Sunday, 24 January 2010

TB or not TB

Tuberculosis in cattle is mostly caused by the bacteria Mycobacterium (M.) bovis. To fight this bacteria is hard because it lives both intra- and extracellular (not all antibiotics reach the intracellular level. Next to this the bacteria is able to mutate (change) quickly, effective antibiotics are suddenly useless. The bacteria has turned resistant to the antibiotic used by us.

The Netherlands is still officially free of tuberculosis. This doesn’t mean that imported animals aren’t a threat. But these animals are being found by “track and trace’ and destroyed (including animals that have been in contact with these animals). Further spread of M. Bovis is prevented by these measurements.

The danger of alpacas is actually the screening (skin) test (obliged when importing an alpaca) used to identify a bTB infection This test isn’t sensitive and specific enough for alpacas (and certain other animalspecies). This means that there will be false-negative results (false-positive doesn’t seem to happen that much in alpacas). An alpaca does have the M. Bovis bacteria but the test isn’t showing it. This fact could be very harmful for our alpacaherd.
The best test to diagnose TB in your alpaca is a chest X-ray . Laesions in the lungs are found in an early stage.
Laboratoria are trying to develop a bloodtest that recognises specific DNA-material (PCR-test) of the M. Bovis bacteria. So far with unsatisfactory results.

How is bTB spread?
In southern England bTB is a major problem. The badgerpopulation seems to be infected with TB and badgers are thriving well in the UK. New infections take place because of badgers roaming around the area. Different actions are being proposed to deal with the infected badgerpopulation, from vaccination of all badgers (sounds impossible) to shooting badgers to halt the spread of TB.
When the infection is worsening in an animal, inflammatory lesions (tubercle) are being formed in the lungs. When these lesions burst the bacteria is free to leave the animal through the airway (coughing). The environment is infected and another animal can pick up the bacteria. This is the main infectionroute, but the bacteria is also excreted through faeces.
An infected animal isn’t a sick animal. The bacteria can hide itself (latent infection). It may take months before an animals shows any symptoms, usually when the animal is in a stressful situation (labor, transport, show, parasitic infection etc).
In cattle the tuberculinationskintest is usually positive when an animal has been in contact with M. Bovis (no illness symptoms necessary). Unfortunately it doesn’t work that good in alpacas. Too many false negative results.

bTB symptoms
Symptoms aren’t shown till the illness is in its last stage. What symptoms and the severity depends on location of the inflammatory lesions. And usually very aspecific.
Weightloss and a hard dry cough (if the lungs are severely damaged), but this doesn’t mean it is TB. Lots of other diseases can cause these symptoms as well.
Further diagnosis by X-rays in living animals to check on tubercles in the lungs. Or autopsy is necessary to diagnose cause of death.

Therapy and prevention
As mentioned before the bacteria can settle itself intracellular. Rifampicine and possible enrofloxacine (both antibiotics) are suitable to treat tuberculosis. BUT treatment is longlasting (6 months) and therefore very expensive. And there is no guarantee the animal will recover and how much scarring tissue is present in the lungs (this is irreversible). In the Netherlands it is not allowed to treat animals, they should be destroyed (because of the bTB free status). In the UK it is possible to start a treatment when an alpaca is diagnosed or suspected of bTB. As in the Netherlands, alpacas in the UK aren’t qualified as livestock. This means that the livestock law doesn’t include the alpaca.
The author’s opinion is that the dutch regulating authorities aren’t experienced enough with this bTB in alpacas and it misapplies the EU legislation concerning this matter.
For me it doesn’t seem wise to let bTB animals alive. Positive X-rays next to positive tuberculination test should mean putting the animal down as soon as possible and have it autopsied.
When positively diagnosed (culture / Ziehl Neelsen staining), all animals on the farm should be X-rayed. All positive animals should be euthanased to prevent further spreading.
De stalls of the contaminated farm should be cleaned and disinfected on a regularly basis.
If need be heat treatment or UV-radiation, ethanol 70% or formaldehyde to fight the bacteria in the surroundings.

A notification?
Tuberculosis in alpacas is a notifiable contagious disease because of the danger to people (zoonosis). At the moment there is no registered TB skintest with a correct expiration date available (see authors own experiences with the TB skintest of the government!). The government itself is thereby in violation of applying a correct TB skintest. As previously mentioned, the Netherlands is officially free of bTB.

Advice & Discussion
Autopsy should always be performed on a dead alpaca, especially when symptoms included weightloss, respiratory problems and fever.

View Author
Because of the Dutch free bTB-status it is clear that bTB in the Dutch cattlepopulation hardly plays a role here in the Netherlands. But alpaca owners should be aware of the risks of importing alpacas (especially from higher risk areas). And the owners should act responsible towards the whole alpaca herd and human health by reporting sick, of bTB suspected animals and perform autopsy on animals that have died on the premises.
The only just method to protect your herd against bTB is X-rays. In an attempt to detect the disease as early as possible and fight the bacteria.
Animals attending a show should be stationed per region, to prevent further spreading throughout the country. Closed fencing to avoid direct contact between animals from different breeders and minimize a chance of bTB spreading

For now the risk of bTB in the Netherlands seems no issue. Especially, because the slaughter line of cattle is continuously monitored (not alpacas, this should be our own responsibility as a breeder).

Leo J.H. van Merwijk – DVM
Bata4en – Animal Hospital

1 comment:

  1. Very interesting thanks. We are TB free in Scotland which makes things difficult re movements etc. The situation in England is worrying for us all in the UK.


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