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Disease Dissemination by Vehicles

(44) There is no doubt that vehicles which carry pigs, particularly those that carry slaughter pigs to the abattoir, pose a serious risk, so do vehicles picking up dead pigs for disposal. The risk from feed lorries is less but should not be ignored.

It is obvious that a truck driver unloading pigs at slaughter immediately after diseased pigs have been unloaded from a previous lorry, is likely to contaminate his boots and his lorry. Even if he washes the inside of his truck thoroughly and disinfects it he cannot be sure that he has eliminated all the contaminating disease organisms, including those in his driver's cab. When he calls at the next farm to collect pigs and helps to load them he may well contaminate the loading area and hence the herd. It is amazing how on many farms the water from the surface of the loading ramp drains directly back into the farm. Field experiences have documented two herd breakdowns with swine dysentery due to this. Cross-contamination between herds is also likely when trucks are picking up slaughter pigs or weaners from several different herds to make up a full load for delivery. It was shown in the UK that pig trucks were major factors in the spread of both TGE virus and swine vesicular disease (SVD) virus so it is likely to be true for other pathogens, particularly highly infectious ones.

Evidence for the spread of infectious disease by feed lorries is hard to find. In the USA it is thought that some farmers may carry grain to the local mill in farm vehicles that they have also used to carry pigs and that this is one source of contamination with TGE. It is the common practice of small mills to turn feed around quickly and therefore there is sufficient time for the virus to remain active. Storage would reduce this method of spread. The risk of a bulk feed lorry transmitting faeces-borne diseases on its wheels is very small but could occur over short distances. Diseases such as transmissible gastro-enteritis, porcine epidemic diarrhoea, swine dysentery, salmonellosis and swine vesicular disease might, in theory, be spread in this way. To maintain a vehicle dip to the required strength of a specific disinfectant is a costly procedure. The risks versus costs of this must be equated against the reduction in the amount of contamination on the lorry wheels as it travels along the roads together with the washing and the further diluting effect of a water dip. In general wheels are a negligible risk compared with other aspects of vehicular spread and wheel dips give a false sense of security. Of greater risk however, is the feed pipe that attaches the lorry to the bin. This is carried from farm to farm and often becomes heavily contaminated with faeces. Each farm therefore, should have its own connecting pipe particularly where the bins are not sited to the exterior of the farm. The siting of feed bins to the outside perimeter of the unit obviously reduces the risk.

The question is often asked "How long should a vehicle be left empty after the transportation of other pigs before the transportation of Defined High Health Status pigs (DHHS)?" This will depend on the diseases that the conventional pigs are thought to have, how thoroughly the vehicle is cleaned, the disinfectant used and the disease organisms that contaminated the vehicle.

As a guide:

  • Remove all equipment and partitions from the vehicle.
  • Completely remove all bedding and faeces.
  • Soak the internal surfaces in water and detergent for at least 1/2 hour at a temperature of 50 C
  • Pressure wash with hot water or use a steam cleaner.
  • Pressure wash the exterior of the vehicle.
  • Examine the efficiency of the above procedures. Repeat if there is visual contamination.
  • Finally spray both internal and external surfaces with a non corrosive rapidly acting approved disinfectant such as Virkon S at recommended levels.
  • Document the cleaning procedure. This is important from a legal point of view.
  • If the vehicle is to transport DHHS pigs it must stand empty for 12 hours at least after disinfection provided the health status of the last occupying pigs was known. If not the period should be extended to at least 48 hours depending on the conditions of storage of the vehicle.
Problems can arise in countries during the winter when temperatures remain below freezing for long periods. Under such circumstances facilities must be made available to carry out efficient washing and disinfectant procedures and holding the vehicle in an equitable environment not subjected to freezing.

A loading bay should be provided at the exterior of the farm and it should have the following features:

  • Easily cleaned.
  • Located well away from the unit perimeter.
  • A contact bell.
  • Instruction signs.
  • Clear instructions for drivers.
  • Facilities for the lorry driver to change boots and coveralls.
  • A narrow passage for him to get around behind the pigs.
  • Separate boots and coveralls for any farm personal working outside the unit.
  • A pig passage way leading to it from the pig buildings or a system of one-way doors.
  • It should be elevated to mid lorry height unless the lorry has hydraulic loading facilities.
  • No bedding should be used on the ramp and water should be available for washing and disinfecting after loading.
  • The loading ramp should drain away from the farm to a soak away or sealed tank.
  • A specified approved disinfectant should be used that has rapid activity.
  • There should be a holding area near the vehicle, gated off from the farm, so that pigs can be moved onto it without farm personnel entering.

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