Review of Dirofilaria spp. infection in humans and animals in Iran

Evolution of the parasite

Career mosquitoes receive microfilaria of Dirofilaria while blood feeding from peripheral blood containing the microfilaria of reservoirs. The worm grows and develops in the Malpighian tubules of the mosquito. This is the distinguishing feature of the genus Dirofilaria from others because the others often grow and develop in the flight muscle in chest or fat body cells of mosquito intermediate hosts. After about 2 or 3 weeks (according to environmental factors, especially temperature and mosquito genus), extrinsic incubation period has been passed and infective third-stage larva appears and migrates to the head and proboscis of the mosquito and while blood feeding, by perforating the lower lip proboscis, infects the next host through the created break or by actively perforating the skin. Forth stage larva, adult worms (male and female), and eggs are found in the body of the vertebrate host. The female worm is ovoviviparous. It takes about 7–9 months to observe an adult worm in the pulmonary artery and heart and microfilaria in peripheral blood in an infected dog. The worm life cycle is about 7 years and the reproduction period is 2–5 years in the body of a dog. D. repens genus life cycle is very similar to D. immitis.^[1-3] Microfilaria of D. immitis shows subperiods and this was examined in dog’s blood samples in Tehran^[13,14] and Tabriz^[15,16] and Golestan.^[3,17]

Pathogenesis

Microfilariae have not been observed in peripheral blood of humans and the adult stage is observed 6 months after infection with third-stage larva. Infertile adult and immature D. immitis genus stages have been observed in pulmonary artery and lungs, and in one case, fertile female has been observed in the lungs of a man with lymphoid leukemia. About 65% of pulmonary infection is asymptomatic. Furthermore, cough, chest pain, fever, and inquietude are the symptoms of this disease. D. repens is usually found as painful subcutaneous nodules around or inside the eyes, male genital system, and rarely in lungs. The mature form has also been found in the chest. The subcutaneous nodules are caused by host defensive reactions and they might be soft or hard. These nodules may be painful on palpation or pressure [Figure 1]. Eye infection causes redness, epiphora, blepharitis, pain, and itching. The best and safest way to diagnose infection in humans is to bring out the nodules and study on morphological properties of the worm.^[3,4,6] The life cycle of D. immitis and D. repens shown in [Figures 1 and 2], respectively.^[18,19]

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Figure 1:

Dirofilaria repens life cycle.^[19] https://www.cdc.gov/parasiteWWWs/dirofilariasis/biology_d_repens.html

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Figure 2:

Dirofilaria immitis life cycle.^[18] https://www.cdc.gov/parasites/dirofilariasis/biology_d_immitis.html

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Diagnosis

Clinical signs of dirofilariosis are variable in dogs and include asymptomatic stage to mild symptoms such as cough, immobility, premature fatigue, and severe symptoms such as anemia, cardiac complications, and death. Blood tests by modified Knott’s method, serological tests as ELISA and IFA, and molecular methods (PCR) can detect disease and infected dogs.^[3,4] Farzaneh has reviewed clinical aspects of dirofilariasis in dogs in 1991^[3,20] and Rafii has studied it on practical clinical aspects in 1996.^[3,21] In 2012, Tabrizi stated that cases with dirofilariasis have a higher level of total bilirubin, alkaline phosphatase, and indirect bilirubin in comparison with non-infected cases that show that Dirofilaria can cause side effects on the liver, bile duct, and red blood cells.^[22] Mahdizadeatar has referred to complications and symptoms of the disease, its diagnosis and treatment methods in 1991 and 1992.^[3,23,24] Vahedi (1997) has reviewed various dirofilariasis diagnosis methods in humans and dogs.^[3,25] Eslami et al. (2003) referred to the symptoms and treatment of the disease.^[3,26] Ranjbar-Bahadori and Eslami (2005) compared two methods of diagnosing dirofilariosis, namely, modified Knott’s and ELISA in dogs in Golestan Province.^[3,17] A study by Sharifdini (2012) discovered that the infection rate of D. immitis in dogs more than 2 years old is higher than others in Meshkinshahr, Iran.^[27] Jalali et al. (2016) recognized the outbreak of D. immitis by counter-immunoelectrophoresis besides modified Knott^’s method in 2013.^[28] Zarei et al. accomplished the molecular method based on cytochrome oxidase subunit 1 gene to find out the prevalence of dirofilariasis.^[29] Ranjbar-Bahadori et al. (2007) compared the specificity and sensitivity of two diagnostic methods of D. immitis (modified Knott’s, Antigen Detecting Test Kit), and the McNemar (a statistical test used on paired nominal data) test showed that although the sensitivity of the second one was higher, differences were not significant (P > 0.05).^[30] Either in comparison of ELISA and immune complex disease (ICD) method, they stated that the ICD method is not recommended for the beginning of diagnosis, it may be a valuable secondary way for detecting dirofilariosis in dogs.^[31]

