Molecular crosstalks in Leishmania-sandfly-host relationships

Sandflies (Diptera: Phlebotominael are vectors of Leishmania parasites, causative agents of important human and animal diseases with diverse manifestations. This review summarizes present knowledge about the vectorial part of Leishmania life cycle and parasite transmission to the vertebrate host. Particularly, it focuses on molecules that determine the establishment of parasite infection in sandfly midgut. It describes the concept of specific versus permissive sandfly vectors, explains the epidemiological consequences of broad susceptibility of permissive sandflies and demonstrates that genetic exchange may positively affect Leishmania fitness in the vector. Last but not least, the review describes recent knowledge about circulating antibodies produced by hosts in response to sandfly bites. Studies on specificity and kinetics of antibody response revealed that anti-saliva IgG could be used as a marker of host exposure to sandflies, i.e. as a useful tool for evaluation of vector control.     

Sandfly midgut lectin: effect of galactosamine on Leishmania major infections

Galactosamine, which has been shown in vitro to specifically inhibit sandfly midgut lectin activity, was fed to Phlebotomus duboscqi females with blood containing promastigotes of Leishmania major . Non-inhibitory sugar, galactose, was added in controls. For two strains of L. major (LV 561 and Neal-P), galactosamine substantially enhanced the establishment of infection in the sandfly posterior midgut and significantly increased parasite loads after defaecation, but did not affect anterior migration of Leishmania . On day 3 post-infection, most infections in galactosamine-fed sandfly groups (92% of LV 561 and 100% of Neal-P) were found in the ectoperitrophic space of the posterior midgut, whereas most infections in the galactose-fed groups of sandflies (85% in LV 561 and 96% in Neal-P) were restricted to the peritrophic sac. On day 9, however, the proportion of infections colonizing the stomodeal valve was similar in both dietary groups of sandflies for both strains of L. major . The addition of galactosamine prevented the decrease of parasite loads which occurred in controls between days 3 and 6 post-infection. On days 6 and 9, heavy infections were observed almost exclusively in galactosamine-fed females. Differences between groups were more pronounced for the Neal-P strain, which normally developed poorly in sandflies. Morphology of L. major LV 561 was not affected by galactosamine supplement: the lengths of parasite body and flagellum were similar in both sandfly groups. Two hypotheses are considered for the role of sandfly midgut lectin in Leishmania development in the vector midgut. One proposes that sandfly lectin kills Leishmania promastigotes, the other assumes that lectin blocks LPG-mediated binding of promastigotes to sandfly midgut microvilli.     

Leishmania infection in humans, dogs and sandflies in a visceral leishmaniasis endemic area in Maranhão, Brazil

Leishmania infection in humans, dogs and sandflies was examined in the endemic visceral leishmaniasis (VL) municipality of Raposa, state of Maranh?o, Brazil. In this study, we examined Leishmania chagasi infection in the blood serum of both humans and Canis familiaris and the natural Leishmania sp. infection rate in the sandfly vector, Lutzomyia longipalpis. Enzyme-linked immunosorbent assay, indirect immunofluorescence reaction and polymerase chain reaction were performed to detect Leishmania infections in humans, dogs and sandflies, respectively. Overall, 186 out of 986 studied human beings were infected with L. chagasi parasites, representing an infection prevalence of 18.9%. An even higher infection rate was detected in dogs, where 66 (47.8%) out of 138 were infected. Among all Lu. longipalpis captured (n = 1,881), only 26.7% were females. The Leishmania infection frequency for the vector Lu. longipalpis was 1.56%. Remarkably, all infected sandflies were found in the peridomiciliary area. Furthermore, a high incidence of asymptomatic forms of VL in the human and canine populations was observed. The results of this study suggest autochthonous transmission of L. chagasi in this endemic area for visceral leishmaniasis because infection by Leishmania sp. was identified in all important elements of the transmission chain.     

Xenodiagnosis using Lutzomyia youngi in Venezuelan cases of cutaneous leishmaniasis due to Leishmania braziliensis

Eight patients infected with Leishmania braziliensis were used for xenodiagnosis with Lutzomyia youngi, before and after specific antileishmanial treatment with "glucantime" and "gabbromycin". All of them infected sandflies fed on the borders of the skin lesions before the treatment, suggesting that infected persons might act as reservoirs of infection for an indoor-biting sandfly species. The negative results obtained by xenodiagnosis carried out after specific treatment of the same individuals indicated cure of the patients, and a reduction of risk for further intradomiciliary transmission.     

