Wild Reservoir Hosts Research Articles

ECOLOGY OF THE LEISHMANIA SPECIES IN THE GUIANAN ECOREGION COMPLEX

In the Guianan ecoregion complex, at least seven Leishmania species belonging to both the L. (Leishmania) Saf' janova, 1982 and L. (Viannia) Lainson and Shaw, 1987 sub-genera are causative agents of American visceral leishmaniasis, mucocutaneous leishmaniasis, and cutaneous leishmaniases, including localized and diffuse forms. They are mostly sylvatic species subjugated to their own specific Lutzomyia sand fly vectors and to particular wild mammalian reservoir hosts of the dense rain forest. Originally implicated strictly in wild zoonoses and developing in forested ecotopes, Leishmania show a particular adaptive plasticity to face environmental modifications following deforestation and anthropization. This review presents the different pathogenic complexes of these parasites, emphasizes their implication in human diseases, and considers the influence of humans on their ecology.

Impact of leishmaniasis on public health

Leishmaniasis is a parasitic zoonosis caused by protozoans of the genus Leishmania transmitted by insects known as phlebotomines, which are found in wild or urban environments. It affects domestic and wild animals and transmission to man happens by accident. The disease occurs in tropical and sub-tropical areas, mainly in Asia, Europe, Africa, and the Americas. There are two forms that affect man: American cutaneous leishmaniasis (ACL) and American visceral leishmaniasis (AVL). The latter is caused by three species of Leishmania: Leishmania (Leishmania) donovani, Leishmania (Leishmania) infantum, and Leishmania (Leishmania) chagasi, which are grouped in the Leishmania (Leishmania) donovani complex. Wild reservoir hosts of L. chagasi known so far are foxes and marsupials. In domestic environment, dogs are the most important reservoir hosts and sources of infection to the vectors Lutzomyia longipalpis. Leishmaniasis is difficult to control, causing epidemic outbreaks, thus being an important public health problem. Due to lesions caused by the mucocutaneous type and the severity of those caused by the visceral type in humans, visceral leishmaniasis is one of the main public health concerns. This paper is part of the monograph presented at the end of the residency program in the field of Zoonosis and Public Health at the School of Veterinary Sciences and Animal Husbandry, Sao Paulo State University, UNESP, Botucatu, Sao Paulo State, Brazil, in 2005.

Control measures for some important and unusual goat diseases in southern Africa

The paper comprises an overview of important or unusual goat diseases occurring in southern Africa, with the emphasis on current effective disease control measures and recent developments in this field. The diseases are dealt with under four headings: (1) Infections; (2) Parasites; (3) Plants and nutrition; (4) Genetic and other conditions. In each section, the following are given more prominence: (1) Heartwater, certain clostridial diseases, pasteurellosis, abscessation and orf; (2) Haemonchosis, coccidiosis and certain ectoparasites; (3) Redgut and phytobezoars; (4) Abortions, postnatal mortality, exposure, predation and swelling disease. The major diseases of helminthosis and heartwater are dealt with at greater length. Helminth control currently concentrates on individual treatment of badly affected goats, rather than mass treatment. This lowers the selection rate for worms resistant to anthelmintics. A break with the old policy of “treat-all-and-move” is advocated for the same reason. The use of the FAMACHA © system (clinical anaemia evaluation) for haemonchosis control in goats is explained and the potential of body condition scoring for identifying animals heavily infected with other pathogenic helminths is highlighted. Replacement of highly resistant worm populations by a dilution method is outlined and several practical measures for managing worms in goats are given. The control of heartwater is determined by epidemiological and risk factors, comprising those affecting the vector (climate, season, vegetation, wild reservoir hosts, tick control), the organism (strain virulence, infection rate of vectors), and the host (species, age, breed, genetic resistance and immune status). In circumstances of very low infection risk, surveillance and treatment is recommended. In higher risk situations, strict tick control or zero grazing may be the best option. In endemic areas, immunity is the preferred and most reliable approach. This is achieved by exposure to infected ticks, vaccination and animal selection. Details of these options and their practical implementation are given.

