3rd CVBD Symposium
April 16-19, 2008, Wiesbaden, Germany
“Using repellents remains the best prophylactic measure for dogs against the increasing global threat of parasite-transmitted infectious diseases.” This statement from Dr. Jean-Pierre Dedet, University of Montpellier, France, summarizes the discussions of 36 experts in natural sciences, veterinary and human medicine from Europe, North America and Asia during the 3rd International CVBD (companion vector-borne diseases) Symposium in Wiesbaden, Germany. The members of the CVBD World Forum spent two days discussing current scientific data and future developments. They agreed that current guidelines for registration of ectoparasiticides in the veterinary field, however, do not fully reflect the common knowledge about threats posed by disease-transmitting arthropod vectors.
Being a major zoonotic disease endemic in more than 70 countries in the world (recently even found in the US), canine leishmaniosis was the predominant topic in this year’s symposium on CVBD. According to seroprevalence studies from Italy, Spain, France and Portugal, about 2.5 million dogs in these countries are infected. However, many of these dogs do not present any clinical signs. Dr. Gad Baneth from the Hebrew University, Rehovot, Israel: “This makes canine leishmaniosis a diagnostic challenge for the veterinary practitioner, clinical pathologist and public health official in endemic countries as well as in non-endemic regions where imported infection is a concern.”
Has canine leishmaniosis, a disease of warmer regions like the Mediterranean area, become endemic in Germany lately? Dr. Torsten Naucke from the German organization “Parasitus Ex”, Niederkassel, reported on eleven cases of autochthonous (human/canine/feline/equine) leishmaniosis in Germany since 1991. As a putative vector, sand flies of the species Phlebotomus mascittii have been identified. In summer 2007, the northernmost finding of this species ever happened along the river Moselle near Cochem. And in February 2008, winter activity of adult P. mascittii in Europe could be proved for the very first time on the island of Corsica. For Dr. Naucke, these are two indicators for an increasing distribution of putative disease-transmitting parasites and their prolonged seasonal activity.
According to Dr. Jean-Pierre Dedet, University of Montpellier, France, increasing risk factors are making sand fly-borne diseases such as leishmaniosis the major public and veterinary health problems in numerous countries. In the absence of efficient vector and/or pathogen control programs, he recommends to avoid host infection and subsequent disease as a means of prevention. Therefore, humans should be prevented from intruding into natural zoonotic foci and protected against infective bites of sand flies. For dog protection, he recommends the use of permethrin-based ectoparasiticide spot-ons. Deeper insights into the dependence of vector and pathogen transmission on environmental factors like landscape, housing and infrastructure were provided by epidemiologist Dr. Marc L. Wilson, University of Michigan, USA.
Although canine leishmaniosis is usually transmitted through bites of infected sand flies, Leishmania pathogens may also be transmitted from dog to dog via the placenta, sexual contact, other vectors or blood transfusion, explained Dr. Xavier Roura from the Universitat Autònoma de Barcelona, Spain. Screening blood from an animal blood bank which obtained blood from donors living in an endemic area, he recently found Leishmania DNA in 19.6% of the samples analyzed. With PCR testing of seronegative dogs and with the use of leukoreduction filters, the potential risk of Leishmania transmission might be reduced.
In national surveys (1987 and 2004) based on information from veterinary clinics, Dr. Patrick Bourdeau from the Ecole Nationale Vétérinaire de Nantes, France, saw an expansion of leishmaniosis in his country. In 2004, new areas (departments) were found to be infected, especially in the southwest of the country. The number of enzootic departments where clinics have seen more than 50 cases per year increased from 6 areas in 1986 to 12 in 2004. From the latest study, Dr. Bourdeau concludes a national overall prevalence of canine leishmaniosis in France from 1.3 to 9.6 cases per thousand. Apart from leishmaniosis, several tick-borne diseases were surveyed nationwide. Interestingly, nearly 90% of participating veterinarians claimed themselves to be poorly informed about tick-borne anaplasmosis.
Dr. Barbara Kohn from the Free University of Berlin, Germany, sees anaplasmosis as another “emerging disease” in animals since its vector populations seem to increase continuously. In Europe, seroprevalence for Anaplasma phagocytophilum in dogs ranges from 7.5% (Switzerland; for the former Ehrlichia phagocytophila) over 22% (Sweden; for granulocytic Ehrlichia spp.) to 56.5% (Austria). For Germany, 43-50% seroprevalence (dependent on the region) were found using an immunofluorescence antibody test (IFAT). Regarding clinical signs, the most consistent findings were fever, lethargy or depression, and anorexia, occurring in over 75% of dogs.