Treatment

The most practical human treatment is the surgical removal of a nodule with a nematode, and chemotherapy is not recommended, since the worm is often dead inside the nodule, and no microfilaria is found in the human peripheral blood. In dogs, thiacetarsamide or melarsomine and ivermectin, milbemycin oxime, or levamisole are used as a filaricide and a microfilaricide respectively.^[3,4,64] In Iran, melarsomine in 2.5 mg/kg and ivermectin in 0.05 mg/kg have been used successfully in the treatment of dirofilariosis in cats.^[3,48]

Control

Control and reduction of human dirofilariasis (HD) depend on the reduction of the infection of its reservoir hosts. Infected dogs should be treated with nematicides after accurate diagnosis. In endemic areas of the disease, treatment of all infected reservoirs (domestic and wild) should be on the agenda. Furthermore, chemoprophylaxis (using drugs for prevention) with the use of ivermectin should be used. It is important to inform and create awareness among dog owners about ways of transmission and preventing it. Reducing the population of mosquitoes and their larvae and personal protection of individuals and dogs against mosquito bites is effective in reducing human and animal infection.^[3,4]

HD in Iran

Among the human cases of the disease, we can mention one case of eye infection of D. repens in Tehran,^[3] one case in Mazandaran,^[32] two cases of subcutaneous infection in Bandar Anzali and Lahijan,^[33] and one case in Karaj (Tehran Province).^[3,34] One rare case of testicular hydrocele infection with D. immitis in Bandar Abbas (Hormozgan Province)^[35] and a subcutaneous dirofilariasis case of an Iranian man who traveled to Belgium have been reported.^[36] Two pulmonary cases (probably D. immitis) based on the observation of coin lesion on radiography and also several cases of subcutaneous dirofilariasis from Ardebil Province have been reported.^[37] There was an unreported eye infection of D. immitis from Gonbad (Mobedi, personal communication).^[3] Maraghi et al. (2006) reported three cases of human infection with the D. repens in Ahvaz, two of which were diagnosed as subcutaneous nodules and the last, as an eye infection.^[38] Tavakolizadeh and Mobedi (2009) presented the first report of ocular dirofilariasis in Tehran, by adult female D. repens worm in 2009.^[39] Parsa et al. reported ocular infection with D. immitis by the molecular characterization method in Kerman in 2020.^[12] Ashrafi et al., 2010, reported a subcutaneous nodule of D. immitis in Gilan that was suspected as cutaneous fascioliasis.^[40] A paranasal subcutaneous nodule of D. repens was reported in Ahvaz from a 31-year-old man.^[41] Tabatabaei et al. (2017), a case with the sub-conjunctival presence of D. immitis was detected in Tabriz.^[42] Maraghi, 2019, discovered breast dirofilariosis with D. repens in a 40-year-old woman resident of Khuzestan.^[43] Furthermore, Mirahmadi et al. (2017) reported ocular dirofilariasis by D. immitis in a 2-year-old child in Chabahar city located at Sistan and Baluchestan Province.^[44] Negahban et al. (2007) presented a case with a subcutaneous nodule of D. immitis in Shiraz that was obtained with the fine needle aspiration method.^[45] Tafti et al. (2010) discovered an ocular dirofilariasis by D. repens in Tehran.^[46]Dirofilaria prevalence in human in Iran reported summarized in [Table 1].

Animal dirofilariosis in Iran

In Iran, animal dirofilariosis has been reported in dogs, jackals, foxes, wolves, and cats. D. immitis has been detected in all the animals above. However, D. repens was only found in dogs and jackals [Table 1].

The prevalence of D. immitis in a global study shows (11.45%) a total weighted prevalence in Iran.^[47]

The first natural infection in stray dogs with D. immitis and D. repens in the country was reported in 1969 in Mazandaran Province, Tonekabon (former Shahsavar).^[11] In that year, infection with D. immitis was seen in a domestic dog imported to Iran from the United States.^[50] Darijani et al. (2009) presented the first report of Dirofilaria in domestic dogs in Kerman.^[51] For the 1^st time, the animal epidemic form of dirofilariosis infection in dogs was reported in the western villages of Meshginshahr, Iran city with 26.7% infection.^[3,52] Alborzi et al. (2010) reported a domestic short hair cat, 2.5 years old in Ahvaz, Iran, with D. immitis confliction.^[53] In a study, the prevalence of D. immitis evaluated with modified Knott’s and immunochromatography was 10% and 11.7%, respectively.^[54]

Various researchers from Fars, Khuzestan, Ardebil, Tehran, West Azerbaijan, East Azerbaijan, Golestan, Garmsar, Gilan, Kerman, Kermanshah, Chaharmahal-Bakhtiari, Sistan and Baluchestan, Hamedan, and Mazandaran Province have reported infections in dogs with D, immitis with the frequency of 0.95–62.8% and in Tehran, Khorasan Razavi, Mazandaran infection with D. repens was reported 1.4–60.8% [Table 2].

