Human pulmonary dirofilariasis: a review

Molecular characterization of canine filarioids in a previously non-endemic area of Rio de Janeiro State, Brazil

Dirofilaria immitis is the causative agent of canine heartworm disease, a severe health problem in dogs, especially in coastal areas of tropical and subtropical regions of the world. We employed molecular methods to investigate the occurrence of canine infection by filarioids in five municipalities of Baixada Fluminense (Magé, Duque de Caxias, Guapimirim, Nova Iguaçu, and São João de Meriti), a non-endemic area of Rio de Janeiro State, Southeast Brazil. A total of 110 canine blood samples collected from 2017 to 2018 and positive for microfilariae at the modified Knott's test were screened by cPCR targeting DNA fragments of the 12S rDNA gene for filarial nematodes. Seventy-seven samples (70%) tested positive at the molecular analysis. Of these, 72 were identified as D. immitis and 5 (4.5%) as Acanthocheilonema reconditum. Dirofilaria repens was not detected in the studied municipalities of Baixada Fluminense. This is the first record of D. immitis and A. reconditum in the Baixada Fluminense region, Rio de Janeiro State, Brazil. The prevalence of D. immitis cases in the five municipalities suggests the establishment and maintenance of its enzootic cycle in the studied region, which indicate vulnerability to the occurrence of epidemic cycles and, possibly, human cases.

Overview on Dirofilaria immitis in the Americas, with notes on other filarial worms infecting dogs

Canine dirofilariosis in the Americas is primarily caused by Dirofilaria immitis, a mosquito-borne filarial worm infecting dogs, which may also infect and cause disease in other mammalian hosts, including humans. Morphological and molecular evidence gathered in the past decades suggest that other Dirofilaria spp. may infect dogs in the American continent, though the actual taxonomic identity of them still needs to be elucidated. In addition, filarial worms belonging to distinct genera have also been reported in dogs in this part of the world, including Acanthocheilonema reconditum, Cercopithifilaria bainae, and Onchocerca lupi. Among these, O. lupi is a species of major clinical significance, which has been reported not only in dogs, but also in cats and humans in North America. The present article provides a current overview on canine dirofilariosis in the Americas, with notes on other filarial worms infecting dogs. It also provides some insights into outstanding research questions that should be responded to fill some of the several knowledge gaps related to this group of parasites in this continent.

Filarial nematodes with zoonotic potential in ring-tailed coatis (Nasua nasua Linnaeus, 1766, Carnivora: Procyonidae) and domestic dogs from Iguaçu National Park, Brazil

Iguaçu National Park, which contains the largest remnant of Atlantic Forest in southern Brazil and Iguaçu Falls as one of its main visiting points, is a year-round attraction for thousands of domestic and international tourists. Ring-tailed coatis are generalist, opportunistic carnivores that benefit from human association. These animals are the most abundant carnivores in this park, where they come into close contact with tourists and the resident population around the park. Moreover, as the park is surrounded by human dwellings, free roaming domestic dogs are frequently present, favoring the exchange of pathogens with wild animals. Wild carnivores are known to be infected with several pathogens, from viruses to arthropods, some of them passed on by domestic carnivores. Among the nematodes that infect wild carnivores, those of the Onchocercidae family are of concern due to their zoonotic potential. The objective of this research was to assess the prevalence of filarial nematodes in coatis and dogs in Iguaçu National Park, as well as the potential impact of infection on host health and body condition. To this end, 75 coatis and 50 adult dogs were captured in the aforementioned area. Seven species of filarioids, Dirofilaria immitis, Dirofilaria repens, Acanthocheilonema reconditum, Brugia sp., Mansonella sp. and two undetermined species, confirmed by histochemical tests, were diagnosed in the area. Knott's concentration test in coatis and dogs showed a prevalence of 81.6% and 16.0%, respectively. Seven microfilarial morphotypes were diagnosed in the coatis and two morphotypes were found in the dogs. A specific immunoassay test for Dirofilaria immitis revealed the presence of D. immitis infection in 1.33% of the coatis and 22% of the domestic dogs. The parasitic infection had negligible effects on the body condition of both dog and coati hosts, but an increase was found in eosinophil counts in coatis with filarial infection, as well as decreases in hematocrit and hemoglobin in the infected domestic dogs. These findings represent new locality and host records for all the filarioids diagnosed in the area of this study, with some of the diagnosed parasites, given their zoonotic potential, representing a health risk for park visitors and the local population.

