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Transmission of Mycoplasma Dispar among a Succession of Newborn Calves on a Dairy Farm

Spridning av Mycoplasma dispar hos en serie nyfödda kalvar i en mjölkbesättning

Abstract

Transmission of Mycoplasma dispar among 33 newborn calves (nos. 1–33) on a dairy farm, transferred in order of birth into individual pens in a separate calf rearing room during a period of 50 days, was investigated. The first calf (no. 1) was deliberately infected. Weekly nasal swabs were taken 9 times.

Twenty-eight susceptibles (data for 4 calves are excluded because of omissions in sampling) were found to be positive for M. dispar on average 8.6 days (the range 5 to 15 days) after the start of exposure. Among the first 7 (nos. 2–8) and the latter 21 susceptibles (nos. 9–10 and 15–33), the infection was first detected on average after 12.1 and 7.4 days, respectively. The interval measured (from the start of exposure to the first detection of infection) comprised 3 parts: the transmission time proper, the latent period and the delay in detection of positivity due to the sampling interval. The variation affecting the first 2 parts of the measure, and especially the transmission time, clearly must account for the above difference between the 2 study phases; an association with the density of infective calves was apparent. The last component of the measure was distributed randomly and its lenghtening effect on the figures was estimated at 2 to 3 days. By subtraction, the average period preceding detectable colonisation in the latter part of the study was approximated as 4 to 5 days. Through another approach, estimation by Reed-Muench calculation, the figure was 4.7 days. The existing knowledge of the usual lengths of latency - with the present limited variation among the intervals measured - indicates that the lag in transmission, i. e. the transmission time proper, in the latter phase of the study was unlikely to exceed a few hours; the major part of the average 4 to 5 days interval was thus accounted for by latency. The principal mode of transmission was inferred to have been air-borne, sometimes over several meters.

Forty-five adult cows, sampled after the delivery, including most dams of the calves studied, were all negative for M. dispar; M. bovirhinis and Acholeplasma laidlawii were isolated from 8 and 3 cows, respectively.

Sammendrag

Spridning av Mycoplasma dispar bland 33 nyfödda kalvar som i födelseordning flyttades till egna boxar i ett separat kalvuppfödningsrum undersöktes under en 50 dagars period. Den första kalven infekterades med avsikt. Prov från nässlemhinnan togs varje vecka inalles 9 gånger.

Tjugoåtta emottagliga djur (uppgifterna för 4 kalvar lämnades bort p. g. a. försummelser vid provtagningen) visade sig vara positiva efter i medeltal 8.6 dagar (varitionen 5 till 15 dagar) räknat från utsättandet för smittan. Bland de 7 första (kalvarna 2–8) och de senare 21 (kalvarna 9–10 och 15–33) emottagliga djuren fastställdes infektionen efter i medeltal 12.1 och 7.4 dagar i angiven ordning. Den uppmätta tiden bestod av 3 delar: den egentliga spridningstiden, latenstiden och den tekniska förseningen vid isoleringen, som en följd av tidsintervallen mellan provtagningarna. Avvikelsen inom de två första delarna, i synnerhet spridningstiden, förklarar tydligt skillnaden mellan undersökningens ovannämnda två grupper. Ett samband med tätheten av infekterade kalvar var uppenbar. Den sista delen av tidsmåttet fördelades på måfå och dess förlängande effekt på värdena uppskattades till mellan 2 och 3 dagar. Genom att subtrahera ovannämnda värde uppskattades medeltalet för tiden som förgick den påvisade kolonisationen i den senare delen av undersökningen till ca. 4 till 5 dagar. Med Reed-Muenchs uträkning blev värdet 4.7 dagar. Nuvarande kunskap om latenstidens längd visar att fördröjningen vid spridningen, d.v.s. den egentliga spridningstiden i undersökningens senare del, knappast överskred några timmar. Därmed kan största delen av den i medeltal 4 dagar långa intervallen betraktas som latensperiod. En ytterligare slutsats var att den huvudsakliga spridningsvägen är aerogen.

Prov som togs av fyrtiofem kor efter förlossningen inkluderande mödrarna till de flesta kalvarna i undersökningen, var alla negativa med avseende på M. dispar, M. bovirhinis och Acholeplasma laidlawii isolerades från 8 och 3 kor i angiven ordning.

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Acknowledgment

I am greatly indebted to Professor Martti Lampila, Dr. Agr., Head of the Department of Animal Husbandry of the Jokioinen Agricultural Research Centre, for providing the facilities for this study and to the personnel of the Research Centre, especially to Ms. Marja Alaspää, M. Agr. Sc., and Mr. Kalle Saastamoinen for their help and co-operation during the present study. My warmest thanks are also due to Mr. Juha Nousiainen, M. Agr. Sc., for his kind collaboration. This study received financial support from the Research Council for Medical Sciences of the Academy of Finland.

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Tanskanen, R. Transmission of Mycoplasma Dispar among a Succession of Newborn Calves on a Dairy Farm. Acta Vet Scand 28, 349–360 (1987). https://doi.org/10.1186/BF03548603

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Keywords

  • Mycoplasma infections
  • mycoplasmosis in cattle
  • respiratory diseases of cattle
  • epidemiology
  • disease transmission