DNA hybridizations on squash-blotted sandflies to identify both Phlebotomus papatasi and infecting Leishmania major

Epidemiological field studies on leishmaniasis have been hampered by the laborious, and often inefficient, methods used to assess the rates of infection of sandfly vectors (Diptera; Phlebotominae) by species of the causative disease organisms, protozoal parasites of the genus Leishmania (Kinetoplastida; Trypanosomatidae). We report the rapid and accurate identification of both sandfly vector (Phlebotomus (Phlebotomus) papatasi (Scopoli] and infecting Leishmania major Yakimov & Schokov by DNA hybridizations to squash-blotted sandflies. Large numbers of whole (infected) sandflies can be quickly squashed on to nylon hybridization filters and (following standard procedures) the filter-bound DNA can be hybridized sequentially to cloned, multicopy genomic sequences that are specific for species of Leishmania (kinetoplast DNA) or for the sandfly (ribosomal (r) DNA). Our sandfly probe consists of a 3.2 kb fragment of the intergenic 'non-transcribed' spacer of rDNA of P. papatasi that we have detected only in this species: it is present in all six geographically isolated populations tested (from Tunisia through to India) but cannot be detected in the morphologically similar P. (Phlebotomus) duboscqi Neveu-Lemaire, the vector of Leishmania major south of the Sahara; it also cannot be detected in Phlebotomus species of the subgenera Larroussius and Paraphlebotomus that together with P. papatasi are the dominant man-biting sandflies in north African foci of zoonotic cutaneous leishmaniasis, where (as in many arid regions of western Asia) P. papatasi is believed to be the sole vector of L. major.     

Filamentous proteophosphoglycan secreted by Leishmania promastigotes forms gel-like three-dimensional networks that obstruct the digestive tract of infected sandfly vectors

Development of Leishmania parasites in the digestive tract of their sandfly vectors involves several morphological transformations from the intracellular mammalian amastigote via a succession of free and gut wall-attached promastigote stages to the infective metacyclic promastigotes. At the foregut midgut transition of Leishmania-infected sandflies a gel-like plug of unknown origin and composition is formed, which contains high numbers of parasites, that occludes the gut lumen and which may be responsible for the often observed inability of infected sandflies to draw blood. This "blocked fly" phenotype has been linked to efficient transmission of infectious metacyclic promastigotes from the vector to the mammalian host. We show by immunofluorescence and immunoelectron microscopy on two Leishmania/sandfly vector combinations (Leishmania mexicana/Lutzomyia longipalpis and L. major/Phlebotomus papatasi) that the gel-like mass is formed mainly by a parasite-derived mucin-like filamentous proteophosphoglycan (fPPG) whereas the Leishmania polymeric secreted acid phosphatase (SAP) is not a major component of this plug. fPPG forms a dense three-dimensional network of filaments which engulf the promastigote cell bodies in a gel-like mass. We propose that the continuous secretion of fPPG by promastigotes in the sandfly gut, that causes plug formation, is an important factor for the efficient transmission to the mammalian host.     

Leishmania (Leishmania) major-infected rhesus macaques (Macaca mulatta) develop varying levels of resistance against homologous re-infections

Seven rhesus macaques were infected intradermally with 10(7) promastigotes of Leishmania (Leishmania) major. All monkeys developed a localized, ulcerative, self-healing nodular skin lesion at the site of inoculation of the parasite. Non-specific chronic inflammation and/or tuberculoid-type granulomatous reaction were the main histopathological manifestations of the disease. Serum Leishmania-specific antibodies (IgG and IgG1) were detected by ELISA in all infected animals; immunoblot analyses indicated that numerous antigens were recognized. A very high degree of variability was observed in the parasite-specific cell-mediated immune responses [as detected by measuring delayed-type hypersensitivity (DTH) reaction, in vitro lymphocyte proliferation, and gamma interferon (IFN-gamma) production] for individuals over time post challenge. From all the recovered monkeys (which showed resolution of the lesions after 11 weeks of infection), 57.2% (4/7) and 28.6% (2/7) animals remained susceptible to secondary and tertiary infections, respectively, but the disease severity was altered (i.e. lesion size was smaller and healed faster than in the primary infection). The remaining monkeys exhibited complete resistance (i.e. no lesion) to each rechallenge. Despite the inability to consistently detect correlates of cell-mediated immunity to Leishmania or correlation between resistance to challenge and DTH, lymphocyte transformation or IFN-gamma production, partial or complete acquired resistance was conferred by experimental infection. This primate model should be useful for measuring vaccine effectiveness against the human disease.     