Parasitic pneumonia and lung involvement

Parasitic infestations demonstrated a decline in the past decade as a result of better hygiene practices and improved socioeconomic conditions. Nevertheless, global immigration, increased numbers of the immunocompromised people, international traveling, global warming, and rapid urbanization of the cities have increased the susceptibility of the world population to parasitic diseases. A number of new human parasites, such as Plasmodium knowlesi, in addition to many potential parasites, have urged the interest of scientific community. A broad spectrum of protozoal parasites frequently affects the respiratory system, particularly the lungs. The diagnosis of parasitic diseases of airway is challenging due to their wide varieties of clinical and roentgenographic presentations. So detailed interrogations of travel history to endemic areas are critical for clinicians or pulmonologists to manage this entity. The migrating adult worms can cause mechanical airway obstruction, while the larvae can cause airway inflammation. This paper provides a comprehensive review of both protozoal and helminthic infestations that affect the airway system, particularly the lungs, including clinical and roentgenographic presentations, diagnostic tests, and therapeutic approaches.

Dogs, cats, parasites, and humans in Brazil: opening the black box

Dogs and cats in Brazil serve as primary hosts for a considerable number of parasites, which may affect their health and wellbeing. These may include endoparasites (e.g., protozoa, cestodes, trematodes, and nematodes) and ectoparasites (i.e., fleas, lice, mites, and ticks). While some dog and cat parasites are highly host-specific (e.g., Aelurostrongylus abstrusus and Felicola subrostratus for cats, and Angiostrongylus vasorum and Trichodectes canis for dogs), others may easily switch to other hosts, including humans. In fact, several dog and cat parasites (e.g., Toxoplasma gondii, Dipylidium caninum, Ancylostoma caninum, Strongyloides stercoralis, and Toxocara canis) are important not only from a veterinary perspective but also from a medical standpoint. In addition, some of them (e.g., Lynxacarus radovskyi on cats and Rangelia vitalii in dogs) are little known to most veterinary practitioners working in Brazil. This article is a compendium on dog and cat parasites in Brazil and a call for a One Health approach towards a better management of some of these parasites, which may potentially affect humans. Practical aspects related to the diagnosis, treatment, and control of parasitic diseases of dogs and cats in Brazil are discussed.

Dirofilariosis in the Americas: a more virulent Dirofilaria immitis?

Dirofilarioses are widespread diseases caused by filarioid nematodes (superfamily Filarioidea) of the genus Dirofilaria, which are transmitted by a plethora of mosquito species. The principal agent of canine dirofilariosis in the Americas is Dirofilaria immitis, which may also occasionally infest humans, resulting in pulmonary nodules that may be confounded with malignant lung tumours. Because human cases of dirofilariosis by D. immitis are relatively frequent in the Americas and rare in Europe and other eastern countries, where Dirofilaria repens is the main causative agent, the existence of a more virulent strain of D. immitis in the Americas has been speculated. Recently, a case of human ocular infestation by Dirofilaria sp. was diagnosed in Pará State, northern Brazil, where canine heartworm dirofilariosis is endemic. The nematode was shown to be morphologically and phylogenetically related to D. immitis but it was genetically distinct from reference sequences, including those of D. immitis infesting dogs in the same geographical area. This finding raised questions regarding the aetiology of human dirofilariosis in the Americas, since information on the genetic makeup of filarioids infesting dogs and humans is meagre. Further studies would be needed to better characterize filarioids infesting dogs, wild animals, and humans in the Americas and to assess the existence of a more virulent D. immitis strain in this continent. Finally, the competence of different culicid species/strains from Europe and the Americas as vectors of Dirofilaria species should be investigated. Such studies would help us to understand possible variations in transmission patterns and even to predict possible scenarios that may emerge in the future, with the introduction of non-endemic Dirofilaria species/strains in free areas through importation of infested animals, vectors, or both.

Human intraocular filariasis caused by Dirofilaria sp. nematode, Brazil

A case of human intraocular dirofilariasis is reported from northern Brazil. The nematode was morphologically and phylogenetically related to Dirofilaria immitis but distinct from reference sequences, including those of D. immitis infesting dogs in the same area. A zoonotic Dirofilaria species infesting wild mammals in Brazil and its implications are discussed.

