How fast is Lyme disease spreading?

Lyme disease cases in Europe

In Europe, there have been 360,000 reported cases of Lyme disease over the last 20 years (Source: World Health Organisation).

Lyme disease is the commonest vector-borne disease in Europe (Source: World Health Organisation).

 

Lyme disease cases in the UK

In England and Wales, an estimated 3,000 people are diagnosed with Lyme disease each year. In other words, 8 people are infected every day. (Source: Public Health England)

This figure of 3,000 cases per year (estimated by Public Health England) is around 3 times the number of cases that the National Reference Laboratories in England (called RIPL) and Scotland (called the NLBTL) diagnose by blood test. The estimate is based on the belief that about two-thirds of Lyme patients have an erythema migrans rash, and can therefore be diagnosed visually by their doctor without needing a blood test; the number of patients diagnosed this way is not recorded centrally, so nobody knows confirmed figures.

How rapidly is Lyme disease really spreading?

In England and Wales, confirmed cases of Lyme disease almost quadrupled in the ten year period between 2001 and 2011, when there were approximately 1,000 new cases reported. (Source: NHS choices)

NHS Choices website reports:

“The ongoing rise in Lyme disease cases in the UK – thought to be driven by climate change, leading to warmer winters – has been known by public health officials for some time. Reported cases in England and Wales rose from 268 in 2001 to 959 in 2011, but the true figure is thought be much higher. Current estimates put the actual figure at around 3,000 cases a year in England and Wales.”

In Europe, aggregated national figures for the whole region are published by the World Health Organisation and the European Centre for Disease Control. Published on the CISID website, they record that newly diagnosed cases of Lyme disease were around 2,400 in 1990 and had risen to 35,000 by 2010.

Download: WHO / ECDC Information sheet on Lyme disease

Link: WHO/ECDC/CISID website

Over this 20-year time period, new cases of Lyme disease in Europe increased by about 1,300%, which equates to an annual average growth of 65% each year relative to the number of patients in 1990. In reality, as the graph shows, the increase was more than this in some years and less in others.

The compound annual growth rate over this time period, showing the year-on-year growth, was 14%. This figure is the median year-on-year increase over the two decade time period, but in reality growth accelerated at a higher rate than this between 1997 and 2006, and then levelled off between 2006 and 2010. Frustratingly, the WHO/ECDC has not published more recent aggregated figures.

We do know, however, that reporting standards and methods of gathering data vary from each European country to the next, and also over time. In the UK, for example, official figures only report on the minority of patients diagnosed by blood test, whilst the majority, who are diagnosed by EM rash, are excluded from the reported data. Similar anomalies exist across the continent and result in significant under-reporting.

A research paper aiming to adjust the figures and arrive at a more representative estimate was published by The Journal of Public Health in 2016, and concluded:

“LB (Lyme Borreliosis) is a continually emerging disease and the most common zoonotic infection in Western Europe approaching endemic proportions in many European countries.”

Download: An estimate of Lyme borreliosis incidence in Western Europe, Robert A Sykes

Link to Source: Journal of Public Health

How does this compare with other diseases?

Lyme disease is the most common of the vector-borne diseases in Europe. Vector-borne disease are infections spread by biting insects, arachnids and other parasitic animals.

Lyme disease is the fastest spreading vector-borne disease in Europe. (Source: World Health Organisation)

“Vector-borne diseases account for 17% of the estimated global burden of all infectious diseases.” (Source: World Health Organisation)

Zsuzsanna Jakab, WHO Regional Director for Europe said at a WHO conference in 2014:

“There is a clear warning signal to the European Region that diseases carried by vectors may spread and intensify in the years ahead. This is not the time to lower our guard.”

Whilst the incidence of Malaria is now falling sharply in Europe, Lyme disease is persistently increasing. As this graph produced by the WHO shows, Lyme disease is spreading far faster than other vector-borne illnesses in Europe:

Key: Vector-borne diseases in this graph are Lyme disease (ticks), Malaria (mosquitoes), West Nile Fever (WNF) (mosquitoes), Tick-Borne Encephalitis (TBE) (ticks), Crimean-Congo Haemorrhagic Fever (ticks) and Leishmaniasis (sandflies).

Source: Download PDF presentation World Health Day 2014 VECTOR BORNE DISEASES (EUROPE)

Lyme disease is also spreading faster than some other worrying diseases in Europe. This graph shows the increase in new cases of HIV-AIDS, Measles and Lyme disease throughout Europe from 1991 to 2010 (Source: CISID – World Health Organisation)

Why is Lyme disease spreading so fast?

One of the contributing factors to increases in Lyme disease incidence would be changes in the weather, and thus in the tick population, and in the numbers of people spending time outside, and in how much clothing they were wearing to protect their skin.

The sheep tick (Ixodes Ricinus) is the most common tick in the UK. One theory is that, due to climate change and warmer weather, tick reproductive activity appears to be increasing, and in particular benefitting from earlier, warmer springtime weather. Ticks climb up long grass and other plants and attach to passing mammals; clearly humans with bare legs are more vulnerable than those in long trousers.

Another theory is that humans are simply building on more and more greenfield sites, which have traditionally been tick habitats, and are therefore coming into more frequent contact with the arachnids.

Another driving factor could be the presence of pets. The University of Bristol, UK, has an ongoing research project called the Big Tick Project which asked veterinarians across the UK to conduct spot check on dogs and cats brought into their consulting rooms and report the numbers of ticks they find. They found that 1 out of 3 dogs in the UK has a tick feeding from it in spot checks. (Source: The Big Tick Project)

It is easy to see how ticks which attach unnoticed to dogs walking in the countryside may then detach when the same dogs are taken to an urban park, or even in their owner’s garden, and thus a tick population may begin to establish itself in a new spot. A recent research project found ticks carrying Lyme disease in Richmond Park and Bushy Park in London. (Source: Medical and Veterinary Entomology)

The de facto hosts of ticks are small, ground-dwelling mammals including mice, squirrels and also some birds. These animals spread widely and also come into close proximity with human dwellings and recreation areas.

So far, no systematic research has been done to establish facts. One research paper, reported finding that 6% of ticks in a region of the UK it researched were carrying Borrelia Burgdorferi. Another paper, in another region, found 25%. These are really nothing more than “spot checks” but we do know that levels vary greatly by region and, indeed, from one year to another.

Most cases contracted within the UK

PHE patient records suggest that 15% of UK Lyme disease patients contract the disease abroad, whilst 85% of them catch it within the UK.

Many cases probably missed

A patient survey conducted online in 2011 by Lyme Research UK highlighted some of the problems with the way in which the NHS handles Lyme disease, with over a third of patients claiming that the delay in being accurately diagnosed was due to initial misdiagnosis. Only 31% patients were diagnosed by a GP and over 70% patients had to wait 6 months to obtain a diagnosis. Furthermore, 65% of patients considered the NHS care they received to be ‘inadequate.’

Adam Hughes Photography-1950

Sources

All sources are provided in hyperlinks and downloadable documents throughout this article.

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