Complementary factors contributing to the rapid spread of HIV-I in sub-Saharan Africa: a review.

OBJECTIVE: To examine and establish complementary factors that contribute to the alarmingly high prevalence of HIV-1 in sub-Saharan Africa (SSA) in order to create awareness and suggest possible measures to avert the spread of the pandemic. DATA SOURCES: Review of literature via Medline, the Internet, articles in refereed journals, and un-refereed features from the East Africa media houses and personal communications. DATA SELECTION: Most published data from 1981 to September 2004 found to have revealed an impact on the spread of HIV-1 in SSA were included in the review. Therefore, all selected articles were read and critically evaluated. Where possible the number of citations articles which had been received were sought to established the degree of impact. DATA EXTRACTION: Abstracts of all articles identified were accessed, read and analysed to determined possible relevance to the spread of HIV-1. When relevance was established from the abstract the entire paper was read and important points were included in the review. DATA SYNTHESIS: A matrix was drawn to include all subtitles (e.g. polygamy, circumcision, poverty, etc). Below each subtitle all published works were included and prioritised. Published works that were found to have impact were included in the review. Finally a percent composite picture of all factors was drawn in an attempt to prioritise the factors, not withstanding the fact that most factors are interrelated and complementary. CONCLUSIONS: There are many reasons why the spread of HIV-1 in SSA has not been declining over the years. Main risk factors for HIV-1 infection and AIDS disease in SSA were found to include poverty, famine, low status of women in society, corruption, naive risk taking perception, resistance to sexual behaviour change, high prevalence of sexually transmitted infections (STI), internal conflicts and refugee status, antiquated beliefs, lack of recreational facilities, ignorance of individual's HIV status, child and adult prostitution, uncertainty of safety of blood intended for transfusion, widow inheritance, circumcision, illiteracy and female genital cutting and polygamy. It is suggested that control programmes both local and donor-driven seeking to mitigate the spread of HIV-1 in SSA should take into account the apparent multiplicity of sub-Saharan African cultures and beliefs, some of which augment the spread of HIV-1.

Plasma bioactive LH and testosterone profiles in male New Zealand rabbits experimentally infected with Schistosoma mansoni.

The effects of Schistosoma mansoni (S. mansoni) infection on plasma levels of bioactive luteinising hormone (LH) and testosterone in the New Zealand rabbit model were studied. S. mansoni infection significantly decreased the pulse frequency (P < 0.05), amplitude (P < 0.05), area under LH curve (P < 0.05) and mean plasma LH concentrations (P < 0.05) on days 42 and 70 post-infection, as compared to values for day 14 pre-infection. Areas under the response curves for plasma testosterone levels decreased significantly (P < 0.05) on days 42 and 70 post-infection in infected animals compared to day 14 pre-infection. In the praziquantel-treated group, the levels of LH and testosterone remained unchanged throughout the experimental period. The pulsatile secretion of LH was completely inhibited in S. mansoni-infected animals 70 days post-infection. These results suggest that the effects on reproductive gonadal hormones caused by S. mansoni in the rabbit model may partly be induced by alteration in pituitary synthesis or release of LH.

Hepatic granulomatous response to Schistosoma mansoni eggs in BALB/c mice and olive baboons (Papio cynocephalus anubis).

Hepatic granulomatous inflammation is one of the key pathological lesions of a patent Schistosoma mansoni infection. This study was concerned with the sequential induction, formation and eventual modulation of the schistosome egg granuloma in the mouse, which develops schistosome-induced hepatic fibrosis, and the olive baboon, which usually does not. Six baboons were each infected with 1500 S. mansoni cercariae and liver biopsies were collected at weeks 6, 9, 13 and 17 post-infection (p.i.). The mice (n=25) were each infected with 100 cercariae and killed in groups of five at weeks 6, 9, 12, 18 and 21 p.i. Peak granuloma size was observed at week 6 p.i. in baboons (mean 355 +/- 65.6 microm) but at week 12 p.i. in mice (299 +/- 40.5 microm). Eosinophils were more abundant in the baboon (60.6 +/- 8.9%) than in the mouse (41.2 +/- 8.4%) at the time of maximal granuloma size (P < 0.01). Neutrophils formed 21.1 +/- 6.3% of peak mouse granulomata but were virtually absent in baboon granulomata. A feature of the modulating baboon granulomata was the emergence of multinucleated giant cells (MGCs); modulating mouse granulomata, on the other hand, were characterized by infiltration of fibroblasts and collagen deposition. Thus, by week 21 p.i. mouse granulomata were 92 +/- 16.0 microm in diameter and well delineated by concentric layers of fibrous tissue. Granulomata, however, were present in only two of the baboons at week 17 p.i. (44 +/- 61.2 microm in diameter). The other four had peri-portal cellular infiltration without granuloma formation, implying that baboon granulomata resolve spontaneously. These data suggest that high tissue eosinophilia and MGC formation are particularly efficient in bringing about the destruction of schistosome eggs and subsequent resolution of the egg granuloma without fibrosis. In conclusion, the baboon model more closely mimics the pathogenesis observed in man than does the mouse model.