Leishmania-sandfly interactions: an empirical field study

Phlebotomus papatasi is the sandfly vector of Leishmania major in the Jordan Valley. The objective of this study was to characterize vector-parasite relations in an active zoonotic focus. Seasonality and intensity of promastigote infection rates in female sandflies and the developmental stage of these hosts were established. On 153 trap-nights, 641 female P. papatasi were caught and examined. Of these, 48 (7.4%, range 12.9-4.8%) were infected with L. major promastigotes. Correlating the number of parasites with the gonotrophic age of the vector revealed that most infections initially are light ones, and those that survive in the vector generally prosper and proliferate. Comparing infection rates in parous and gravid flies revealed that similar proportions of gravid and parous flies are found infected. Thus, Leishmania infections do not appear to affect sandfly survival.     

Leishmania infantum infection rates in Phlebotomus perniciosus fed on naturally infected dogs under antimonial treatment

Dogs naturally infected with Leishmania infantum Nicolle were treated with three courses of meglumine antimoniate. Changes were observed in the dogs' clinical signs, antibody titres and in infection rates of Phlebotomus perniciosus Newstead fed on the dogs. A large reduction in the sandfly infection rate was observed for 4-5 months after the first treatment. The use of antimonial drugs is advocated for the control of canine leishmaniasis and to reduce risks of L.infantum transmission.     

Prevention and control of leishmaniasis vectors: current approaches

Phlebotomine sandflies (Diptera: Psychodidae) are the suspected or proven vectors of Leishmania spp. in at least 88 countries, including over 40 Phlebotomus species in the Old World and a further 30 belonging to the genus Lutzomyia in the New World. In recent years, both cutaneous (CL) and zoonotic visceral leishmaniasis (ZVL) have become increasingly prevalent in urban areas, including large Latin American cities. A similar trend has been recorded in all Mediterranean areas during the last decade. Based on mathematical models, insecticidal control of sandflies appears to represent a more effective way of reducing Leishmania infantum transmission than the present strategy of culling infected dogs in Latin America as well as being more acceptable to the human population. Since man is a dead-end host of most Leishmania species, treatment of existing human cases generally does not affect transmission. Interruption of the cycle by vector control may offer a cheaper, more practical solution to treatment and improved knowledge of the alternatives available could lead to preventative measures being undertaken in more leishmaniasis foci. In this note a review of current knowledge on sandfly control is presented. Different measures to control phlebotomine sandflies, including residual spraying of dwellings and animal shelters, insecticide treated nets, application of repellents/insecticides to skin or to fabrics and impregnated dog collars are discussed. Although effective in urban areas with high concentrations of sandflies, residual spraying of insecticides is no often longer tenable in most situations. In rural areas where dwellings are more dispersed and surrounded by large, untargeted "reservoir" populations of sandflies, residual spraying of houses may be both impractical for logistic reasons and ineffective. Actually, this control measure depends on the availability of a suitable public health infrastructure, including adequate supplies of insecticide, spraying equipment and trained personnel. Ideally such personnel should be trained in insecticide application, monitoring techniques and interpretation of sampling data, as well as safety techniques. To date reports of resistance refer to one insecticide (DDT) in only three species (Phlebotomus papatasi, P. argentipes and Sergentomyia shorti) in one country (India), although there are reports of increased tolerance to this compound in several countries. Fortunately the insects remain susceptible to all the major insecticidal groups. Impregnated bednets may offer the best solution in rural areas where transmission is largely intradomiciliary. This measure has the advantage that it can be employed at the individual household level and affords collateral benefits such as privacy and control of other biting insects such as mosquitoes, fleas and bedbugs. Sandfly larvae are generally difficult to find in nature so control measures that act specifically against immatures are not feasible, although the effectiveness of a few biological and chemical agents has been demonstrated in laboratory evaluations. In ZVL foci, where dogs are the unique domestic reservoir, a reduction in Leishmania transmission would be expected if we could combine an effective mass treatment of infected dogs with a protection of both healthy and infected dogs from the sandfly bites. Laboratory and field evaluations have shown that impregnated dog collars and topical application of insecticides could protect dogs from most sandfly bites by means of both anti-feeding and killing effect of the pirethorids used.     

