Trouble in Transylvania
Wild boars are attracting increasing attention because of the organisms they carry, many being transmissible to humans who come into contact with them
For many of us, Transylvania is best known as the homeland of Bram Stoker’s famous character, the vampire Count Dracula, who lived in a remote castle in the Carpathian Mountains. The Irish author’s Gothic horror novel appeared in 1897, but it was not until 1914, two years after Stoker died, that the short story Dracula’s Guest appeared in print. A deleted chapter from the original manuscript, it was this that gave the volume its name.
Now, a century later, there is a microbiological reason to be aware of Transylvania too. For it is there, in a region that today forms the central part of Romania, that a danger to human health has become apparent with the detection of Anaplasia phagocytophilum in wild boars (swine). As well as being the agent of tick-borne fever in ruminants, equine and canine granulocytic anaplasmosis, this obligate intracellular pathogen causes the emerging human disease granulocytic anaplasmosis. One of the major wild ungulate game species in Transylvania, the wild boar (Sus scrofa) is increasingly managed for hunting. The new fınding, by Timea Kiss and others at the University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca, Romania, arose from their concern about the relatively high numbers of wild boars and their frequent overlap with human activities in the region. Oddly, however, there have been no previous large-scale studies of the prevalence of A. phagocytophilum in boars. The omission is even more surprising given that three years ago the organism was identifıed in Ixodes ricinus ticks, while serology confırmed exposure in horses and dogs.
Timea Kiss and colleagues sought to understand what was happening “in the fıeld” by obtaining 870 samples from the spleen, kidney, and liver of wild boars in 16 Romanian counties over two periods of two years each. They then identifıed A. phagocytophilum DNA using a nested PCR protocol that amplifıed a fragment of the 16S rRNA gene.
As reported in Epidemiology and Infection (142: 246, 2014), the group found a global prevalence of 4.48% in wild swine for the entire study period, the fıgure rising from 2.29% during the fırst two years to 6.67% during the second period (when the organism was detected in two additional counties). Positive cases tended to concentrate in the central region of the country. “Our results confırm that Transylvanian wild boar is naturally infected with A. phagocytophilum, raising awareness concerning a potential zoonotic cycle,” the authors write. “By gaining a fırst glimpse into the molecular epidemiology of A. phagocytophilum in Transylvania, it becomes obvious that concerted efforts of veterinarians and medical practitioners will be necessary to assess the risk represented by this pathogen in Romania.”
The Cluj-Napoca team cites recent studies showing that sequencing of the groESL gene has confırmed that genetic variants of A. phagocytophilum isolated from wild boars in Slovenia, Poland, and the Czech Republic were identical to those implicated in human granulocytic anaplasmosis. This suggests that these animals play an important role in the transmission cycle of this pathogen.
Taken together, all these data demonstrate that the role of wild swine as sources of A. phagocytophilum is far from fully elucidated at the moment. “Even if their reservoir capacity remains debatable, because of their relatively high numbers, ease of access to tissue samples, and presumably rapid clearance of the pathogen, wild boar would represent a good choice as sentinels, providing a sensitive environmental risk indicator of changes in the epidemiology of A. phagocytophilum,” the authors write. “This would be especially true for strains known to be pathogenic for humans, but their utility as such remains to be evaluated.”
The investigation in Romania has come at a time of growing concern over possible health hazards associated with wild swine, which are indigenous in many countries and which can harbour viruses, bacteria and parasites communicable to humans and their companion animals. “Changes in human habitation to suburban areas, greater use of land for agricultural purposes, increased hunting activities, and consumption of wild boar meat have raised the chances of exposure of wild boars to domestic animals and humans,” write one group of researchers at Virginia Polytechnic Institute and State University, Blacksburg, Va., in the Philosophical Transactions of the Royal Society B (364: 2697, 2009). “Wild boars can act as reservoirs for many important infectious diseases in domestic animals, such as classical swine fever, brucellosis and trichinellosis, and in humans diseases such as hepatitis E, tuberculosis, leptospirosis and trichinellosis.”
The incidence of tuberculosis in wild boars has risen in recent years, posing a potential problem in both humans and livestock, while a trichinellosis outbreak has been linked with the eating of feral boar meat in Canada. Another incident occurred in Florida, where hunters contracted Brucella suis from wild swine. As recorded in MMWR (56:53, 2009), the Centers for Disease Control and Prevention were contacted in 2008 by the state departments of Pennsylvania and South Carolina regarding brucellosis possibly linked with swine hunting. Investigation confırmed that two patients defınitely had B. suis infection, and that the brother of one of them probably had the disease. All three exposures were associated with hunting, but two of the patients did not show symptoms until 4–6 months after exposure. The report concluded that clinicians treating individuals with an unexplained febrile illness should consider brucellosis and obtain a thorough history not only of food intake and travel to enzootic areas but also of occupation and recreational activities, including swine hunting.
An especially interesting feature of the Florida scenario was that one of the patients, who had received a total left knee arthroplasty four years previously, was referred to a local hospital emergency department after a week of fever, malaise, headaches and a swollen left knee. Initial investigations indicated a Corynebacterium urealyticum infection and the patient received appropriate antibiotics. However, it then emerged that B. suis was the real culprit. Given levofloxacin and daptomycin, the man recovered after six weeks with no permanent knee damage.
Further enquiries revealed that the patient had not only hunted feral swine in southwestern and south central Florida but had also helped to fıeld dress and butcher eight or nine swine at the two locations. He had not worn any protective equipment, but had cut his hand while dressing one of the animals. He then stored the meat in a freezer at home and ate it over several months. No other risk factors for brucellosis were identifıed.
Another concern regarding wild boars is highlighted by the Blacksburg, Va., group. They point out that these animals also pose a serious problem for countries that are trying to eradicate zoonotic diseases such as brucellosis, hepatitis E, tuberculosis, and trichinellosis in humans, but also pseudorabies, porcine-associated circovirus-associated infections, and other conditions in livestock. “This is especially relevant,” they write, “for disease-free populations of animals and humans not exposed previously to the agents from wild boars and with no herd or population immunity, and thus highly susceptible to such infectious agents.”
I began in dramatic mode with Dracula, and while one should not overdramatize the potential dangers to human health from microorganisms in wild boars, the threats are clearly apparent from the remarkable number of papers on this subject appearing in the Journal of Wildlife Diseases over the past fıve years. One of the most recent, by Yuka Hara and coworkers, published on line in February this year, described the high prevalence of hepatitis E virus in feral pigs in Yamaguchi Prefecture, Japan.
Watch this space.