Ismat Perveen Ahmed ( Microbiology, Vertebrate Pest Control Laboratory, University Campus, Karachi-32. )
Prevalence of agglutinating antibodies against certain leptospiral serotypes were investigated in man, domestic animals and rodents of Pakistan. In man L. grippotyphosa (14.2%), in cow L. pomona (50.9), in buffalo L. pomona (20.0%), in sheep L. australis (51.4%), in goat L. pyrogenes (30.7%) in R. norvegicus L. grippotyphosa (65.2%) and in Suncus murinus L. grippotyphosa (20.0%) were found as most prevalent serotype. The overall leptospira prevalence rate in commensal rats (A. rattus and ft. norvegicus) were determined 100%. The result suggested that the rodents and Suncus murinus play main role in transmission of leptospirbsis in man and livestock (JPMA 37 : 233, 1987).
Leptospirosis is one of the most wide spread zoonosis. The most important serotype L. icterohaemorrhagiae is wide spread and encoi.mtered in most parts of the world in man and animals.1,8
Leptospirosis. primarily parasites of vertebrates other than human beings, such as rodents, dogs, pigs and cattle, in which the bacteria persist throughout life as asymptomatic infection of the kidney9,14. These infected animals continuously shed leptospira in the urine. Human infection results when a person becomes infected through skin contact with urine from an infected animal or by exposure to tirine contaminated water or soil. The organisms enter the blood and then invade various tissues and organs, particularly
the kidney, liver, meninges and conjunctiva. The clinical manifestations of human leptospirosis vary considerably. It may be a mild influenza-like illness or a severe or fatal disease characterized by jaundice.
Rodents have been recorded to be carriers of leptospires throughout the world and are important reservoir of infection for man and live stock. The role of the rodents as a source of leptospiral transmission is important yet little attention has been paid in Pakistan. In this serological investigation, leptospiral antibodies were detected in. man, domestic animals, rodents and Suncus murinus (Insectivora) which suggested the prevalence of leptospiral infection in Pakistan.
MATERIAL AND METHODS
Rodents were trapped from different habitats including residential areas, wheat and rice godowns, agricultural fields and sandy desert areas. These rodents were brought alive in cages and cardiac blood taken in Vertebrate Pest Control Laboratory. Blood of domestic animals were collected from slaughter house and human blood from Karachi hospital.
All blood sera were preserved at ‘20°C for the serological investigation and tested for the presence of leptospiral antibodies using rapid macroscopic slide agglutination test. 15 All undiluted sera were first screened serologically by using four pools of antigens as indicated below.
Pool 1. L ballum, L. canicola, L. icterohemorrhagiae.
Pool 2. L. bataviae, L. Grippotyphosa, L. pyrogens.
Pool 3. L. autumnalis, L. pomona, L. woiffli.
Pool 4. L. australis, L. Hyos, L. mini, Georgia.
Positive reactions with any of these pools were then checked by using the formalized suspensions of individual leptospira serotype antigens, comprising the positive pooi. A result was considered positive when 50% agglutination was observed.
Sera of 56 human beings, 55 cows, 60 buffaloes, 35 sheep, 65 goats, 290 rodents and 20 house shrew (Suncus murinus) were tested serologically for the presence of leptospiral infection. Prevalence of leptospiral antibodies were found 25%, 92.7%, 81.6%, 94.2%, 81.5%, 68.2% and 20%, respectively (Table-I).
Rodent species were studied for the presence of leptospiral antibodies. The commensal rats (R. rauus and R. norvegicus) showed 100% infection rate. The rodent species T indica 90.0%, M. hurrianae 6 1.8%, B. bengalensis 20.0% N. indica 40.0% and M. meltada 24.0% were also found seropositive. These rodents were trapped from agricultural areas and grain godowns, which represents threat to farmers and their live stock (Table-II).
Seven leptospiral serotypes were investigated in positive sera of man and animals. L. grippotyphosa was found most prevalent serotype in rodents, house shrew, domestic animals and man. 65.7% R. norvegicus and 63.6% R. rattus were found seroposifive L. pomona, L . australis and L. pyrogens antibodies were detected from rodents and domestic animals. 50.9% cows were found seropositive to L. pomona and 45.4% to L. wstralis; 22.8% sheep and 30.7% goats were found seropositive to L. pyrogens . L. canicola and L. ballum were found as least prevalent serotypes and detected only in rodents sera. L. icterohemorrhagiae antibodies were found in rodents, domestic animals and human sera. This serotypes cause Well’s disease in man. 10.7% of human sera were found positive to L. icterohaemorrhagiae serotype (Table-III).
Each leptospiral serotype has its own particular animal host, usually a rodent species.
Domestic animals, dogs and pigs also act as natural reservoirs. In localities where different species of rodents and animals exist together, as in agricultural fields and areas where abundant food supply are available as in grain storage, one serotype of leptospira may be carried by different animal species and one species of animal may be infected with more than one leptospiral serotype. Rodent species R. norvegicus and R. ratius have a cosmopolitan distribution and many different serotypes have been isolated from these species in other countries12.
The results indicate that the commensal rodents are mainly responsible for the transqiission of L. icterohemorrhagiae and L. grippotyphosa infection in man and domestic animals. These commensal rodents commonly act as carriers and transmit the organism to others. Man, when infected, does not ordinarily transmit the organism to other human or animal host. Domestic animals become infected through grazing in fields or from fodder contaminated with rodents urine and infection may then be transmitted from animal to animal. it is observed that rodent’s species which are mainly found in agricultural areas and have close contact with domestic animals act as carrier and transmit L. australis, L. pomona and L. pyrogens infection in livestock.
Only few rodent species were found sernpositive to L. canicola and L. ballum. This indicates that when there is a high level of other serotype infection in rodents the prevalence of L. canicola or L. ballum serotype infection is low.
In this study Suncus murinus ( Insectivora) commonly found with commensal rats was found seropositive to only L. grippotyphosa but it has been reported to be host to a wide range of leptospiral serotype.16 It is suggested that this may also play a role in transmission of leptospirosis through urine contamination of foodstuff.
It is concluded that workers in sugarcane and rice field, farmers in agricultural area, fishermen, sewer workers and butchers represent high risk group as they are more exposed to infected animal and moist conditions allow the leptospires to survive for a considerable time outside the animal body.
The author is grateful to M.M. Shafi, Project Director, Vertebrate Pest Control Laboratory, Karachi, for facilities provided during this investigation. Field and Technical assistance rendered by Zafar All, Mohd. Aslam and Mohd. Ghaffar, Assistants V.P.C.L. are also acknowledged.
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