Repeated exposure induces periportal fibrosis in Schistosoma mansoni-infected baboons: role of TGF-beta and IL-4.

Recently, we observed that repeated Schistosoma mansoni infection and treatment boost Th2-associated cytokines and TGF-beta production in baboons. Other studies have shown that some chronically infected baboons develop hepatic fibrosis. Because TGF-beta, IL-2, and IL-4 have been shown to participate in development of fibrosis in murine schistosomiasis, the present study examined whether repeated exposure stimulates hepatic fibrosis in olive baboons. To test this hypothesis, animals were exposed to similar numbers of S. mansoni cercariae given once or repeatedly. After 19 wk of infection, animals were cured with praziquantel and reinfected once or multiple times. Hepatic granulomatous inflammation and fibrosis were assessed from serial liver biopsies taken at weeks 6, 9, and 16 after reinfection and egg Ag (schistosome egg Ag)-specific cytokine production by PBMC were measured simultaneously. Periportal fibroblast infiltration and extracellular matrix deposition (fibrosis), angiogenesis, and biliary duct hyperplasia developed in some animals. The presence and amount of fibrosis directly correlated with the frequency of exposure. Fibrosis was not associated with adult worm or tissue egg burden. The amount of fibrosis correlated with increased schistosome egg Ag-driven TGF-beta at 6, 9, and 16 wk postinfection (rs = 0.9, 0.8, and 0.54, respectively, all p < 0.01) and IL-4 production (p = 0.02) at 16 wk postinfection and not IFN-gamma, IL-2, IL-5, or IL-10. These data suggest that repeated exposure is a risk factor for periportal fibrosis by a mechanism that primes lymphocytes to produce increased levels of profibrotic molecules that include TGF-beta and IL-4.

Cytokine control of the granulomatous response in Schistosoma mansoni-infected baboons: role of exposure and treatment.

Variations in exposure and treatment may contribute to heterogeneity in immunity and granuloma-induced pathology in human schistosomiasis. To examine this hypothesis, olive baboons were either repeatedly infected with Schistosoma mansoni cercariae or received an equivalent dose in a single infection. They were then cured with praziquantel and reinfected with a single exposure. Serial liver biopsies were obtained throughout the course of the experiment, and cytokine responses by peripheral blood mononuclear cells were measured every 2 to 3 weeks. Reinfection after treatment resulted in a twofold-smaller granuloma size at 6 and 9 weeks after infection compared to the size for the same period after primary infection (P < 0.001) but had no effect at 16 or 19 weeks postinfection. The pattern of exposure did not influence granuloma size. During primary infection schistosome-soluble egg antigen (SEA)-induced cytokine production correlated with granulomatous inflammation. Cytokine levels peaked during the acute infection, declined with chronic infection, and became undetectable after treatment. Reinfection after treatment stimulated a two- to three-fold increase in SEA-specific interleukin-4 (IL-4), IL-5, IL-10, IL-2, and transforming growth factor beta (TGF-beta) production and a marked rise in SEA-specific immunoglobulin E (IgE) and IgG regardless of the type of exposure. Cytokine production was significantly greater in repeatedly exposed animals (P < 0.001). SEA-induced gamma interferon production, however, did not increase with reinfection after treatment. SEA-induced TGF-beta was the only cytokine that remained elevated as the infection become chronic and correlated with diminished hepatic granuloma size, implying its participation in down-modulation. These studies demonstrate that baboons partially retain their ability to down-modulate the granulomatous response after treatment.