Looking closer to Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in German dogs with an ELISA detection system, Dr. Reinhard Straubinger from the University of Leipzig, Germany, found a nationwide average detection rate for A. phagocytophilum of 21.5% - with very high levels in southern parts of the country. Dr. Straubinger: “The fact that almost every fifth dog carries antibodies against this agent should most importantly prompt veterinarians to consider this infection during their routine diagnosis.” Analyzing samples from a randomly selected population of dogs, seroprevalence for B. burgdorferi was 7.7%. Both seroprevalences seem not to correspond with the respective infection rates of ticks found in Germany. Dr. Straubinger: “One reason might be that the intracellular parasite A. phagocytophilum manages to hide from the immune system much quicker and more efficient than Borrelia burgdorferi. It retreats into the intracellular environment, while at the same time non-protective antibodies are induced.”
Next to Lyme disease, tick-borne encephalitis (TBE) is the best known tick-borne human infection in central and eastern Europe. According to Dr. Gerhard Dobler from the Bundeswehr Institute of Microbiology in Munich, Germany, the virus is responsible for more than 10,000 human cases of CNS infections annually, among them more than a hundred fatal cases. A large variety of rodents, larger mammals and birds can be infected after tick infestation. Clinical manifestation in dogs resembling the symptoms of human meningoencephalitis has been described. Given the high antibody prevalence rates in dogs (up to 30%) it is likely that overt disease in dogs is a rare clinical outcome of TBE virus infection.
In North-Eastern Italy, Dr. Gioia Capelli from the Istituto Zooprofilattico Sperimentale delle Venezie, Italy, tried to fill the informational gap on ticks and tick-borne diseases by collecting and analyzing ticks of the species Ixodes ricinus, the vector of anaplasmosis, Lyme borreliosis, and tick-borne encephalitis. Her main purpose was to assess, predict and prevent the risk of human infection. Preliminary results show a huge variety of tick population density and infection rates which highlights the need of assessing the risk of tick-borne diseases on a local basis.
The emergence of new arthropod-borne pathogens has been another main topic during the two days in Wiesbaden. Dr. Ricardo G. Maggi from the North Carolina State University, USA, talked about Bartonella bacteria, which are increasingly recognized as important pathogens in veterinary and human medicine. They are transmitted by arthropod vectors (depending on the Bartonella species, e.g. fleas, lice, sand flies and ticks) or by animal scratches or bites. With a unique approach using blood pre-enrichment and PCR, Dr. Maggi identified four different Bartonella species in the saliva of dogs. Dr. Maggi. “This finding is in conjunction with previous case reports of sporadic Bartonella transmission by dogs. It suggests that Bartonella infection may represent an occupational risk for veterinary professionals and others with extensive animal contact.” Pathogenesis in humans after a Bartonella spp. infection was further elucidated by Dr. Volkhard Kempf from the University Hospital in Tuebingen, Germany. He stressed “the unique ability of these pathogens to cause vasculoproliferative disorders as well as intraerythrocytic bacteraemia”.
Rickettsia species are another growing group of bacteria transmitted to humans and animals by bloodsucking arthropods. Dr. Martin Pfeffer, Bundeswehr Institute of Microbiology in Munich, Germany: „There is barely a month in which no new Rickettsia species, subspecies or genotype is described. Most of these are found in ticks, but whether they are pathogenic for man and animals remains speculative in most cases.” Tick-transmitted Rickettsia infections are an emerging problem in dogs. In addition to causing serious disease in traditional tropical and semi-tropical regions, they are now increasingly recognized as a cause of disease in dogs in temperate climates and urban environments.
Dr. SungShik Shin, Chonnam National University Gwangju, South Korea, presented the situation of vector-borne diseases of dogs in his country. He sees heartworm disease, caused by Dirofilaria immitis, “by far the most important and wide-spread internal disease of dogs in Korea”. Dogs and humans in South Korea are also infected by Thelazia callipaeda, the oriental eyeworm, which causes ocular lacrimation. Apart from these infectious nematodes, ubiquitary tick-transmitted pathogens like Anaplasma phagocytophilum, A. platys, Ehrlichia chaffeensis, E. canis or Rickettsia rickettsii have been found in both ticks and small rodents using DNA amplification in South Korea.
More detailed information about the eyeworm Thelazia callipaeda was added by Dr. Domenico Otranto from the University of Bari, Italy. Mostly, T. callipaeda is found in the conjunctival sac or lachrymal apparatus of dogs, but occasionally also in humans. Vectors of this nematode are fruit flies. Feeding on animal lachrymal secretions, these insects become infected with first stage larvae, as Dr. Otranto explained. After third stage male larvae have developed, the nematodes emerge from the infected fly as soon as these feed on the lachrymal secretions of receptive animals. In Europe, Italy is known for being endemic regarding the oriental eyeworm, with local prevalences of up to 60%. More recently, autochthonous cases of thelaziosis in dogs and cats have been described in south-western France and in Switzerland.
For Dr. Norbert Mencke, Director of Global Veterinary Services at Bayer Animal Health GmbH, it was “fascinating to see how veterinary and human medicine move together when talking about companion vector-borne diseases. The role of the dog as a reservoir for some human diseases and as a potential sentinel in others is far from clear, but worth studying intensively. When it comes to diagnostics or epidemiology, research in both fields can generate a lot of synergies.”