Detection of Dirofilaria immitis (Nematoda: Filarioidea) by polymerase chain reaction in Aedes albopictus, Anopheles punctipennis, and Anopheles crucians (Diptera: Culicidae) from Georgia, USA

Potential mosquito vectors of Dirofilaria immitis (Leidy) (Nematoda: Filarioidea), the causative agent of dog heartworm in the southeastern region of the United States, were collected with CDC light traps and gravid traps in seven counties in the state of Georgia, USA. The presence of D. immitis in these mosquitoes was detected by polymerase chain reaction using species-specific primers for the D. immitis surface or cuticular antigen. Overall, 1,574 mosquitoes of 13 species in seven genera were collected; 92% of the specimens were Aedes albopictus (Skuse), Aedes vexans (Meigen), or Anopheles punctipennis (Say). Ae. albopictus, An. punctipennis, and Anopheles crucians Wiedemann were positive for D. immitis DNA. Ae. albopictus had the highest maximum likelihood rate of infection (2.30%; 95% confidence interval [CI] = 1.15-4.00%) followed by An. crucians (1.38%: 95% CI = 0.04-6.93%), and An. punctipennis (0.85%: 95% CI 0.03-4.29%). The detection of D. immitis DNA in the heads and thoraxes of Ae. albopictus (0.40%; 95% CI = 0.12-2.02%) indicates that these mosquitoes can support the development of D. immitis to the infective stage 3 larvae.

Canine vector-borne diseases in Brazil

Canine vector-borne diseases (CVBDs) are highly prevalent in Brazil and represent a challenge to veterinarians and public health workers, since some diseases are of great zoonotic potential. Dogs are affected by many protozoa (e.g., Babesia vogeli, Leishmania infantum, and Trypanosoma cruzi), bacteria (e.g., Anaplasma platys and Ehrlichia canis), and helminths (e.g., Dirofilaria immitis and Dipylidium caninum) that are transmitted by a diverse range of arthropod vectors, including ticks, fleas, lice, triatomines, mosquitoes, tabanids, and phlebotomine sand flies. This article focuses on several aspects (etiology, transmission, distribution, prevalence, risk factors, diagnosis, control, prevention, and public health significance) of CVBDs in Brazil and discusses research gaps to be addressed in future studies.

Experimental Infection of Dirofilaria immitis in Raccoon Dogs

Canine heartworm (Dirofilaria immitis) is a nematode that naturally parasitizes in the pulmonary arteries and the right ventricle of domestic dogs (Canis familiaris) as final hosts. Japanese raccoon dogs (Nyctereutes procyonoides viverrinus) also are known to be susceptible to infection by the parasite. However, prevalence of this infection among free-ranging raccoon dogs is low and so is the worm burden. To examine the susceptibility of the raccoon dog to D. immitis infection, 3 raccoon dogs and 2 beagles were inoculated 4 times with 25 third-stage larvae (L3s) of D. immitis at 3-wk intervals. Worms were recovered from 2 raccoon dogs and both domestic dogs. The average percentage of recovery (2.3%) of the raccoon dogs was almost 10 times lower (24.5%) than that of the domestic dogs, but there was no significant difference in the body length of worms recovered from 2 types of hosts. To examine microfilaremia, 2 raccoon dogs were infected with 100 L3s. Microfilaremia was observed for 180 days postinoculation (PI) but disappeared at about 300 days PI. The raccoon dog was mildly susceptible to infection with D. immitis, but surviving worms developed and matured normally.

Dirofilaríase pulmonar humana no Estado do Rio de Janeiro, Brasil: relato de um caso

Relata-se caso de dirofilaríase pulmonar humana em paciente com 45 anos de idade, proveniente do Estado do Rio de Janeiro, Brasil. A radiografia torácica evidenciou nódulo pulmonar solitário localizado no lóbulo inferior esquerdo, mimetizando neoplasia. Dirofilaríase pulmonar humana deveria ser investigada em nódulos pulmonares não malignos e de etiologia não conclusiva.