The baboon as a non-human primate model of human schistosome infection.

Over the past three decades, intensive studies of murine schistosomiasis have provided important clues to the understanding of the human disease, but growing evidence suggests that these results derived from highly inbred strains of mice might not have direct applicability to the human infection. Recent data based on the baboon indicate that infection in this non-human primate might mirror the human situation. In this review, Mramba Nyindo and Idle Farah demonstrate that baboons provide an excellent non-human primate model that produces pathology and disease closely resembling that observed in humans, and address how studies in baboons can provide insights into mechanisms regulating schistosomiasis mansoni pathology and immunity. They also address, in a general way, issues related to the use of non-human primates in biomedical research.

Role of adult worm antigen-specific immunoglobulin E in acquired immunity to Schistosoma mansoni infection in baboons.

Allergic-type immune responses, particularly immunoglobulin E (IgE), correlate with protective immunity in human schistosomiasis. To better understand the mechanisms of parasite elimination we examined the immune correlates of protection in baboons (Papio cynocephalus anubis), which are natural hosts for Schistosoma mansoni and also develop allergic-type immunity with infection. In one experiment, animals were exposed to a single infection (1,000 cercariae) or were exposed multiple times (100 cercariae per week for 10 weeks) and subsequently were cured with praziquantel prior to challenge with 1, 000 cercariae. Singly and multiply infected animals mounted 59 and 80% reductions in worm burden, respectively (P < 0.01). In a second experiment, animals were inoculated with S. mansoni ova and recombinant human interleukin 12 (IL-12). This produced a 37 to 39% reduction in adult worm burden after challenge (P < 0.05). Parasite-specific IgG, IgE, IgM, and peripheral blood cytokine production were evaluated. The only immune correlate of protection in both experiments was levels of soluble adult worm antigen (SWAP)-specific IgE in serum at the time of challenge infection and/or 6 weeks later. Baboons repeatedly infected with cercariae or immunized with ova and IL-12 developed two- to sixfold-greater levels of SWAP-specific IgE in serum than did controls, and this correlated with reductions in worm burden (r2, -0.40 to -0.64; P, <0. 01). Thus, in baboons and unlike mice, adult worm-specific IgE is uniquely associated with acquired immunity to S. mansoni infection. This similar association of parasite-specific IgE and protection among primates infected with schistosomiasis, along with similar pathology, anatomy, and genetic make-up, indicates that baboons provide an excellent permissive experimental model for better understanding the mechanisms of innate and acquired immunity to schistosomiasis in humans.

Peri-portal fibrosis of the liver due to natural or experimental infection with Schistosoma mansoni occurs in the Kenyan baboon.

The chronic granulomatous inflammation that occurs during schistosomiasis mansoni and its reparative healing lead to hepatic fibrosis, with subsequent portal hypertension (a life-threatening sequela). In the murine model, granuloma modulation invariably leads to formation of fibrous tissue and disposition of extracellular matrix. Typically, < 10% of patients infected with Schistosoma mansoni progress to clay-pipe-stem fibrosis. Similar fibrosis occurs in chimpanzees during experimental infections. Although previous studies of schistosomiasis mansoni in Kenyan baboons have failed to demonstrate appreciable liver fibrosis, classical peri-portal fibrosis has now been observed in the livers of three yellow baboons (Papio cynocephalus cynocephalus) with natural S. mansoni infections and three olive baboons (P. c. anubis) with experimental infections after each was challenged with 1000 S mansoni cercariae. The peri-portal fibrosis was indicated by marked fibroblast accumulation, increased collagen deposition, bile-duct hyperplasia and blood-vessel proliferation. The lesions were more severe in the naturally infected baboons than in those experimentally infected. No accompanying portal hypertension, ascites or portocaval anastomosis was noted in any of the animals. The development of the baboon as a model for chronic human schistosomiasis mansoni may be feasible.

Schistosoma mansoni: development and modulation of the granuloma after or multiple exposures in the baboon (Papio cynocephalus anubis).

