Q fever: The Dutch experience
The August 2008 Zoonotic Infections column, titled “Q fever: a reemerging zoonosis,” examined a Q fever epidemic of unusual magnitude in the Dutch province of Noord-Brabant.
Between the end of 2007 and July 2008, 491 cases of Q fever were registered; estimates by the province’s public health authorities indicated that about 5,000 people had been infected. It was assumed that the main source of infection was aborted dairy goats and sheep.
It was also believed that the disease was affecting people who had no contact with animals, who were likely infected by airborne Coxiella burnetii. The disease in animals was then declared notifiable. Control measures included restrictions upon animal movements and upon the transportation and use of manure from all goat and sheep farms in the affected zone. Pasteurization of milk from affected farms, before its use for home-made dairy products, became compulsory. Vaccination of the animals with a commercially available, inactivated vaccine was considered.
The epidemic continues
During the rest of 2008, more than 500 additional cases were diagnosed in the southern part of the Netherlands, and animal vaccination was started. However, the disease reappeared in the spring of 2009. By the end of 2009, more than 2,200 additional human cases have been diagnosed. The epidemic is now the largest ever on record in the world. At the end of 2009, additional control measures had to be undertaken by the Dutch government; the situation had become politically laden.
To try to reduce the number of human cases in 2010, Dutch officials decided to kill all pregnant goats on farms found infected. This will lead to the destruction of at least 40,000 goats, including uninfected animals.
At the end of December, the Netherlands officially notified the World Organization for Animal Health about the Q fever outbreak in 61 goat farms, the epizootic reportedly caused by a “new strain” of C. burnetii. The characteristics of the strain are still to be published at the time of this writing.
The following information has been collected from recent official Dutch publications on the situation, in particular concerning the research efforts invested in the animal health and public health domains.
The dairy goat population in the Netherlands, particularly in Noord Brabant, has increased almost 10-fold during the last decade; some flocks now include thousands of animals. This is regarded as unique and may be the background to the event.
Since the early stages of the Q fever epidemic in Noord-Brabant, it seemed that there was a link between the concentrated goat population in the area, the appearance of Q fever abortion storms within the goat farms and the Q fever cases in humans. However, causal link had yet to be demonstrated. For this end, researchers collected data of human patients, infected farms and the topography of the infected area and climatic conditions to demonstrate possible connection. However, convincing evidence that the agent of Q fever in humans comes from goats can only be delivered if the genetic fingerprint of the bacterium in both cases is identical. Efforts have been invested in molecular studies of human- and animal-derived strains. Such investigations, preferably carried out in laboratory-cultured bacteria, require high-level biosafety conditions to protect the lab personnel. Such laboratory has been applied. So far, 11 subtypes of C. burnetii have been identified, one of which clearly appears at a higher frequency. There are clear similarities between human- and goat-derived subtypes, thus a causal link is likely. Final results are expected later in 2010.
To evaluate the extent of infection in small ruminants, a random survey was conducted in 2008. The results of this showed that almost 8% of the goats in the Netherlands were infected, fourfold the infection rate in sheep. The following step was the development of a PCR test for Bulk tank milk monitoring, covering the 450 dairy goat and sheep farms with more than 50 lactating animals each. The test is used to detect excretion of C. burnetii in the farm. Initial test is carried out by the regional animal-health service. If a test is found positive, a visit is paid to the farm, the issue explained to the owners and a second sample taken, sent for confirmation to the Central Veterinary Institute (in Lelystad). In case of confirmation, the farm is declared “infected.” The periodic bulk tank test has become initially compulsory on Oct. 1, 2009. On Dec. 14, 2009, it became a requirement to perform this test every two weeks instead of the previously requirement of every two months. The change is because excretion of the bacterium may be intermittent. It is not yet clear which factors contribute to the infection — or its absence — on goat farms within the infected zone; one research project is dedicated to this issue, results expected in 2011.
The airborne spread of C. burnetii in the vicinity of an infected source is long known. How far, and for what length of period, can the bacterium spread from an infected farm? This question is subject to another research project. For this end, the researchers prefer new infection foci in areas hitherto uninfected. When such a case is discovered, air is sampled at different distances from the new focus and at different times, tested for the presence of the bacteria. Initial findings show that the bacterium can be detected, shortly after the outbreak, at distances of 500 to 1,000 m around the infected farm. The duration of the bacteria’s detectability in the air is not yet known.
Vaccination of goats with an inactivated commercial, inactivated veterinary vaccine started at the end of 2008. The efficacy of the vaccine (decreased abortion rate, absence of bacterial excretion) and its safety under field conditions are under investigation; no results yet published.
The role that intensive farming plays in the Q fever problem in humans is a main subject for investigation. One possibility is the higher concentration of fine particles in the air on intensively managed farms. C. burnetii bacteria are known to attach themselves to dust particles, drifting with them to long distances. Results of this investigation are not yet available.
Although Q-fever remains subclinical, remaining undiagnosed or has very mild symptoms in about 80% of the cases, the disease may entail complications in individual cases. In pregnant women, for example, the disease is often chronic, with possible effect upon the unborn child. One of the studies addresses the possibility of premature birth, low birth weight or even death of the child. Other investigation groups perform studies into various treatment methods of patients with Q fever, into the impact of the disease upon the society as a whole, and upon its economical aspects in various settings. Others compare various treatment regimens and analyze the life span of patients. The possibility of Q fever transmission from blood donors in affected areas is subject to another investigation, of which the results are not yet available.
Another study deals with the occupational hazards and other risk factors. Obviously, farm-related activities increase risk of infection, particularly when including contacts with domestic animals, such as milking or litter handling. Various hygienic precautionary methods are evaluated for their risk reduction effect. The studies address the possible risks of outdoor activities, such as biking or hiking, and environmental conditions in rural or urban settings. The first results are expected from 2010 onward. Interestingly, less than 2% of patients with Q fever consumed raw milk products; hence, the consumption of such products is rather unlikely to have been a significant source of infection.
The results of the various research projects, and the outcome of the control efforts upon Q fever incidence in 2010, are anticipated with great interest in Europe and elsewhere.
Arnon Shimshony, DVM, is an Associate Professor at the Koret School of Veterinary Medicine Hebrew University of Jerusalem, Rehovot, and is the ProMED-mail Animal Diseases Zoonoses Moderator. Dr. Shimshony was Chief Veterinary Officer, State of Israel, from 1974 to 1999.