites than did oocysts in nonimmune-fed (Day 5 p.i.) mosquitoes. In addition, the sporozoites from Day 5 immune-fed mosquitoes were significantly more infective to cultured human hepatoma cells than were sporozoites from nonimmune-fed controls. Use of hetereologous immune feedings at Day 5 p.i. did not result in an enhanced production of sporozoites, suggesting that enhancement is related to the specificity of the antibody and is not merely a nutritional effect.
Animals↗
Passage of host immunoglobulin G from blood meal into hemolymph of selected mosquito species (Diptera: Culicidae).
Explore the source record for details and available documents.
Animals↗
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.
Animals↗
Transmission of murine typhus rickettsiae by Leptopsylla segnis (Siphonaptera: Leptopsyllidae).
Explore the source record for details and available documents.
Animals↗
Suppression of Rickettsia typhi transmission in fleas maintained on murine typhus-immune rats.
The presence of host antibodies against Rickettsia typhi in the hemolymph of Xenopsylla cheopis fed on immune rats was studied using an indirect immunofluorescent antibody (IFA) test and enzyme-linked immunosorbent assay (ELISA). The time course experiment revealed that antibody to R. typhi appears in the flea hemolymph after 18 hr exposure to host and persists for 24 hr. IFA tests utilizing specific antisera to rat IgG (Fc) and rat IgG (Fab) fragments, indicate that some unaltered rat IgG to R. typhi were present in the hemolymph of immune fed fleas. Host antibody to R. typhi was detected on the surface of the rickettsiae in the flea hemolymph and gut contents by IFA. Maintenance of infected fleas on immune host had no significant effect on the establishment and subsequent growth of rickettsiae within the fleas. However, 19-22 day infected fleas maintained on immune hosts failed to transmit R. typhi to baby rats.
Animals↗
Flea-borne rickettsioses: ecologic considerations.
Ecologic and economic factors, as well as changes in human behavior, have resulted in the emergence of new and the reemergence of existing but forgotten infectious diseases during the past 20 years. Flea-borne disease organisms (e.g., Yersinia pestis, Rickettsia typhi, R. felis, and Bartonella henselae) are widely distributed throughout the world in endemic-disease foci, where components of the enzootic cycle are present. However, flea-borne diseases could reemerge in epidemic form because of changes in vector-host ecology due to environmental and human behavior modification. The changing ecology of murine typhus in southern California and Texas over the past 30 years is a good example of urban and suburban expansion affecting infectious disease outbreaks. In these areas, the classic rat-flea-rat cycle of R. typhi has been replaced by a peridomestic animal cycle involving, e.g., free-ranging cats, dogs, and opossums and their fleas. In addition to the vector-host components of the murine typhus cycle, we have uncovered a second typhuslike rickettsia, R. felis. This agent was identified from the blood of a hospitalized febrile patient and from opossums and their fleas. We reviewed the ecology of R. typhi and R. felis and present recent data relevant to the vector biology, immunology, and molecular characterization and phylogeny of flea-borne rickettsioses.
Animals↗
Rickettsial pathogens and their arthropod vectors.
Rickettsial diseases, important causes of illness and death worldwide, exist primarily in endemic and enzootic foci that occasionally give rise to sporadic or seasonal outbreaks. Rickettsial pathogens are highly specialized for obligate intracellular survival in both the vertebrate host and the invertebrate vector. While studies often focus primarily on the vertebrate host, the arthropod vector is often more important in the natural maintenance of the pathogen. Consequently, coevolution of rickettsiae with arthropods is responsible for many features of the host-pathogen relationship that are unique among arthropod-borne diseases, including efficient pathogen replication, long-term maintenance of infection, and transstadial and transovarial transmission. This article examines the common features of the host-pathogen relationship and of the arthropod vectors of the typhus and spotted fever group rickettsiae.
Animals↗