The ability of the host to modulate the granulomatous response around ova trapped in tissues determines the severity of disease to schistosome infections. Multiple factors may affect this modulation such as age, prior sensitization, history of treatment, and exposure. The present study examines the effect of different patterns of exposure on the sequential development and modulation of granuloma in juvenile Kenyan baboons (Papio cynocephalus anubis) after receiving either a single infection (SI) of 1500 Schistosoma mansoni cercariae or multiple infections (MI) of 150 cercariae, once a week for 10 weeks. Prior to sacrifice at 17 weeks postinfection (p.i.), liver biopsies were obtained at Weeks 0, 6, 9, and 13. SI animals experienced more prolonged dysentery and greater weight loss compared to MI animals. Peak hepatic granuloma size (mean 355 +/- 65.5 microns diameter), the maximum percentage of eosinophils in the granuloma (61%), and severity of disease occurred at 6 weeks in SI animals. Peak granuloma size and pathology did not appear until Week 9 in the MI animals (mean 317.7 +/- 67.3 microns diameter). Granuloma size, tissue eosinophilia, and gross pathology diminished by Week 13 p.i. and were virtually absent in both groups by Week 17. The decrease in granuloma size, pathology, and clinical illness resolved more rapidly in the MI baboons. Singly infected baboons were more susceptible to infection (83 +/- 12% of cercariae developed into adult worms) compared to MI baboons (67 +/- 7%, P < 0.01). Eggs recovered from tissues at necropsy were primarily confined to the large intestine (85% of total egg recovered), followed by liver (10%) and small intestine (5%). Significantly more eggs were recovered from MI compared to SI animals, indicating a higher fecundity of female worms in the MI baboons. These date demonstrate that granulomatous responses develop more slowly and modulate more rapidly with repeated infection compared to a single heavy infection and suggest the type of exposure may affect the pathologic response to infection.

Acute schistosomiasis mansoni in the baboon Papio anubis gives rise to goblet-cell hyperplasia and villus atrophy that are modulated by an irradiated cercarial vaccine.

A histopathology study of the intestines of four Kenyan baboons (Papio anubis) infected by 800 cercariae of Schistosoma mansoni and euthanized at 10 weeks postinfection was done. The pathology was compared with that of four baboons first vaccinated with 10,000 irradiated cercariae and then challenged 8-10 weeks later with the same number of cercariae. Two baboons that were neither vaccinated nor challenged were used as controls. On postmortem examination, multifocal to coalescing granulomatous inflammatory responses to the eggs in the submucosa of the terminal ileum and colon were seen in all baboons exposed to the parasite. The mean numbers of goblet cells detected per villus at 20 cm from the pylorus were 12.8 +/- 2.6, 30.4 +/- 6.6, and 20.2 +/- 3.7 in the two uninfected baboons, the infected unvaccinated baboons, and the vaccinated and challenged baboons, respectively. Mild to total villus atrophy was present in all eight baboons exposed to the parasite. These lesions, which were less marked in infected but vaccinated baboons, may contribute to the clinical signs seen in acute simian schistosomiasis mansoni.

Schistosoma mansoni induces in the Kenyan baboon a novel intestinal pathology that is manifestly modulated by an irradiated cercarial vaccine.

Light and scanning electron microscopic study of intestines of 5 baboons (Papio anubis) in a state of acute schistosomiasis mansoni after exposure to 800 cercariae was made. In addition to overt granulomatous inflammation in the mucosa of the colon and ileum, more subtle microscopic lesions consisting of smooth muscle hypertrophy and villous atrophy were present. The intensity and distribution of these lesions were less marked in 5 baboons previously vaccinated with 40,000 30-krad-attenuated cercariae and presenting a 39% mean protection level measured as a percent reduction in adult worms recovered from mesenteric vasculature at perfusion. No similar lesions were observed in 2 normal uninfected and nonvaccinated baboons. These results are comparable to what has been reported in mice infected by Schistosoma mansoni. The data indicate that villous atrophy, hypertrophy of muscularis mucosa, nd goblet cell hyperplasia are important pathological changes to be included in the evaluation of the efficacy of schistosomiasis vaccines in the baboon model, together with the routine adult worm recovery from mesenteric blood vessels and the overt liver and bowel pathology.

Immunity induced by vaccination with Rhipicephalus appendiculatus salivary gland antigens does not augment protective immunity acquired naturally by exposing rabbits to adult ticks.

