Epidemiology of Hydatidosis in Iraq: A Subject Review

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Introduction

Hydatidosis or Cystic echinococcosis is a chronic zoonotic disease caused by the larval form of Echinococcus granulosus sensu lato. It is an undeniable fact that it has significant impact on human health, livestock production and national economies, especially in the developing world where increased contact of dogs with livestock makes it an important vector for parasite transmission (World Health Organization, 2023) [10]. E. granulosus has domestic and wild canids as definitive hosts and herbivorous mammals, especially sheep, goats, cattle, and camels, as intermediate hosts. Humans can become an accidental intermediate host when parasite eggs are ingested through contaminated food or water or by direct contact with infected dogs. The embryos pass through the portal circulation; most of them end up in hydatid cysts in the liver and lungs after ingestion (Deplazes et al., 2017) [4]. Iraq is one of endemic countries of CE in the Middle East. Livestock farming (where it is still practiced), home slaughtering, inadequate disposal of the infected meat and many roamers dogs are responsible for the continuous transmission for decades. This led to hydatidosis being considered as a still relevant public health and veterinary problem despite the advancement of diagnostic imaging and surgical management (Eckert & Deplazes, 2004; WHO, 2023) [5]. The disease has been reported in all parts of Iraq, such as the governorates of Baghdad, Basrah, Duhok, Erbil, Sulaymaniyah, Kirkuk, Diyala, Karbala, Thi-Qar, Wasit, Maysan, Nineveh, and Al-Anbar. The prevalence of the disease is variable, but it is still endemic in both rural and urban communities, indicating persistent maintenance of transmission between definitive and intermediate hosts (Saida & Nouraddin 2011 and Abdulhameed et al. 2018) [8, 1].

Epidemiology of hydatidosis in Iraq is related to livestock production systems. Sheep are the most important intermediate host as they are highly susceptible to infection; sheep are the most abundant livestock species in many governorates in Iraq. Domestic and stray dogs are important definitive hosts, cattle, goat, buffaloes and camels are also contributing factors in maintaining the parasite life cycle. Infected dogs can spread eggs to the environment and soil, vegetables and water, thus allowing the transmission of the infection to humans and animals (Deplazes et al., 2017; To establish this, a retrospective epidemiological study was carried out in Baghdad Province, which showed that about 70% of all cases were female, and that the most common age group was 31-40. Housewives were the largest occupational group affected, indicating that activities within the household and close contact with domestic animals may be risk factors for exposure. The predominant organ affected was the liver, followed by lungs, kidneys and spleen (Al-Yasari et al., 2020) [2].

In contrast, a hospital-based back-calculation study in the Basrah Province concluded that CEC is still a significant public health issue. The majority of patients were female and the majority of infections were in adults aged 21-30 years. Nearly half of the cases diagnosed were hepatic cysts and about one-quarter were pulmonary. Abdulhameed et al. (2018) [1] noted that underestimation of the actual burden of disease in southern Iraq is likely due to incomplete surveillance systems.

Previous epidemiological studies in northern Iraq showed that levels of infection were high in stray dogs and that these dogs were very important in maintaining the transmission of parasites. Adult E. granulosus worms were found in almost half of the stray dogs examined and infections occurred most frequently among farmers, laborers and housewives. The present results further confirm the significance of controlling the infection of the dog as an integral part of hydatidosis control in Iraq (Saida & Nouraddin, 2011) [8].

Epidemiology of Hydatidosis in Iraq Cystic echinococcosis (CE) or hydatidosis continues to be one of the most neglected zoonotic diseases in Iraq that inflicts significant disease burden on both man and domestic animals. The larval stage of Echinococcus granulosus sensu lato is the primary cause of the disease and a domestic cycle has been established with dogs as the definitive hosts and herbivorous animals – sheep, goats, cattle, buffaloes, and camels – as intermediate hosts. Human infection is accidental and occurs when parasite eggs are ingested by humans through food, water, vegetables or soil. Environmental, agricultural and socio-economic conditions in Iraq lead to continuous environmental transmission of parasites and this is why Iraq is classified as one of the Endemic countries in the Middle East (Deplazes et al., 2017; World Health Organization, 2023) [4].