A peridomestic population of the tsetse fly Glossina palpalis palpalis Robineau-Desvoidy, 1830 (Diptera: Glossinidae) at Kontagora town, Niger state, Nigeria

The present article considers some aspects of a peridomestic population of the tsetse fly Glossina palpalis palpalis Robineau-Desvoidy, 1830 in Kontagora, Nigeria. This situation characterizes an abnormal behaviour of the vector, and it is of significant epidemiological importance. Data on the ecology of this species were collected in 1995 and 1999. The results indicated that the species exists during both dry and wet seasons; approximately 30.0% of the catches were gorged with blood giving a MHS of 2.4, indicating a well-nourished population. Dissection of inseminated pars indicated pregnancy rates of approximately 30.0% and 70.0% in the dry and wet seasons and the presence of all 4 stages of pregnancy, suggesting that breeding occurs at both seasons. Longevity of flies was approximately 16 days in dry season and 25 days in the wet season. Overall results indicated that vector/host contact was high and the fly population has adapted and actively breeding in the area. Trypanosome infection rates of 18.2% consist of 1 brucei-type and 5 vivax-type infections. The public health implications of the close proximity of the wild natural reservoir hosts of the human T. b. gambiense Dutton, 1902 parasites at the Kainji Wild Life park is discussed.

The isolation of Leishmania tropica and L. aethiopica from Phlebotomus ( Paraphlebotomus) species (Diptera: Psychodidae) in the Awash Valley, northeastern Ethiopia

In a survey of Leishmania infections in phlebotomine sandflies in a highly suspected focus of leishmaniasis in the Awash Valley (northeastern Ethiopia) between January 1994 and August 1997, a total of 3307 females of 11 Phlebotomus species ( P. orientalis, P. fantalensis, P. saevus, P. sergenti, P. gemetchi, P. alexandri, P. bergeroti, P. duboscqi, P. arabicus, P. martini, and P. rodhaini) were dissected. Promastigotes were detected in 17 females of three species (11 P. saevus, 4 P. sergenti and 2 P. arabicus). Of these, only two P. saevus (one from Upper Awash and one from Middle Awash) and three P. sergenti (from Upper Awash) positives were successfully isolated in culture and were typed by isoenzyme analysis. Four isolates (two each from P. saevus and P. sergenti) were identified as new zymodemes (Z) of L. tropica and one isolate from P. sergenti was typed as a new zymodeme of L. aethiopica. This is the first finding of natural infections of P. saevus and P. arabicus and the first evidence for the former to be a vector of L. tropica. This is also the first time P. sergenti has been implicated in L. tropica transmission in Ethiopia; the isolation of L. aethiopica from a Paraphlebotomus species ( P. sergenti) is also a new record. The possible presence of human cutaneous leishmaniasis ( L. tropica and L. aethiopica), and wild reservoir host(s) of the parasites, especially rock hyrax ( Procavia capensis) in the Upper and Middle Awash Valley remain to be determined.

Natural nidality in Bolivian hemorrhagic fever and the systematics of the reservoir species

Zoonoses within wild reservoir host populations often occur focally obeying Pavlovskii’s rules of “natural nidality”. What appears to be a clear example is Bolivian hemorrhagic fever (BHF), a disease endemic to northeastern Bolivia. The etiological agent is Machupo virus (MACV, Arenaviridae). The vertebrate reservoir, identified 30 years ago, was Calomys callosus a wild rodent common to open biomes in the lowlands of southeastern South America. The lack of concordance between the occurrence of MACV and the range of its rodent host has puzzled cadres of researchers and could be used as an exemplar of natural nidality. Here, we show that the populations of rodents responsible for the maintenance and transmission of MACV are an independent monophyletic lineage, different from those in other areas of South America. Therefore a clearer understanding of the systematics of the host species explains the apparent natural nidality of BHF. Similar studies may prove to be informative in other zoonoses.

A longitudinal study of an endemic disease in its wildlife reservoir: cowpox and wild rodents

Cowpox is an orthopoxvirus infection endemic in European wild rodents, but with a wide host range including human beings. In this longitudinal study we examined cowpox in two wild rodent species, bank voles Clethrionomys glareolus and wood mice Apodemus sylvaticus, to investigate the dynamics of a virus in its wild reservoir host. Trapping was carried out at 4-weekly intervals over 3 years and each animal caught was uniquely identified, blood sampled and tested for antibodies to cowpox. Antibody prevalence was higher in bank voles than in wood mice and seroconversion varied seasonally, with peaks in autumn. Infection was most common in males of both species but no clear association with age was demonstrated. This study provides a model for studying other zoonotic infections that derive from wild mammals since other approaches, such as one-off samples, will fail to detect the variation in infection and thus, risk to human health, demonstrated here.