A study was conducted using rabbits to ascertain the effects of immunity induced with salivary gland antigens (SGA) on naturally acquired host resistance, which was confirmed by exposing groups of rabbits to adult Rhipicephalus appendiculatus (Neumann) ticks. A reciprocal experiment was conducted to establish the effect of naturally acquired resistance on vaccination with SGA. After the acquisition of resistance by either method of vaccination, rabbits were then challenged with the 3 life stages of the tick. Results of the experiment demonstrated 3 phenomena: infestation of rabbits with 60 adult ticks leads to high protection in terms of reduction in the engorged weight against adult ticks, larvae, and nymphs (88.6, 31.5, and 55.9%, respectively); vaccination alone provides 53.9, 29.7, and 35.7% reduction in adult, larval, and nymphal ticks, respectively; and vaccination of rabbits already exposed to adult tick infestation appeared to have no additive immunological benefit above that already provided by adult ticks. Sodium dodecyl polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting analyses revealed that antibodies with high avidity to SGA were directed to a 39-kDa polypeptide. This polypeptide was not revealed by sera from rabbits that were first infested with adult ticks. Sera from rabbits that were first vaccinated with SGA consistently reacted with the 39-kDa polypeptide. Sera from rabbits that were infested recognized strongly a 42-kDa polypeptide among 5 polypeptides in the SGA. Results of the experiment show that resistance resulting from adult tick infestation is not augmented by immunity caused by vaccination with SGA.

Schistosoma mansoni in the baboon: modulation of pathology after vaccination with polyclonal anti-idiotypic antibodies.

Vaccination of five baboons with an anti-idiotypic vaccine to irradiated Schistosoma mansoni cercariae resulted in nearly 19% protection compared to 39% protection conferred to five baboons vaccinated with an irradiated vaccine. Vaccination with the anti-idiotypic antibodies resulted in a significant reduction of pathology and granuloma size following challenge with live unattenuated cercariae. Results presented in this work are considered highly significant because the anti-idiotypic vaccine markedly influenced schistosomiasis morbidity which is the main consideration in this disease.

Protective immunity in baboons vaccinated with a recombinant antigen or radiation-attenuated cercariae of Schistosoma mansoni is antibody-dependent.

Mice vaccinated with radiation-attenuated cercariae of Schistosoma mansoni exhibit high levels of resistance to challenge infection. We have previously shown that sera from these mice recognize polypeptides that are expressed on the surface of newly transformed schistosomula. We have cloned and sequenced a cDNA that encodes a 62-kDa portion of one of these polypeptides. Vaccination of mice with this 62-kDa polypeptide (designated rlrV-5) elicits high antibody titers and significant resistance to challenge infection. We report here the results of a vaccination trial in baboons with the rlrV-5 or radiation-attenuated cercariae. rlrV-5 was presented either in the form of protein micelles or complexed with the outer membrane protein of meningococcus to form proteosomes. The level of protection achieved in these groups ranged from 0 to 54%, with a mean of 27.7%. In baboons exposed to radiation-attenuated cercariae the level of protection was very high, with a mean of 84%. The resistance observed after vaccination with rlrV-5 or radiation-attenuated cercariae was reflected in the overall histopathology. Vaccination of baboons with rlrV-5 or radiation-attenuated cercariae elicited an antibody response against epitopes exposed on the surface of newly transformed schistosomula. In the case of baboons vaccinated with radiation-attenuated cercariae, this response was not limited to epitopes encompassed by rlrV-5. Analysis of individual baboon sera by ELISA demonstrated that there was a direct correlation between the anti-rlrV-5 titer and resistance to challenge worm burden, suggesting that the immunoprotective mechanism is antibody-dependent.

Augmentation of host's naturally acquired immunity by solubilized membrane-bound midgut proteins of the tick Rhipicephalus appendiculatus.

Immune resistance of rabbits to the hard tick Rhipicephalus appendiculatus induced by combined tick infestations and immunization with solubilized midgut membrane proteins were compared with resistance due to 1-3 infestations or immunization alone. Results demonstrate that the level of exposure of rabbits to ticks used in the study does not significantly affect the immune expression resulting from immunization and that the latter augments the resistance due to infestation.

Antigenic analysis of four species of the genus Ehrlichia by use of protein immunoblot.