Bloodmeal digestion and Leishmania major infections in Phlebotomus duboscqi: effect of carbohydrates inhibiting midgut lectin activity

The carbohydrates galactosamine and heparin, previously shown to inhibit phlebotomine lectin activity in vitro, were fed to the sandfly Phlebotomus duboscqi Neveu-Lemaire (Diptera: Psychodidae) with blood, and the effects on mortality, fecundity, protease activity and susceptibility to Leishmania major Yakimoff & Schokhor (Kinetoplastida: Trypanosomatidae) were studied. Previous study revealed that galactosamine considerably enhanced the establishment of L. major infection in P. duboscqi and significantly increased parasite loads in late infections. This work demonstrates a similar but less pronounced effect of heparin. Heparin increased infection rates and parasite loads 3 and 9 days post-feeding but did not affect the location of Leishmania promastigotes and their anterior migration. Galactosamine supplement caused pronounced changes in bloodmeal digestion. It abolished the activity of alkaline proteases and trypsin, caused premature defecation of bloodmeal, increased mortality of female sandflies in days 1-4 post-feeding and decreased their fecundity. Heparin had a less pronounced effect on sandfly physiology. It lowered trypsin activity 12 and 72 h post-bloodmeal but did not alter defecation, mortality and oviposition. The data suggest that the enhancing effect of these carbohydrates on Leishmania infections in sandfly midgut could be explained by their interference with midgut proteases. The study supports the hypothesis that proteolytic activities of midgut proteases strongly influence the vector competence of sandflies.     

Immunization with a live, attenuated simian immunodeficiency virus (SIV) prevents early disease but not infection in rhesus macaques challenged with pathogenic SIV.

An infectious, virulence-attenuated molecular clone of simian immunodeficiency virus (SIV), SIVMAC-1A11, was derived from an SIV isolate that causes fatal immunodeficiency in rhesus macaques. When inoculated intravenously in rhesus macaques, SIVMAC-1A11 induced transient viremia (1 to 6 weeks) without clinical disease and a persistent humoral antibody response. The antibodies were directed mainly against the viral envelope glycoproteins, as determined by immunoblots and virus neutralization. The potential of this virulence-attenuated virus to protect against intravenous challenge with a pathogenic SIVMAC strain was assessed. Five rhesus macaques were each given two intravenous inoculations with SIVMAC-1A11 7 months apart. Three of the five immunized monkeys and four naive control animals were then challenged with 100 to 1,000 100% animal infectious doses of pathogenic SIVMAC. All seven animals became persistently viremic following the challenge. Four of four unimmunized animals developed severe clinical signs of simian acquired immunodeficiency syndrome by 38 to 227 days after challenge and were euthanatized 91 to 260 days postchallenge. However, no signs of illness were seen in immunized monkeys until 267 to 304 days postchallenge, when two of three immunized animals developed mild thrombocytopenia and lymphopenia; one of these animals died with clinical signs of simian immunodeficiency disease at 445 days after challenge. The two SIVMAC-1A11-immunized monkeys that were not challenged were healthy and antibody positive 22 months after the initial immunization. Thus, although live SIVMAC-1A11 was immunogenic and did not induce any disease, it failed to protect rhesus macaques against infection with a moderately high dose of pathogenic virus. However, immunization prevented severe, early disease and prolonged the lives of monkeys subsequently infected with pathogenic SIV.     

Phlebotomine sandfly ecology on the Indian subcontinent: does village vegetation play a role in sandfly distribution in Bihar,India?

Visceral leishmaniasis (VL) is a disease that results in approximately 50 000 human deaths annually. It is transmitted through the bites of phlebotomine sandflies and around two‐thirds of cases occur on the Indian subcontinent. Indoor residual spraying (IRS), the efficacy of which depends upon sandfly adults resting indoors, is the only sandfly control method used in India. Recently, in Bihar, India, considerable sandfly numbers have been recorded outdoors in village vegetation, which suggests that IRS may control only a portion of the population. The purpose of this study was to revisit previously published results that suggested some sandflies to be arboreal and to rest on outlying plants by using Centers for Disease Control light traps to capture sandflies in vegetation, including banana plants and palmyra palm trees, in two previously sampled VL‐endemic Bihari villages. Over 3500 sandflies were trapped in vegetation over 12 weeks. The results showed the mean number of sandflies collected per trap night were significantly higher in banana trees than in other vegetation (P = 0.0141) and in female rather than male palmyra palm trees (P = 0.0002). The results raise questions regarding sandfly dispersal, oviposition and feeding behaviours, and suggest a need to refine current control practices in India and to take into account an evolving understanding of sandfly ecology.     

