Fernando Simón

Human and Animal Dirofilariasis: the Emergence of a Zoonotic Mosaic

SUMMARY Dirofilariasis represents a zoonotic mosaic, which includes two main filarial species (Dirofilaria immitis and D. repens) that have adapted to canine, feline, and human hosts with distinct biological and clinical implications. At the same time, both D. immitis and D. repens are themselves hosts to symbiotic bacteria of the genus Wolbachia, the study of which has resulted in a profound shift in the understanding of filarial biology, the mechanisms of the pathologies that they produce in their hosts, and issues related to dirofilariasis treatment. Moreover, because dirofilariasis is a vector-borne transmitted disease, their distribution and infection rates have undergone significant modifications influenced by global climate change. Despite advances in our knowledge of D. immitis and D. repens and the pathologies that they inflict on different hosts, there are still many unknown aspects of dirofilariasis. This review is focused on human and animal dirofilariasis, including the basic morphology, biology, protein composition, and metabolism of Dirofilaria species; the climate and human behavioral factors that influence distribution dynamics; the disease pathology; the host-parasite relationship; the mechanisms involved in parasite survival; the immune response and pathogenesis; and the clinical management of human and animal infections.

Human Dirofilariasis in the European Union

The dog parasites Dirofilaria immitis and D. (Nochtiella) repens, well known as zoonotic agents, are widely distributed in southern Europe. Although both species are canine parasites, infection with immature worms has been found in humans, who develop nodules, mainly in subcutaneous tissue or in lung parenchyma arising from branches of the pulmonary artery. In humans, the parasites do not usually reach the adult stage and microfilaremia is absent, as has been shown by diagnosis using invasive methods for removing the nodules. In this article, Antonio Muro, Claudio Genchi, Miguel Cordero and Fernando Simón review the current situation concerning the clinical and epidemiological aspects, immune response and diagnosis of human dirofilariases.

What is new about animal and human dirofilariosis

Dirofilaria immitis and D. repens, the causal agents of cardiopulmonary and subcutaneous dirofilariosis, respectively, affect canine, feline and human populations with an increasing incidence in temperate and tropical areas of the world. In the past decade outstanding advances in the knowledge of dirofilariosis have been achieved. Nevertheless, questions such as the impact of climate change in the transmission and distribution of dirofilariosis, as well as a profound evaluation of both the role of Dirofilaria and Wolbachia and the proteins produced by them in the parasite-host relationship have not been fully addressed; therefore there must be milestones in dirofilariosis research in order to design new strategies and tools for the control of this disease.

Fasciola hepatica: vaccination of rabbits with native and recombinant antigens related to fatty acid binding proteins.

The current study was designed to compare the immunogenic and immunoprophylactic properties of native (nFh12) and recombinant (rFh15) antigens from Fasciola hepatica in rabbits infected with the fluke. Levels of specific anti-nFh12 and anti-rFh15 antibodies were significantly higher in the rabbits vaccinated twice compared with non-vaccinated infection controls. A reduction of 40% in worm burdens was found in rabbits immunized with nFh12 and infected 4 weeks after the second immunization. The recombinant vaccine induced lesser levels of protection than the native one, suggesting that both molecules may have slight differences either in immunogenicity or in their configuration. Further biochemical studies are required to define these differences. The mean length of flukes recovered was always smaller in all vaccinated rabbits. In addition, infected control rabbits had higher gamma glutamil transferase (GGT) levels than immunized rabbits. Lastly, gross anatomic observation always showed fewer liver lesions in all vaccinated rabbits than in controls. This finding clearly supports the possibility of vaccination regimes in fasciolosis.

Human Subcutaneous Dirofilariasis, Russia

We report 14 cases of human subcutaneous dirofilariasis caused by Dirofilaria repens, diagnosed from February 2003 through July 2004, in patients from Rostov-on-Don, Russia. Serologic analysis showed evidence of high risk of exposure to D. repens. Surveillance studies on prevalence and prevention effectiveness of canine infection are needed to control this emerging zoonosis.

Current prevalence of Dirofilaria immitis in dogs, cats and humans from the island of Gran Canaria, Spain.