In 2004, Moulavi reviewed the micro-anatomy of parasites including D. immitis and D. repens in Iran.^[3,55] In 2005, Lee and Wong introduced a new species Dirofilaria that the infected dog had lived in Germany and Iran before settling in the United States and being diagnosed, making it possible for it to become infected in Iran.^[3,56]

Furthermore, in 1974, Javadian and Macdonald investigated the effect of D. repens species infection on Stegomyia aegypti (Aedes aegypti) mosquito egg production. Thus, one feeding from an infected dog statistically, significantly reduced egg production compared to mosquitoes fed from the blood of an uninfected dog.^[3,57] So far, the species D. immitis has been isolated in cats only once from Tabriz. From 234 cats, microfilaria was obtained in two cases (0/8%) of peripheral blood.^[48] There are two official reports about identifying D. immitis in wolves in East Azerbaijan. The first was a reported infection of one out of five wolves (20%)^[49] and the other was infection of one out of two.^[3]

The first report of jackal infection to D. repens (10%) was in Mazandaran Province.^[3,11] Jackal infection to D. immitis was reported from 2.5% to 57.4% in East Azerbaijan, Ardabil, Khuzestan, Golestan, and Mazandaran Provinces by different researchers [Table 3], but in 2003, the infection rate reported by Meshgi et al. in 11 provinces was 7.5% in total, that in East Azerbaijan, Khuzestan, Golestan, and Mazandaran Provinces, five out of 66 trapped jackals were infected.^[3,58] Meshgi evaluated the prevalence of D. immitis in jackals and foxes in three areas of Iran. The infection rate in the first zone consisting of Gilan, Mazandaran, and Golestan was 3.8%. That of the second one (Zone 2, West Azerbaijan, East Azerbaijan, Ardebil, Markazi, and Esfahan) was 2.5% and the last one (Zone 3, Khuzestan and Hormozgan) was 5%.^[59]

Infection of foxes with D. immitis has been recorded from East Azerbaijan, Ardabil, and Khuzestan Provinces by different researchers with an abundance of 5.7%–50% [Table 4], but in 2003, Meshgi et al. reported the rate of infection in six provinces as 9% in total so that two out of a total of 22 foxes caught in East Azerbaijan and Khuzestan Provinces were infected. They also mentioned an 8.9% infection of the total number of caught wild carnivores, including foxes, jackals, and wolves to D. immitis. Furthermore, Meshgi reported a rate of 8.1% in West Azerbaijan, East Azerbaijan, Ardebil, Markazi, and Esfahan for foxes infected to D. immitis. In the country, the species D. repens has not been isolated from foxes so far.^[3,58]

Dirofilaria infection in Iran

Dissemination of dirofilariasis in Iran: In total, human and animal Dirofilaria infection is reported from eighteen provinces of Iran. D. immitis species has been observed in all of the provinces of the country. In West Azerbaijan, Semnan, Khorasan Razavi, Kermanshah, Hamedan, Qazvin, and Chaharmahal-Bakhtiari Provinces, only animal infection has been reported. In Ardabil, Golestan, Gilan, Kerman, Khuzestan, East Azerbaijan, Fars, Hormozgan, Sistan and Balochistan, Mazandaran, and Tehran, both human and animal infections of this species have been reported. D. repens species was reported in five provinces. While in Khorasan Razavi Province, only animal infection was documented, in Tehran, Mazandaran, Khuzestan, Fars, Ardebil, and Gilan Provinces, both human and animal infections have been found [Table 1].

According to [Table 1], in the seven provinces of Tehran, Gilan, Khuzestan, Fars, Ardebil, Khorasan Razavi, and Mazandaran, human or animal infection to both species of D. immitis and D. repens has been reported. Although in two other independent studies, neither of these two species were found in carnivores of Mazandaran Province.^[3,60,61] Given that Ardabil (Meshginshahr)^{[3,37,52,55,62]} and East Azerbaijan (Tabriz)^[3,15,16,63] were introduced as two zoonotic centers of dirofilariasis (D. immitis), human cases were presented from both and but no cases of D. repens species were found in East Azerbaijan. None of the provinces reported human infection alone with D. immitis. It is worth mentioning that none of the two species of Dirofilaria were previously found in carnivores of Gilan Province.^[3,60]