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Veterinary surgeons and zoonotic diseases

The need to know more about transmission from animals to humans and the whole area of what to do about it is set for an explosion of awareness

Forty years ago, zoonotic flu was a hot topic for discussion for veterinary surgeons, farmers and rural doctors (Bell et al., 1988; Gard, 1991; Stanford and Hall, 1991). Little noise was generated for the next 39 years and then along came the COVID-19 pandemic. Logically, veterinary surgeons were propelled into the front line for defence and understanding with enquiries building up from many directions, not least students from a range of study areas.

The need to know more about transmission from animals to humans and the whole area of what to do about it is set for an explosion of awareness. Be prepared for colleagues, who have laboured for years with little consideration, being dusted off and pushed into the technical limelight. The fundamental understanding appears to be that provided disease stays within animals, the nation isn’t particularly alarmed and if a few individuals are ill then so be it, but if the disease passes from human to human, with deaths, then tin hats will be issued.

Much is being highlighted about “long COVID” and the time taken to recover fully from disease. It is too early to know whether there may be a recurrence of flu-type illness in later life. Many veterinary surgeons will be aware of the long-term consequences from brucellosis where colleagues took the prudent course of leaving clinical practice and moving into industry or government service. Anyone who has travelled with a brucellosis vet – on a hot summer’s day, when they are wearing a hat, overcoat and gloves with the car heater at full blast and they are still shivering, a decade after attending their last case of abortion – will have an inkling of the life-changing consequences of zoo flu. The clinical features are listed as undulating fever, malaise, weakness, fatigue, rigors, night sweats, headache, backache, joint pains, weight loss and other systemic symptoms, including depression, that may persist for months or years with frequent recurrences (Bell et al., 1988). That is probably a good summary of the likely effect of zoonotic infections on humans.

Diagnosis can be a great difficulty. After a period of hot weather, in the summer, there was a deluge of rain in Dublin. The organisers of a multi-activity sports event were delighted because the competitors could now swim the river Liffey as planned, unaware of the accumulated contents of the drainage flowing into the water. The competitors returned home to various parts of Europe and a few suffered zoo flu symptoms, ranging from headaches to systemic failure and admission to intensive care. If the athletes had been sewage workers, then leptospirosis infection might have been immediately recognised, whereas delays in diagnosis and suspicion of performance-enhancing drug use had consequences. The link between rats, urine, abrasions and people was not obvious. A few veterinary surgeons have experienced a similar problem with L. hardjo. Fortunately, their occupation allowed worthwhile enquiries, but the link between infected cows and their urine is not obvious to anyone who has not witnessed milking, with cows urinating onto the floor in a herringbone parlour.

The medical responses to zoonotic infection can also lead to over-enthusiasm. Anyone associated with open farms will be aware of the risk from orf virus. Children cuddle the lambs and may return home with contagious pustular dermatitis. The real clinical danger is from secondary bacterial infection and the virus is self-limiting. However, with orf and also ringworm, surgery is said to have been carried out, which if the infection is on the face may lead to unsightly scarring for life. The veterinary role in advising management to control the virus may become very important for some youngsters. This alert role has been shown to be important with Rickettsia, and dry dung blowing in the wind has been reported as the source of acute Q fever with potential long-term consequences (Wilson, 1991); an influenza-type illness with headache, joint and muscle pains from inhalation of aerosols of infected dust is associated with Chlamydia, and poultry processors and vets are said to be at risk (Bell et al., 1988).

Much has been written about the dead crows at the Bronx zoo and the human cases of West Nile virus that have developed in the USA over the past two decades. It is interesting to follow the sequence from an infected imported bird being bitten by a mosquito that feeds on other birds and animals, and also bites humans, where the extended breeding season with weather changes provides greater scope for virus transfer. However, the significant understanding is how difficult it was for the vets at the zoo to get confirmation of the link between crow death, other birds and animals, and human risk. Move up to coronavirus from bats to pangolins, to wildlife markets, to human-to-human transfer and the base activity is veterinary with the recognition of animal disease. It may become clear whether the animal to human risk with coronavirus was recognised but not acted upon before the pandemic. In future, it seems likely that zoonotic animal disease will be studied and resources applied with the deserved intensity.

Although unpasteurised milk is not usually implicated in current cases of tuberculosis in the UK, the disease is an example of an animal disease passing to people and then within the human population. The textbook prognosis is a slow, progressive disease leading to emaciation and death if untreated with the indication that recurrences of infection may occur in later life (Bell et al., 1988). It is the possible longer consequences that raise one disease from being a short-term trouble to a lifelong threat.

The ongoing work to identify disease threats on the horizon is to be applauded. Surveillance in the UK and overseas can expect to move up the funding agenda. Outbreaks show vets and others in full protection suits and the risk to people is presumably real. We will all need to pay attention to the health surveys of people that have been in contact with dead and dying birds and particularly whether transfer occurs from human to human. It is interesting that many of the disease assessments include washing of hands as a primary precaution against disease. With all the attention given to personal protection from COVID, the whole role of PPE is expected to feature in future papers and presentations. It is hoped that we will all pay detailed attention to infection transfer now. “Hands, face, space” is expected to be a permanent mantra. A database of annual vet and animal keeper occupational illness would act as a guide to real risks.