Hydatidosis is geographically distributed in Iraq in a varied manner between governorates. Nearly all provinces have reported cases of the disease, including Baghdad, Basrah, Duhok, Erbil, Sulaymaniyah, Nineveh, Kirkuk, Diyala, Wasit, Thi-Qar, Maysan, Babylon, Karbala, Najaf, and Al-Anbar. Sheep husbandry is common and the animals contact dogs easily and are generally widely distributed in the northern governorates, which is why the prevalence in these governorates is generally high. In a similar manner, the southern provinces are still endemic due to the traditional animal husbandry approach, the presence of free roaming dogs and the lack of biosecurity in slaughterhouses. Available data suggest that hydatidosis is a public health issue at the national level and not a localised disease, although there are regional differences (Abdulhameed et al., 2018) [1]. Human epidemiological studies in Iraq have indicated that all age groups are affected by CE, but most surgically confirmed cases are in adults as hydatid cysts grow slowly and often are clinically silent for many years. The study conducted at the hospital in Baghdad Province showed that the percentage of female patients was about 70% and the highest frequency of disease was found in the age group of 31-40 years. Housewives were the largest category of occupation, indicating that exposure to contaminated vegetables, water or domestic dogs within the home might be a risk factor for infection. The same study revealed that there was more infection in the liver than in other organs such as pulmonary, splenic and renal cysts which were seen in fewer numbers (Al-Yasari et al., 2020) [2].

A significant disease burden is still present in southern Iraq as well. During a retrospective study of surgically treated patients in Basrah Province between 2005 and 2015, 748 cases were confirmed, estimated to be approximately 4.5 cases per 100,000 people per year. The liver was the most common organ, which is expected since the parasite embryo is filtered through the portal circulation and pulmonary circulation. The authors have suggested that the actual incidence rate is likely under-estimated as many infections are asymptomatic and there are very few surveillance systems based on community surveillance and most are based on hospital based surgical records (Abdulhameed et al., 2018) [1].

Livestock are a key factor in the epidemiology of hydatidosis in Iraq. Sheep are considered as the main intermediate host due to its susceptibility to E. granulosus and its prevalence in rural areas of Iraq. Infection has been reported in cattle, goats, buffaloes and camels, but is more prevalent in some than others depending on species, age, management system and geographic location. Investigations by abattoirs have always revealed hydatid cysts in slaughtered animals in the liver and lungs, indicating that active transmission is occurring within livestock herds and that significant economic losses are occurring as result of organ condemnation (Deplazes et al., 2017) [4].

Dogs continue to be the primary definitive host that is responsible for environmental contamination with E. granulosus eggs. Infected offal left behind in home slaughter operations or less than proper control in slaughterhouses is a common source of infestation by free roaming and stray dogs. Infested dogs will excrete thousands of parasite eggs per day that will pollute pastures, vegetables, water and pets' homes. As a result, humans and livestock are exposed to the infection by ingesting accidentally the embryonated eggs. This domestic dog–livestock cycle is the main way that hydatidosis is maintained in Iraq (Eckert & Deplazes, 2004; Hydatid disease is still endemic in Iraq due to multiple risk factors. These include lack of veterinary supervision at home slaughter, lack of proper disposal of infected viscera, unrestricted access of dogs to slaughter wastes, poor hygiene, lack of health education and lack of routine dog deworming programs. Exposure is higher in rural areas due to the tendency of livestock to be kept close to people within households, thus offering more opportunities for transmission from dogs to livestock and livestock to people. Limited veterinary infrastructure and poor public awareness also impede disease control, due to socioeconomic conditions (Budke et al., 2006; Deplazes et al., 2017) [3, 4]. Nevertheless, despite modern advances in diagnostic imaging, surgery and anti-parasitic chemotherapy, hydatidosis remains a significant cost to Iraq's livestock sector and healthcare system. Human disease may cause extended hospital stays and surgery, while livestock infections typically lead to loss of productivity and edible organs at slaughter due to condemnation. The results highlight the importance of implementing integrated surveillance programmes that incorporate a One Health approach and integrate veterinary medicine, public health, environmental sanitation and community education to limit transmission and enhance disease control (Budke et al., 2006; Public Health and Economic Impact Hydatidosis is a serious public health problem in Iraq due to its chronic nature, the prolonged clinical course and need for surgical intervention in many patients. Hepatic and pulmonary cysts often require hospitalization, further imaging, antiparasitic treatment, and surgical removal, making these cysts a significant burden on our health-care system. The disease burden is underestimated as the cysts grow slowly and are not detected until years after infection, resulting in a delay in symptom recognition. The economic impact is not limited to human diseases. The effects of hydatid infection in the livestock include condemnation of infected livers and lungs at meat inspection, loss of carcass value, decrease in productivity and losses for the farmers and meat industry. These losses are exacerbated by health care costs, loss of productive labor force, and surveillance and control expenses on a national level. Economics has also been reported to be affected in other endemic Middle Eastern countries, and therefore hydatidosis is an both a veterinary and public health problem (Budke et al., 2006; Torgerson & Macpherson, 2011; WHO, 2023) [3, 9].