Study of the safety,immunogenicity and efficacy of attenuated and killed Leishmania (Leishmania) major vaccines in a rhesus monkey (Macaca mulatta) model of the human disease

We have compared the efficacy of two Leishmania (Leishmania) major vaccines, one genetically attenuated (DHFR-TS deficient organisms), the other inactivated [autoclaved promastigotes (ALM) with bacillus Calmete-Guérin (BCG)], in protecting rhesus macaques (Macaca mulatta) against infection with virulent L. (L.) major. Positive antigen-specific recall proliferative response was observed in vaccinees (79% in attenuated parasite-vaccinated monkeys, versus 75% in ALM-plus-BCG-vaccinated animals), although none of these animals exhibited either augmented in vitro gamma interferon (IFN-gamma) production or positive delayed-type hypersensitivity (DTH) response to the leishmanin skin test prior to the challenge. Following challenge, there were significant differences in blastogenic responses (p < 0.05) between attenuated-vaccinated monkeys and na?ve controls. In both vaccinated groups very low levels of antibody were found before challenge, which increased after infective challenge. Protective immunity did not follow vaccination, in that monkeys exhibited skin lesion at the site of challenge in all the groups. The most striking result was the lack of pathogenicity of the attenuated parasite, which persisted in infected animals for up to three months, but were incapable of causing disease under the conditions employed. We concluded that both vaccine protocols used in this study are safe in primates, but require further improvement for vaccine application.     

Protection of dogs from bites of phlebotomine sandflies by deltamethrin collars for control of canine leishmaniasis

Abstract. Dog collars made of PVC plastic impregnated with the pyrethroid insecticide deltamethrin at 40 mg/g were investigated for their protective efficacy against phlebotomine sandflies. Collared dogs were kept separately (two untreated control dogs lived together) in outdoor enclosures, each with a kennel, in the Cevennes, southern France. To measure sandfly mortality and anti-feeding effects due to the deltamethrin-impregnated collars worn continuously by the dogs for up to 8 months, each dog was periodically sedated and exposed for 2h to 150–200 laboratory-reared Phlebotomus perniciosus females (plus c. 25 males) inside a net (1.2m square, 1.8 m high) indoors. After dogs were removed from the nets, allowed to recover and returned to their kennels, any dead sandflies were collected from inside the net and counted. Surviving flies were kept overnight, then scored according to whether they were still alive or dead, unfed or blood-fed. From tests 2, 3, 4, 13, 20, 26 and 34 weeks after the dogs began wearing collars, the overall numbers of blood-fed female sandflies recaptured were 75 from two dogs with collars, compared with 1911 from two collarless dogs. Thus, for every 100 flies which fed on collarless dogs, only 4 fed on collared dogs, i.e. the collars protected dogs from 96% of the bites and this activity was maintained for up to 34 weeks. During the same period, the percentage of recaptured female sandflies that had fed on collared dogs was 0–12% compared to 55–95% on collarless dogs. Immediately after dogs were taken out of the nets, 21–60% of flies confined with the collared dogs were found dead, compared to 0–12% with the controls. It is concluded that, at least in the Mediterranean subregion, this insecticidal collar would protect a dog from the majority of sandfly bites and retain a killing effect for a complete sandfly season. Moreover, it seems likely that the use of collars on all dogs in a focus of Leishmania infantum would reduce contact between sandfly vectors and canine reservoir hosts sufficiently to diminish the risk of infection for humans as well as dogs.     