[Prevalence of canine filariasis by Dirofilaria immitis and Dipetalonema reconditum in Maceió, Alagoas State, Brazil]

A survey on the prevalence of Dirofilaria immitis and Dipetalonema reconditum was conducted in 1,519 dogs from Maceió and two coastal areas in the State of Alagoas, Northeast Brazil, from 1995 to 1999, by testing for microfilariae in blood. All blood samples were from exclusively domiciled dogs with a known history, showing that the infections were autochthonous, confirming transmission of canine filariasis in these areas. In Greater Metropolitan Maceió, 15 (1.3%) microfilaremic dogs were detected with D. immitis and 15 (1,3%) with D. reconditum. In the southern coastal area there was an estimated prevalence of 12.7% for D. immitis. D. immitis and D. reconditum microfilaria were 298.1 micrometer and 249.2 micrometer long and 7.3 micrometer and 4.4 micrometer wide, respectively. A Witness immunotest that detects D. immitis antigen was used to confirm parasitological results and reveal occult dirofilariasis cases. Of the total 6,579 females examined, 8 (0.1%) Culex quinquefasciatus were observed to be naturally infected with D. immitis larvae. These results proved dirofilariasis transmission in Maceió and demonstrated D. reconditum in the same geographic area.

Prevalence of dirofilarial infection in raccoon dogs in Japan

The raccoon dog (Nyctereutes procyonoides viverrinus) is known to acquire canine heartworm (Dirofilaria immitis) infection. We surveyed the prevalence of heartworm infection in free-ranging raccoon dogs in the Nishi-Tama (Tokyo) and Kanagawa areas of Japan. A total of 75 raccoon dog carcasses, including 29 animals from the Nishi-Tama area and 46 from the Kanagawa area, were necropsied between 1992 and 1993. Eight out of 75 raccoon dogs were found to be infected (overall 10.7%). The prevalence of infection was 6 and 16% in Nishi-Tama and Kanagawa, respectively. Microfilarial production was observed in the uterus of one female adult dog.

[Canine heartworm on São Luís Island, Northeastern Brazil: a potential zoonosis]

A survey on the prevalence of canine heartworm was conducted in 1, 495 dogs from Maranhão Island, State of Maranhão, Northeastern Brazil, from 1991 to 1994, by testing for microfilariae in blood. Of the total, 1,358 (12.8% of which were infected) were dogs with no known history; they included 1,265 homeless animals (10.3% with microfilariae) and 93 kept by owners at the time the survey was conducted (37.8% of which were infected). Prevalence is high among dogs captured and/or living along the seashore. Examples of such high coastal prevalence rates were found in Olho d'Agua and Calhau (46% and 43%, respectively). The search for microfilariae in blood samples of 137 exclusively domiciliary dogs with a known history showed that 43% of these animals were infected, confirming transmission of heartworm on the island. This was the first survey formally published on canine dirofilariasis in Northeastern Brazil. Since D. immitis is infective to man and prevalence of the parasite is high, particularly along the coast of Maranhão Island, human cases of dirofilariasis may be expected. Local physicians should consider this parasite among the possible causes of solitary lesions in humans living in this area.

Human pulmonary dirofilariasis: analysis of 24 cases from São Paulo, Brazil

STUDY OBJECTIVE

To present the clinical, radiologic, and pathologic aspects of 24 cases of human pulmonary dirofilariasis (HPD) from São Paulo, Brazil.

DESIGN

Retrospective study of 24 patients with a confirmed diagnosis of HPD over a 14-year period (from February 1982 to June 1996).

SETTING

Thoracic Surgery and Pulmonary Division, University of São Paulo and Hospital Albert Einstein, São Paulo, Brazil.

RESULTS

Seventeen patients were male (70.1%) and seven were female (29.9%). Their mean age was 51.4 years. Fifty-four percent of the patients were asymptomatic and 75% had a well-circumscribed noncalcified peripheral subpleural pulmonary nodule on the chest radiograph and thoracic CT scan, located preferentially in the lower lobes. The diagnosis was made after thoracotomy and wedge resections in 16 patients, by videothoracoscopy in six, after a pleural biopsy in one, and after necropsy in one. The pathologic examination of all the nodules revealed a central zone of necrosis, surrounded by a narrow granulomatous zone and peripherally by fibrous tissue. Pulmonary vessels exhibit varying degrees of endarteritis. In all cases, a dead worm, usually necrotic and fragmented, was found.

CONCLUSIONS

A subpleural, noncalcified pulmonary nodule in the appropriate clinical and epidemiologic setting should alert the clinician, radiologist, or pathologist to the possibility of Dirofilaria. HPD should be considered in the differential diagnosis of pulmonary nodules.