Legionella and legiollosis: an overview and a preliminary study in Kenya.
Anurag, Phakke B V M
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Several Legionella species have been recognized as human pathogens for more than a decade. The manifestations of legionellosis vary from asymptomatic seroconversion or mild febrile illness to severe, fatal pneumonic disease with multiple system failure. Because of this wide clinical spectrum legionellosis probably goes unrecognized especially if it occurs where it is not suspected. The distribution of Legionella appears to be world wide, and retrospective serological investigations have revealed the presence of Legionella infections long before the first isolation of these organisms. Adequate information is not available on the distribution of legionellosis on the African continent. While readily recognized as a human infection, there is hardly any mention of legionellosis in domestic or wild animals in spite of the apparent wide distribution in some regions of these organisms in natural or man-made water sources. Consequently, more information is needed on the geographical distribution of these infections, the susceptibility of various animal species and the reservoirs. potential cases of legionellosis as well as of recognized sources may provide this information. Although natural Legionella infections have not been reported in animals, experimentally induced infection has succeeded in a variety of animal species. The presence of naturally occurring Legionella antibodies in animals would suggest that these animals are susceptible to Legionella infection. With the assumptions that the main reservoirs and sources of infection are natural or man-made water sources, and that a variety of animals are susceptible to Legionella infection, it would appear consequential that animals might serve as seniinels -for the presence of these organisms in a given environment. Demonstration of significant antibody titres to Legionella would only be indicative of their presence in the environment, and confirmation would have to be obtained by isolation and identification. A vast literature on Legionella and legionellosis has been published in the last few years. In this study an attempt has been made to provide a fairly comprehensive review of the literature. Investigations were carried out to establish the presence or absence of Legionella by testing animal and human sera for significant levels of antibody titres, and also by attempting isolation of these organisms from environmental sources. Serum samples from cattle, sheep, goats, pigs, horses, camels, dogs, wild animals, healthy humans and human pneumonia cases were titrated using the microagglutination test for antibodies to~. pneumophila serogroups 1-6, ~. longbeachae serogroups 1 and 2, ~. bozemanii, L. dumoffii, L. gormanii, ~. micadadei and~. jordanis. Although the serum samples were not randomly selected, they represent nevertheless populations from several geographic areas of the country. The majority of the serum samples from all species showed agglutination ,reactions up to a dilution of 1/16 to all Legionella antigens. It is unlikely that these reactions are indicative of exposure to all the Legionella strains. However, antibody titres in the range 64-512 to at least one Legionella species or serotype were found in 25/168 (14.9%) cattle, 5/148 (3.4%) sheep, 18/204 (8.8%) goats, 2/107 (1.9%) pigs, 2/19 (10.5%) horses, 2/65 (3.1%) camels, 6/51 (11.8%) dogs, 1 eland out of 10 elands from a total of 196 wild animals, and, 3/224 (1.3%) human serum samples. Most investigators would consider titres in this range indicative of infection. In the present study, however, titres above a value of four times the estimated means of the titre (xvii) distributions were considered indicative of infection, or possibly due to exposure to organisms sharing antigens with Legionella. The lowest titre which was considered suggestive of infection would therefore vary not only between animal species but also with the antigens. While in most animals and humans the titres to most Legionella antigens had a monophasic distribution, cattle sera gave biphasic distributions to~. pneumophila serogroup 3 and 6, and to L. jordanis. The second peak appears to constitute a distinct population of animals which have suffered past infection. Although some cattle sera gave titres to~. pneumophila serogroups 1 and 5, and to L. bozemanii, which fe~l within the range of the first peak, the titres were sufficiently high to warrant their inclusion among positive reactors. Sheep sera gave elevated titres to L. pneumophila serogroup 2, ~. bozemanii, ~. dumoffii and~. jordanis. Goat sera showed elevated titres to L. pneumophila serogroups 2,4, and 5, L. bozemanii, L. dumoffii and ~.jordanis. A few of the sera from dogs, horses and camels gave titres to L. pneumophila serogroup 2, or L. bozemanii or L. jordanis, which may be significant. (xviii) All sera from pigs and wild animals gave only low titres which were not considered significant. Seven of 224 sera from healthy humans gave titres in a range which may indicate past exposure to ~. pneumophila serogroups 1,3,5 and 6. Only one of 29 human pneumonia patients showed a titre of 32 to~. pneumophila serogroup 3. Although of possible significance, this could not be ascertained since a second sample could not be obtained for confirmation. In spite of the serological evidence for possible expsoure to several Legionella species in a variety of animals, it cannot be excluded that these observations may be due to exposure to cross-reacting organisms, such as certain strains of Pseudomonas fluorescens, Pseudomonas alcaligenes, Pseudomonas maltophila, Bacteroides fragilis, Flavobacterium sp.and Xanthomonas sp. Cross-reactions have also been observed with sera from humans suffering from plague, tularemia and leptospirosis. Leptospirosis may be particularly relevant in Kenya since the infection has been documented in several geographic areas of the country. To conclusively demonstrate the presence of Legionella, attempts were made to isolate the organisms. A total of 41 water samples from evaporative condensers, cooling towers, rivers, streams and ponds in the Nairobi area and from Lake (xix) Victoria, were tested. These water samples were selected from water sources similar to those which had been found to yield Legionella in other parts of the world. Although the procedures used for the examination of water samples were identical to those recomended by previous investigators, none of the 636 bacterial isolates initially suspected to be Legionella could be confirmed as such upon further examination. Although the results of the serological investigations are indicative of the presence of ~. pneumophila serogroup I to 6, ~. bozemanii, ~. dumoffii and L. jordanis, it has not been possible to demonstrate conclusively the presence of these organisms in.Kenya, neither as causative agents of infections in man or animals, nor as free-living organisms in the environment.