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Investigating anthrax – On the trail of a rare and deadly disease outbreak

by
01 March 2017, at 12:00am

In October 2015, APHA faced the challenge of tackling a possible case of anthrax that turned out to be a confirmed incident. Anthrax is an acute and usually fatal animal disease caused by the spore-forming bacterium Bacillus anthracis.

Background

In October 2015, APHA faced the challenge of tackling a possible case of anthrax that turned out to be a confirmed incident. This only occurs every 10 to 20 years and cases are mainly linked to historical occurrences. The most recent confirmed case was in 2006, and is described in an article by Arjen Brouwer, Veterinary Adviser to the Welsh Government, in the Government Veterinary Journal (Volume 18, No 1, 2007/8).

Anthrax is an acute and usually fatal animal disease caused by the spore-forming bacterium Bacillus anthracis. The spores of Bacillus anthracis are infectious and can survive in the environment for many years. Human infection is very rare in Great Britain, and there is a very low risk of infection from infected animals, animal products or infected land. All mammals are susceptible, but also some bird species, and the disease is rapidly fatal; therefore affected animals may be found dead without signs of illness.

The incubation period in cattle and sheep could be up to 14 days, although it is usually five to seven days, with an onset of non-specific clinical signs, which may include fever, colicky pains, refusal of food, loss of milk, subcutaneous oedema, among others, although a feature of anthrax infection is failure of the blood to clot. Other species, such as pigs, dogs and horses, exhibit similar signs, but death is not always inevitable, and chronic infection can occur.

This incident occurred in Wiltshire, with two cases ultimately confirmed in dead animals found on 21 and 27 October 2015.

Anthrax investigations: All investigations should be reported to APHA, even reports after 5pm Mon- Fri and at weekends. The telephone number to use is 03000 200 301 and there is an out-of-hours facility on that number for reporting suspicion of disease in animals. An investigation by an OV is not to be undertaken in anticipation of authorisation and not until APHA have instructed accordingly.

When reporting suspicion of anthrax (in normal working hours or out of hours), a history must be taken from the client and passed to the APHA Duty Vet. There may be information in the history which can be used to conclude that it is reasonable to rule out anthrax as the likely cause, e.g. poisoning, lightning strike, or electrocution. The APHA vet would also need answers to the following questions: Is there a history of anthrax on the premises? Have there been there multiple sudden deaths? Has there been recent flooding or dredging/ditching activity, or soil disturbance? Is there black ‘tarry’ blood from the muzzle or rectal orifice?

Initial case: An Official Veterinarian from Wiltshire was notified of the sudden death of a cow, and obtained permission to investigate the case. Following examination of a stained blood smear, the OV requested a consultation with an APHA veterinarian. Dark blue rod chains (not many) could be seen, and some with pinkish capsule, so anthrax could not be ruled out. Following notification to the Veterinary Exotic Notifiable Diseases Unit (VENDU), an APHA vet collected a second set of samples for submission to the specialist laboratory in Porton Down and restrictions were imposed on the premises on 22 October 2015. Emergency response was triggered by the Chief Veterinary Officer and Wiltshire County Council was notified. Following confirmation of disease on the evening of Friday 23 October 2015, as the duty vet on call I was nominated case officer to deal with the incident and liaising officer with the different parties involved (the local authority, Public Health England and the farmer). Also the local authority proceeded with the carcase incineration.

Disposal of carcases: The Anthrax Order 1991, Article 9 states: “The local authority for the area in which the infected place is found shall cause the diseased or suspected carcases to be disposed of by incineration on the infected place or by such other method as the Divisional Veterinary Officer may approve.”

Premises investigated

The premises investigated were occupied by a cattle enterprise: a suckler herd consisting of 350 animals. The herd was kept on two separate farms under the same holding number: the main farm kept 250 cattle (including bulls, cows, calves, heifers and steers) and a second farm, which was used to graze cattle in summer and to produce arable crops, had 96 cattle at the time of the outbreak (49 cows and 47 calves at foot). There was no other livestock on the holding.

The carcases of the suspect animals were found at the second, summer-grazing farm. From early on it was evident that there was a previous history of anthrax on the premises, with episodes in 1996, and in the ’60s, linked to an old tannery and the Biss Brook.

On inspection of the carcases, typical signs of anthrax were found:

  • In the first case, a homebred cow, South Devon, six years old, in good body condition, a trickle of red unclotted blood could be seen coming from nostrils. It was thought that the cow could have been dead for some time but it was reported on 21 October 2015.
  • In the second case, a homebred cow and the leader of the group, a Hereford cross, nine years old, in good body condition, trickles of red unclotted blood were noted coming out from the nostrils and ears. This animal was reported dead 12 hours before inspection on 27 October 2015.