Natural infections of Leishmania peruviana in animals in the Peruvian Andes

Evidence that domestic dogs may act as reservoir hosts for cutaneous leishmaniasis in the Peruvian Andes is provided by the isolation, for the first time, from naturally infected dogs of parasites identified (by isoenzymes) as Leishmania peruviana. Leishmania parasites were isolated from nasal aspirates or biopsies from 5 (1·8%) of 279 asymptomatic dogs sampled in endemic villages of the Peruvian Andes. In addition, Leishmania (Viannia) infections were identified in 15 (5·4%) of 276 nasal samples by the polymerase chain reaction (PCR) using subgenus-specific primers. Further circumstantial evidence for a reservoir role for dogs comes from the finding of a relatively high dog blood index among the sandfly vectors collected inside houses (29% for Lutzomyia peruensis and 17% for Lu. verrucarum). Possible wild mammal reservoir hosts for Andean cutaneous leishmaniasis were also detected in endemic villages. At least 8 species were identified among the 1266 small mammals trapped. Leishmania parasites were isolated from blood or skin biopsies taken from 2 (2·6%) of 78 Didelphis albiventris and 6 (1·2%) of 511 Phyllotis andinum. Three isolates were identified by isoenzymes as L. peruviana, and the other 5 were identified by PCR as Leishmania (Viannia) species. Leishmania (Viannia) infections were also identified by PCR directly on skin biopsies taken from 2 (2·8%) of 72 D. albiventris, 1 (0·2%) of 499 P. andinum, and 4 (2·6%) of 153 Akodon sp.

Ecoepidemiological aspects of American cutaneous leishmaniasis in the state of São Paulo, Brazil.

The aim of this study is to review some of the ecoepidemiological aspects of american cutaneous leishmaniasis (ACL) in the State of São Paulo, Brazil. During the first half of this century ACL occurred in São Paulo, predominantly on the bank of the Tietê River, where there were railroad constructions and there was inevitable contact between workers and forested areas. Man's activities resulted in a drastic reduction of the forested regions of the State and molded the present landscape found in São Paulo, which brought a gradual change in the epidemiology of ACL during this century. Currently ACL can be considered as an endemic disease. Nowadays, ACL is found in different regions of São Paulo State, and is no longer limited to the bank of the Tietê River. The disease occurs in all age groups and sexes. Lack of knowledge about wild reservoir hosts of Leishmania (V.) braziliensis has simulated speculation about the possible role played by domestic animals (dogs and equines). Man's activities also favoured Lutzomyia intermedia a sandfly species which can clearly thrive in changed environments. L.(V.) braziliensis continues to be transmitted, even after decades of forest destruction in São Paulo.

Detection of antibodies to Trypanosoma cruzi in the South American opossum ( Didelphis marsupialis)

Stocks of Trypanosoma cruzi belonging to two different zymodemes, one usually associated with silvatic reservoir hosts and the other not normally found in wild reservoir hosts, were used as sources of diagnostic antigens in enzyme-linked immunosorbent assays for the detection of antibodies to T. cruzi in Didelphis marsupialis. Both antigen preparations reacted with antibodies in sera from animals found to be infected by conventional parasitological techniques and also in sera from a proportion of the remaining animals in which it was not possible to detect trypanosomes.

Leishmaniasis in Colombia, a review.

A review is made of 60 publications on leishmaniasis in Colombia reported between 1889 and the present. A serious source of difficulty in interpreting the literature is the frequent discussion of "cases" (1,536 of 1,865, or 82%) that were never confirmed by observation of the parasite or by positive immunological tests. The apparent distribution of the disease is considerably biased by the real distribution of physicians. Nevertheless, laboratory-confirmed cutaneous leishmaniasis has been reported from most humid, lowland regions, and apparently the disease is endemic in nearly all the administrative sections of the country. Mucocutaneous involvement seems to occur in around 25% of the cases. Visceral leishmaniasis is seldom reported and is known to occur only in the Magdalena River basin. There have been no surveys to identify arthropod vectors or wild reservoir hosts, although two naturally infected dogs were associated with one of the visceral leishmaniasis cases. Leishmaniasis is a seldom diagnosed but major health problem in several regions of Colombia, in terms of the number of persons affected and the difficulty of obtaining treatment.