A viral hurricane?

The UK chief medical officer Liam Donaldson recently announced that checks would be stepped up on West Nile Virus (1). Studies show that there are now birds in the UK infected with the virus, but there have not been any human cases of the disease. Is Donaldson taking a sensible precaution, or overreacting?

West Nile Virus is found mainly in birds, though it is also found in horses and other mammals. It is spread to humans by mosquitoes that have previously bitten an infected animal, but cannot be spread from person to person. Even in affected areas, only about one percent of mosquitoes carry the virus (2).

It is generally harmless to humans, with 80 percent of those infected suffering no ill-effects at all. In 20 percent of cases, mild flu-like symptoms are experienced. However, in about one in 150 cases, serious illness results, including high fever, convulsions and paralysis. Of these serious cases, about 12 percent die. Death rates are highest among the elderly (3).

West Nile Virus was first isolated in 1937 in Uganda. It has spread in recent years to temperate regions, with the first cases reported in the USA in 1999. Between 1999 and 2001 there were 149 cases in the USA, leading to 18 deaths. In 2002 there was a sharp increase, to 4156 reported cases and 284 deaths. So far in 2003, there have been 536 cases with 11 deaths (4).

Statistics released by the US Centers for Disease Control and Prevention (CDC) in Atlanta in early August showed that the case count for 2003 had trebled in one week. The bulk of cases in 2003 have been in Colorado, which was largely untouched in the previous year. These statistics were widely – and often worriedly – covered. The state epidemiologist in Louisiana, an area that was badly hit in 2002, described West Nile as ‘a viral hurricane’ (5).

Yet the case count hardly justifies the amount of attention the disease attracts. The US population is about 290million people. So the 284 deaths in 2002 really were one-in-a-million. Or to put it another way, West Nile Virus was responsible for about 0.01 percent of the 2.4million deaths in the USA in 2002. By comparison, influenza kills over 2000 people per year (6).

The small size of the risk hasn’t stopped the public health campaigns. ‘Fight the Bite’ is the CDC’s response to West Nile Virus, which aims is to prevent people from getting bitten by mosquitoes (7). This, of course, is a perfectly reasonable aim – but given the rarity of the disease, it surely would be more sensible to avoid mosquitoes for more mundane reasons. Being dinner for a swarm of insects is nobody’s idea of a good time.

The danger is that all the discussion about the virus might dissuade people from enjoying the great outdoors during the summer – which is just the kind of activity once regarded as healthy and wholesome.

The amount of coverage given to West Nile Virus seems strange at a time when infectious disease is less important. For example, in the CDC’s provisional statistics for deaths for the year 2000, no infectious disease rates higher than seventh among causes of death, and even this is an amalgamation of the figures for influenza and pneumonia (8).

This makes Liam Donaldson’s report, ‘Health Check: On the state of the public health’, seem all the more strange. In a 68-page report which is supposed to be an overview of the major health issues that face Britain, West Nile Virus occupies 10 pages. Not only have there been no cases of West Nile Virus in the UK, but the chances of there being any are rated low, even in the report.

Just how low is suggested by the press release for Liam Donaldson’s report: ‘…if a number of factors conspired, namely bird migration, the size of the mosquito population and change in climatic conditions, then it is not impossible that West Nile Virus could arrive in this country.’(9) It seems that Donaldson is more concerned to appeal to fears of unlikely infection than to deal with real health problems.

What this demonstrates is that the concern with West Nile Virus is less a response to a real threat posed by the disease to people in the West, than it is a consequence of a general tendency to exaggerate the threat of disease to society. Remember the SARS panic, earlier in 2003? SARS was identified as a new threat in February, and at one point there was gloomy talk of SARS causing millions of deaths. Yet there hasn’t been a new case reported since 15 June. The panic around SARS, however, caused far more harm than the disease itself (see WHO’s to blame for the SARS panic?, by Rob Lyons).

The irony is that the CDC was set up in 1946 in a building formerly occupied by the Office of Malaria Control in War Areas, at a time when malaria was still prevalent in the southern USA (10). While malaria still kills millions in Africa, it seems perverse that another, much rarer, mosquito-borne disease is occupying so much of the energies of medical authorities in USA and the UK.

(1) Annual Report of the Chief Medical Officer 2002, UK Department of Health

(2) What you should know about West Nile virus, American Veterinary Medical Association

(3) West Nile Virus: What You Need To Know, Centers for Disease Control and Prevention

(4) West Nile Virus: 2003 Human Cases as of August 18, 2003, Centers for Disease Control and Prevention

(5) West Nile Virus set for fresh rampage across US, New Scientist, 8 August 2003

(6) Deaths: Preliminary Data for 2000. Vo. 49, No. 12. October 9, 2001, Centers for Disease Control and Prevention

(7) Fight the Bite!, Centers for Disease Control and Prevention
(8) Deaths: Preliminary Data for 2000. Vo. 49, No. 12. October 9, 2001, Centers for Disease Control and Prevention

(9) Press release: reference 2003/0252, UK Department of Health, 3 July 2003

(10) CDC Historical Highlights, Centers for Disease Control and Prevention