Immunological and pathological evaluation of rhesus macaques infected with Leishmania major

Cutaneous leishmaniasis, a parasitic infection causing ulcerating skin lesions, is an important disease worldwide and urgently requires a vaccine. Animal models that closely mimic human disease are essential for designing preventive vaccines against Leishmania major. We have evaluated both biologic and immunologic parameters of cutaneous L. major infection in nonhuman primates. Na?ve rhesus macaques or monkeys previously exposed to L. major were infected with varying doses of L. major metacyclic promastigotes, and lesion size was assessed over a 10-week period. Monkeys previously infected with L. major had much smaller lesions that resolved faster compared with those of na?ve monkeys in response to the two higher doses of infection. Moreover, eight of nine na?ve monkeys had parasites detected in their lesions during the course of the infection. In addition, the cellular infiltrate within the lesions was qualitatively and quantitatively different in na?ve versus previously infected monkeys. Finally, an ELIspot assay determined that the magnitude and kinetics of responses differed between previously infected and na?ve monkeys.     

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

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

Isolation of the novel agent from human stool samples that is associated with sporadic non-A, non-B hepatitis.

The agent(s) responsible for sporadic non-A, non-B hepatitis in humans was serially transmitted in rhesus monkeys by intravenous inoculation of the stool extract from a patient. A novel agent called HFV (hepatitis French [origin] virus) was present as 27- to 37-nm particles in the infectious stool extract. Hepatopathic lesions were noticed in infected monkeys during the acute phase of illness. The purified viral 27- to 37-nm particles consist of a double-stranded DNA of approximately 20 kb and are detected in infected monkey liver. Analysis of cell culture detects the approximately 20-kb-long viral DNA in stool samples from infected monkeys and sporadic enteric non-A, non-B hepatitis patients. Furthermore, the 27- to 37-nm viral particles were able to protect monkeys challenged with infectious stool extract. Our results indicate that 27- to 37-nm virus like particles are responsible for sporadic non-A, non-B hepatitis in rhesus monkeys.     

Experimental infection of rhesus and pig-tailed macaques with macaque rhadinoviruses

The recognition of naturally occurring rhadinoviruses in macaque monkeys has spurred interest in their use as models for human infection with Kaposi sarcoma-associated herpesvirus (human herpesvirus 8). Rhesus macaques (Macaca mulatta) and pig-tailed macaques (Macaca nemestrina) were inoculated intravenously with rhadinovirus isolates derived from these species (rhesus rhadinovirus [RRV] and pig-tailed rhadinovirus [PRV]). Nine rhadinovirus antibody-negative and two rhadinovirus antibody-positive monkeys were used for these experimental inoculations. Antibody-negative animals clearly became infected following virus inoculation since they developed persisting antibody responses to virus and virus was isolated from peripheral blood on repeated occasions following inoculation. Viral sequences were also detected by PCR in lymph node, oral mucosa, skin, and peripheral blood mononuclear cells following inoculation. Experimentally infected animals developed peripheral lymphadenopathy which resolved by 12 weeks following inoculation, and these animals have subsequently remained free of disease. No increased pathogenicity was apparent from cross-species infection, i.e., inoculation of rhesus macaques with PRV or of pig-tailed macaques with RRV, whether the animals were antibody positive or negative at the time of virus inoculation. Coinoculation of additional rhesus monkeys with simian immunodeficiency virus (SIV) isolate SIVmac251 and macaque-derived rhadinovirus resulted in an attenuated antibody response to both agents and shorter mean survival compared to SIVmac251-inoculated controls (155.5 days versus 560.1 days; P < 0.019). Coinfected and immunodeficient macaques died of a variety of opportunistic infections characteristic of simian AIDS. PCR analysis of sorted peripheral blood mononuclear cells indicated a preferential tropism of RRV for CD20(+) B lymphocytes. Our results demonstrate persistent infection of macaque monkeys with RRV and PRV following experimental inoculation, but no specific disease was readily apparent from these infections even in the context of concurrent SIV infection.     

Experimental congenital disease with simian cytomegalovirus in rhesus monkeys

Cytomegalovirus (CMV) infections occur worldwide and are responsible for severe damage to the child in from one to five newborns per 20,000 births. Animal models of congenital CMV infection resulting in disease have been developed in mice and guinea pigs. We report here the development of ventricular dilatation and leptomeningitis in rhesus monkeys, Macaca mulatta, following intrauterine infection with rhesus cytomegalovirus (RCMV). Central nervous system (CNS) lesions were associated with low cytomegalovirus fluorescent antibody titers in affected fetuses. In several infected animals, RCMV was isolated at necropsy from neural and nonneural tissues taken shortly after birth. This model allows investigators to study the pathogenesis and prevention of CNS changes following RCMV infection.