The antigenic profile of Ehrlichia canis, E risticii, E sennetsu, and E equi was investigated by the use of protein (western) immunoblot technique. Results of analysis of serum from acutely and chronically infected animals indicated that the 4 Ehrlichia species share a unique 25-kD polypeptide in addition to other peptides. Immune sera from dogs inoculated with E canis recognized a wide range of E canis polypeptide antigens, as determined by western blot analysis. A larger number of E sennetsu polypeptides were detected when homologous antiserum and antiserum to E equi were used. The latter antiserum did not recognize antigens of E canis or E risticii. Antisera to E canis, E risticii, and E sennetsu detected E equi antigens. Data indicate that a 25-kD protein is a common antigen among the species of the genus Ehrlichia and that the ascending order of abundance of immunodominant determinants in the 4 species of Ehrlichia studied would be: E risticii----E equi----E sennetsu----E canis. Implications of these findings for diagnosis of ehrlichial infections and prophylaxis are evident.

Ultrastructural changes in salivary glands of tsetse, Glossina morsitans morsitans, infected with virus and rickettsia-like organisms.

Electron microscope observations on enlarged hypertrophied salivary glands dissected from adult laboratory-reared male Glossina morsitans morsitans show a concurrent infection of the salivary gland tissue with rod-shaped virus particles and intracellular rickettsia-like organisms. The latter are found intracellular in the epithelium and in the gland lumen enclosed within lytic zones. The virus particles are found within the degenerating cytoplasm, nuclei, and lumen of the cell where they are especially numerous. Stratified epithelium and gland enlargement are a prominent feature of the infection. These observations suggest that biological associations between salivary gland tissue and diverse microbes may be more common than formerly recognized. The microbes appear to cause damage to salivary gland cells, causing hyperplasia which assumes pathologic proportions.

The interaction between the immune response of rabbits to heterologous antigens and a primary infestation with Rhipicephalus evertsi evertsi.

Rhipicephalus evertsi evertsi feeding on hosts inoculated with sheep red blood cells (SRBC) and bovine serum albumin (BSA) suppressed the primary antibody response to the two antigens. In addition, while the ticks paralysed most hosts in the studies, fatality associated with this toxicosis occurred only in rabbits which had received SRBC, either alone or with BSA. Only those hosts inoculated with BSA developed any resistance against the ticks, manifested by a slight reduction of engorged weights and development of anti-tick antibodies. These results suggest that R. e. evertsi infestation induces a degree of reduced host immune responsiveness to heterologous antigens.

Immunization against ticks: use of salivary gland antigens and infestations with Rhipicephalus appendiculatus (Acari: Ixodidae) in rabbits.

Comparative immunogenicity of salivary gland antigens (SGA) derived from adult Rhipicephalus appendiculatus (Neumann) and experimental infestations with the three stages of the tick was investigated. The best immunization schedule judged by reduction of engorgement weights and hatchability resulted from nymphal and adult tick infestations. Inoculation of rabbits with SGA in Freund's incomplete adjuvant (FIA) induced immune responses comparable to those associated with larval infestations, but less than those produced by nymphal or adult tick infestations. High antibody titers directed against SGA were detected only in the vaccinated and adult tick-infested rabbits. The results of this experiment suggest that SGA prepared from partially fed ticks can be used in the experimental induction of immunity to ticks and that the antigen has potential as a vaccine against R. appendiculatus ticks.

Acquired resistance in rabbits to immature stages of Rhipicephalus evertsi evertsi.

Host resistance, accompanied by demonstrable anti-tick antibodies, developed in groups of rabbits that were infested repeatedly with different numbers of Rhipicephalus evertsi evertsi larvae. This resistance was associated with a drastic reduction in the number of ticks that attached but not in the ability to feed and moult by immatures already established on the hosts. Furthermore, resistance reduced to below 50% the proportion of nymphs which emerged from the larvae applied to the three host groups. Nymphs weighing 5-9.9 and 15-19.9 mg moulted to give mainly males or females respectively. The proportion of males and females which moulted from the remaining weight categories was variable. Anti-tick antibodies were detected by enzyme-linked immunosorbent assay as early as 7 days after primary infestation in all hosts. The titres plateaued after the second challenge and declined drastically during the fifth infestation. No appreciable differences were observed in the antibody responses stimulated by different challenge regimens.