Although there were three groups of cattle grazing on the premises – one of heifers, one of steers and one of cows with calves at foot – only the group of cows and calves was affected. They had been grazing all summer on the southern fields next to the Biss Brook waterway, and then moved to the northern fields four days before the first case was reported, when the first cow was last seen alive. The second case was reported a week later.

Disposal

As per current procedure, both carcases were disposed of on site by the local authority by incineration, using a mobile incinerator. This is a lengthy and laborious process that can take 36 to 48 hours for each carcase. The potentially contaminated soil where the carcases were found was also incinerated.

The ashes resulting from the incineration were still considered hazardous (due to the potential presence of spores, metals and other materials resulting from the cremation), and had to be licensed and disposed of accordingly, using an approved incinerator at Porton Down.

Historical cases: In the course of the investigation in October 2015, the history of anthrax in the Westbury area, and this farm in particular, became clearer. During the 1960s, several farms along the Biss Brook had confirmed cases, presumably associated with the contamination of the brook with waste drainage from the tannery. In addition, reportedly the tannery had imported some infected hides that were later buried on the premises, and the brook had been cleared in 1963. The farm in Westbury was a dairy farm at the time and it had reported at least four suspect cases; all suspect carcases were buried on site. The old tannery, which had been in operation since the 1890s, finally closed in the 1970s.

In 1996, anthrax reappeared at this farm with three carcases reported as suspects, although only two were confirmed. This time the carcases were incinerated on site, rather than being buried. This incident was associated with a number of possible sources including soil disturbance of the northern bank of the brook, historical burials, irrigation (which at the time brought worms up to the surface) and digging activity in the area of the tannery due to the construction of a new housing estate.

Epidemiology

Following confirmation of the first case, as case officer I conducted a full epidemiological investigation, including gathering information on the site where the animals died, to feed various risk assessments carried out by the specialist epidemiology team. Conversations early on in

the investigation included the potential vaccination of the remainder of the herd to contain the spread of disease, although this was eventually ruled out, as no further cases were reported.

All possible routes of infection were considered, including the old burial sites, movements of animals, materials and equipment and soil disturbance on the premises. Potential infection sources off the premises, such as digging activity upstream and contaminated river banks were also investigated.

The only digging activity that I found in the area did not occur near the Biss Brook. Also, at the farm the brook was almost completely fenced off from cattle, due to the farm history, although there were a couple of gaps in the southern fields where cattle could potentially have had access to the brook to drink. When I inspected the premises, some soil erosion could be seen in a spillway ditch near the old burial sites in the southern fields. I also had to consider that the first animal could have been dead for several days and, although at the time of reporting disease they had moved, the rest of the cattle group could have had access to contaminated material before the farmer reported suspicion of the disease.

After due consideration, the true source of the disease could not be found, but the premises were believed to be contaminated, especially those fields next to the brook. These concerns were the basis of the risk assessments produced before lifting the restrictions and applying conditions on the premises at the end of the incident.

As part of the risk assessments and epidemiology of the incident, the possible spread of the disease was considered, including all movements of cattle back to the main farm since the first case occurred, and the silage produced from the fields in Westbury and stored at the main farm. After the statutory period of 21 days after the last confirmed case, restrictions were lifted on 16 November 2015. In consultation with Defra, special conditions were applied in the form of statutory notices. The aim of these notices was to mitigate the risk of further exposure to anthrax infection in subsequent years, so it was decided to impose the following conditions: only vaccinated ruminants were to be allowed to graze the premises for three years. Additionally, all silage produced from the premises must be fed only to vaccinated ruminants for three years and no arable crops were to be sown in the fields next to the brook for three years. It was also advised to restrict access to the erosions on the drainage ditch.

Challenges

From early on, it was evident that I would face challenges, as anthrax cases are rare in Great Britain.

Some of the problems included:

  • Gaining access to old files.
  • Communicating with experts.
  • Communicating with officers who had dealt with previous incidents.
  • Getting information about anthrax vaccination, as the product is no longer licensed in the UK.
  • Not knowing how effective a vaccination programme might prove to be.
  • Licensing procedures (from ashes to animals, to the import licence for the vaccine).

It wasn’t until later into the investigation that I managed to discuss findings with experts and deliberate potential vaccination. I also aided the farmer and private vet in acquiring the vaccine from a laboratory abroad, which was time consuming and costly to the farmer.

Lessons learned

As always there are lessons to be learned, one of which was to ensure suitable precautions were taken when dealing with any report case, due to the potential risk to health if confirmed.

As a result there was an extensive internal review of health and safety, biosecurity on site and procedures.

Another lesson learnt was the need to create a network of experts in the field, who could be approached in crisis situations, when advice might be required on any aspect of the disease.

If you are involved in investigating anthrax, please be sure to take appropriate precautions, and please don’t assume that because the disease is rare it will definitely be ruled out.