Zoonotic Filariasis

Abstract

SUMMARY Filariae of animals, especially those of mammals, often infect humans and typically produce cryptic infections. These “zoonotic” infections have been reported from virtually all parts of the world including temperate zones. Infections may be symptomatic or not, and the parasites are found in surgical tissue biopsy specimens or, more rarely, are removed intact from superficial sites such as the orbit or conjuctivae. Typically, these worms tend to occupy tissue sites similar to those occupied in the natural animal host, with the exception of the eyes. Many kinds of filariae have been isolated from humans, including species of Dirofilaria, Brugia, Onchocerca, Dipetalonema, Loaina and Meningonema. Worms have been found in subcutaneous tissues, the heart and lungs, lymphatics, the eye, and the central nervous system. Specific identification of these filariae is based on their morphological features in histologic sections. Unfortunately, some of these worms cannot be identified even at the generic level. There are other species of filariae, presumed to be zoonotic, which produce patent infections in humans but are poorly and incompletely known. These include Microfilaria semiclarum and Microfilaria bolivarensis. It is probable that almost any filaria parasitizing animals can, under proper circumstances, infect humans and undergo some degree of development. Undoubtedly, additional species of filariae will continue to be isolated from humans in the future.

Ribosomal DNA second internal transcribed spacer sequence studies of Culicid vectors from an endemic area of Dirofilaria immitis in Spain

“…In animal reservoirs, the parasite induces a serious and potentially fatal pathology that includes damages in the vascular endothelium, lungs, and heart (Vezzoni and Venco 2001). In the human host, D. immitis cause, in some instances, benign pulmonary nodules that can be confused in radiology with cancer or other serious pathological conditions (Orihel and Eberhard 1998). Different species of culicid mosquitoes of the genera Culex, Culiseta, Aedes, Anopheles, and Coquilletidia have been incriminated in the transmission of D. immitis based on captures made in endemic areas (Cancrini and Kramer 2001).…”

A human case of subcutaneous dirofilariasis caused by Dirofilaria repens in Vietnam: histologic and molecular confirmation

“…Compared with other Dirofilaria worms, the D. repens is a robust parasite with a maximum female and male body length of 17 cm and approximately 7 cm, respectively and a diameter of 650 μm and 450 μm, respectively, have been reported (Orihel and Eberhard 1998). In cases of human infection, D. repens measuring up to approximately 660 μm in diameter have been observed (Gutierrez 1984;.…”

“…However, depending on the quality of the histological sections, some of these morphological features may not be absolute. In addition, identification of the causative Dirofilaria agent is also closely correlated with geographic areas affected with individual Dirofilaria species (Orihel and Eberhard 1998).…”

“…The morphological features of individual parasites are as follows: body length and width, thickness of the laminated cuticle, the presence and/or absence of external longitudinal ridges on the surface of the cuticle, lateral chords, and number and type of circumferential muscle cells (Orihel and Eberhard 1998;Ratnatunga and Wijesundera 1999;Pampiglione et al 1999). However, depending on the quality of the histological sections, some of these morphological features may not be absolute.…”

“…In its definitive hosts, D. repens can easily be identified by its morphological features; however, in nondefinitive hosts such as humans, these filarial worms may be more difficult to identify using morphological and histological characteristics, particularly when the clinical samples that have been removed from the subcutaneous nodules have become damaged and/or immature worms were found (Pampiglione et al 1999). Serological examination is a useful tool for differentiating between D. repens and D. immitis infections (Santamaría et al 1995), while elevated levels of IgM, IgG and IgE have been used in patients exposed to other Dirofilaria species (Simón et al 1997;Orihel and Eberhard 1998). In order to overcome the limitations associated with serological and histological examinations, polymerase chain reaction (PCR)-based methods capable of differentiating between Dirofilaria species have been developed (Favia et al 1996(Favia et al , 1997a(Favia et al , b, 2000Rivasi et al 2006;Marušić et al 2008).…”