Control Strategies A One Health strategy must be adopted in Iraq to control hydatidosis, combining human health, veterinary medicine, environmental management, and public education. Intervention measures that aim at humans only will not interrupt the transmission of Echinococcus granulosus, since multiple hosts are involved in its life cycle. Rather, more holistic control strategies should aim to minimize the spread of infection in dogs, prevent contact of livestock with infected dogs, enhance slaughterhouse sanitation, and raise awareness of the community (Deplazes et al., 2017; World Health Organization, 2023) [4].

Treatment of dogs every 4-6 weeks with praziquantel in endemic communities is one of the most effective measures against the control. Frequent deworming significantly cuts down on environmental contamination of E. granulosus eggs and the life cycle of the parasite is disrupted. Coordinated municipal and veterinary programs are also crucial to managing stray dog populations. These measures should be supplemented by legal measures to block access of dogs to slaughterhouse waste and infected animal parts (Hameed and Ahmed, 2021 ; WHO, 2023) [6].

The second key factor in disease control is an improvement in slaughterhouse infrastructure. All slaughtered animals should be subject to veterinary inspection, and infected parts of the animal should be safely incinerated or buried as opposed to being thrown away where dogs can reach them. In some governorates in Iraq, home slaughter which takes place during religious and social functions is still a frequent practice and is continuing to contribute to the transmission of parasites, despite veterinary supervision of modern slaughtering sheds. Therefore, improvement of meat inspection services and implementation of slaughterhouse legislation is crucial for the decrease in infection of definitive hosts. Another key aspect of prevention is health education. Farmers, shepherds, butchers, slaughterhouse employees, school students and rural households should be the focus of educational campaigns. Hand hygiene after handling a dog, washing of vegetables before eating, safe disposal of infected offal should become part of the public awareness programme, along with regular deworming of dogs. Insecticide intervention has been found to increase knowledge of the transmission of parasites and to promote practices to decrease the risk of infection in endemic areas (Budke et al., 2006; Hameed et al., 2021; WHO, 2023) [7, 3].

Nationwide surveillance systems integrating human, veterinary and environmental information should be given high priority in future epidemiological studies in Iraq. The molecular epidemiology of the use of DNA sequencing and genotyping should be used in the identification of E. granulosus genotypes in circulation and to understand transmission between livestock, dogs and humans. Spatial Epidemiology and Geographic Information Systems (GIS) can also be used to determine disease hotspots and direct efforts to control disease. Further, the creation of a national registry of hydatidosis cases would enhance estimates of disease burden and help to monitor intervention programs over time (Deplazes et al., 2017 and Hameed et al., 2021) [4, 6].

Conclusion

Hydatidosis is still an issue of importance with regard to zoonosis and a longstanding public health problem in Iraq. The disease is found throughout the country with dogs and livestock, especially sheep, playing a role in its maintenance. There is close association with human infection and rural living, livestock keeping, home slaughter, poor disposal of infected offal and control of stray dog populations. While the introduction of diagnostic imaging and surgical management has helped improve patient outcomes, there is still a lack of consistent implementation of preventative measures, which leads to transmission. The epidemiological evidence presented in this article is a call to take measures to strengthen surveillance, improve veterinary services, deworm canines on a regular basis, regulate the slaughterhouses, and educate the community extensively. A coordinated One Health approach by doctors, veterinarians, public health officials, environmental agencies and local communities are needed to help decrease the burden of hydatidosis in Iraq. Continued molecular epidemiological studies and national surveillance programs will provide greater knowledge of disease transmission and help guide evidence-based control measures.