The island of Gran Canaria is a hyperendemic area for canine dirofilariasis. The aim of the present study was to provide data on Dirofilaria immitis in dogs, cats, and humans on this island in 2010. The data confirms the prevalence in the overall canine population (19%), with a considerably higher prevalence (43%) in the autochthonous breed of Canarian Warren hound. The prevalence in the feline population (33%) is higher than that of the canine population, and the existence of specific D. immitis antibodies in the inhabitants of the island of Gran Canaria (12%) is confirmed. In both cats and humans, the prevalence, according to the different climate areas on the island, is related to the prevalence of D. immitis in dogs in the same area, which shows the key epidemiological role played by the canine host with regard to the transmission to other hosts of D. immitis.

Antibody and inflammatory responses in laying hens with experimental primary infections of Ascaridia galli.

Ascaridia galli, an intestinal nematode that affects hens and other domestic and wild birds, causes economic losses in avian exploitations. The present work shows that A. galli stimulates a strong antibody response as well as an intense inflammatory reaction, in the intestinal mucous of experimentally infected Lohmann Brown laying hens. IgG antibodies against soluble extracts of A. galli embrionated eggs and adult worms, were detected in both blood and yolks eggs from infected hens during a period of 105 days after the infection. This indicates that hens transfer to their offspring a part of the IgG antibodies produced when they become infected. The antigens responsible for the stimulation of specific IgG were molecules of 30-34, 44-54 and 58-90 kDa, while in the yolk eggs of infected hens a reactivity directed against antigens of molecular weight (M(w)) lower than 50 kDa was detected. Histology revealed traumatic lesions with leukocyte infiltration, and inflammation of the intestinal wall of the infected hens after 105 days of initial infection. The possible influence of the immune and inflammatory response on the population dynamics of the parasite is discussed.

Immunopathology of Dirofilaria immitis Infection

Heartworm disease caused by Dirofilaria immitis affects canine and feline hosts, with infections occasionally being reported in humans. Studies have shown that both dirofilarial antigens and those derived from its bacterial endosymbiont Wolbachia, interact with the host organism during canine, feline and human infections and participate in the development of the pathology and in the regulation of the host’s immune response. Both innate and acquired immune responses are observed and the development of the acquired response may depend on the host and, or on its parasitological status. This review aims at illustrating current research on the role of both D. immitis and Wolbachia, in the immunology and immunopathology of dirofilariosis.

Excretory/secretory antigens from Dirofilaria immitis adult worms interact with the host fibrinolytic system involving the vascular endothelium.

Dirofilaria immitis is the causative agent of canine and feline heartworm disease. The parasite can survive for long periods of time (7 years or more) in the circulatory system of immunocompetent reservoirs, producing usually a chronic inflammatory vascular disease. In addition, the simultaneous death of groups of adult worms can trigger an acute disease characterized by the exacerbation of inflammatory reactions and the emergence of serious thromboembolic events. In the context of the D. immitis/host relationships, the aim of this study was to investigate the interaction between the excretory/secretory antigens from D. immitis adult worms (DiES) and the fibrinolytic system of the host. Using an enzyme-linked immunosorbent assay we showed that DiES extract is able to bind plasminogen and generate plasmin, although this fact requires the presence of the tissue plasminogen activator (t-PA). Moreover, we established that DiES extract enhances t-PA expression in cultured vascular endothelial cells. Additionally, 10 plasminogen-binding proteins from DiES extract were identified by mass spectrometry (HSP60, actin-1/3, actin, actin 4, transglutaminase, GAPDH, Ov87, LOAG_14743, galectin and P22U). The data suggest that DiES antigens interact with the environment of the parasite regulating the activation of the fibrinolytic system of the host with involvement of the vascular endothelium in the process.

Canine and Human Dirofilariosis in the Rostov Region (Southern Russia)

Epidemiological data on canine and human dirofilariosis in the Rostov Region (Southern Russia) are presented. Prevalence of Dirofilaria spp. infections in 795 autochthonous dogs, assessed by the Knott test, was 20.25%. The highest prevalence was found in Novocherkassk (38.3%) and Rostov-on-Don (18.5%), while prevalences were lower in other points of the region. Prevalence of D. repens was 44.7%, prevalence of D. immitis was 30.3%, and coinfections were observed in 25.0% of the dog population. A case finding study carried out during 9 years (2000–2009) revealed 131 cases of human dirofilariosis in the Rostov Region, 129 of subcutaneous dirofilariosis and 2 of pulmonary dirofilariosis. Seroprevalence among 317 healthy blood donors from the Rostov Region was 10.4%, while seroprevalence in policemen living in Rostov city and working in training dogs was 19%. These data show high infection rates of Dirofilaria spp. in both human and dog populations of Rostov, probably because of the existence of favorable conditions for the transmission in this region.