Infection Status of Hydatid Cysts in Humans and Sheep in Uzbekistan

Cystic echinococcosis (CE) is a global zoonotic larval tapeworm disease which is caused by the hydatid cyst of Echinococcus granulosus. The human is infected as an intermediate host of Echinococcus granulosus. The major mode of human infection is ingestion of its eggs by direct fecal contact of infected dogs or eating contaminated food or water [1]. Human infection is known as CE with other names of hydatid disease or hydatidosis. Human CE occurs mainly in the liver and lungs [2]. Therefore, the liver and lungs are major target organs of the disease screening. However, most of CE patients have no symptoms at the early stage of infection, and realize its subjective symptoms suddenly when the cyst is big or complicated. In such a circumstance, most of CE patients require emergency intervention. It is difficult to screen or estimate the symptomless infected people before appearance of the emergent medical episode even in endemic areas.

Several parameters are used instead to evaluate endemicity or disease occurrence in an endemic area. They are annual incidence of patients, infection rate of sheep or other mammals, and infection rate of dogs. Each parameter suggests its epidemiological significance for echinococcosis transmission in a certain area [2-4]. Uzbekistan is known endemic of CE with other middle Asian or Mediterranean countries [3]. Official reports figured 1,435 human cases in 2000 and 819 in 2001 in whole Uzbekistan, and the sheep were reported with high positive rates about 60% at the same time [3]. In order to investigate recent disease burden of CE in Uzbekistan, we collected patient data from the national networked hospitals of the Republican Research Center of Emergency Medicine in 2002-2010. Also all of the sheep were monitored of the hydatid cyst in their liver and lungs at an abattoir in Tashkent, the capital of Uzbekistan, from July 2009 to June 2010.

In the 14 networked emergency medicine hospitals, a total of 8,014 patients received surgical intervention of CE during 2002-2010 (Table 1). All of them were diagnosed and treated under emergency condition. Since Uzbek surgeons are familiar with CE management, the number of patients could be a nearly real estimation, confirmed and managed by the 14 emergency hospitals. The true national figure of clinical CE patients must add numbers of CE patients cared by other hospitals to the 8,014 patients.

Table 1.

Numbers of surgical CE patients by the Republican Research Center of Emergency Medicine branches in 14 states of Uzbekistan, 2002-2010

Sheep are slaughtered every day in Tashkent. A total of 22,939 heads were slaughtered and grossly screened of their liver and lungs after devisceralization by a veterinarian. The hydatid cyst was recovered from the liver of 479 (2.1%) and from the lungs of 340 (1.5%) sheep, and total 819 (3.6%). Some of the sheep were infected both in the liver and lungs, and also other organs, but those details were not considered in this screening.

The Republican Sanitation and Epidemiology Center of Uzbekistan is officially monitoring and reporting patient numbers based upon reports from the 14 State Sanitation and Epidemiology Centers. The official data reported 1,438 cases in 1998, 1,435 in 2000, and 819 in 2001 [3]. The data were official numbers of CE patients in Uzbekistan, but they must have been underestimated. That is because only a part of the patients of emergency hospitals or other hospitals who were recognized at the local township health centers were included in the data. Many of them were dropped due to no collaboration system between the hospitals and the state Sanitation and Epidemiology Centers. The figure of 2,966 patients in 2010 was the minimum confirmed number of CE in Uzbekistan in the year. Furthermore, symptomless patients of early CE (ECE) must be much more than the confirmed figure. Some of ECE cases may become overt emergency patients after several years but some are not [5]. Torgerson et al. [3] suggested 3 times of more patients than that of official report in Uzbekistan. Since the official report counted about 1,000 cases in a year, the real number of cases were suggested about 3,000 and total 12,520 cases were estimated [3]. However, the network hospitals of emergency medicine recognized about 3,000 patients every year. There are many other hospitals which can take care of CE in whole country. Therefore, if we suppose that the transmission of E. granulosus is in an epidemiologically stable natural equilibrium, newly infected cases must be far more than 3,000 every year in Uzbekistan. The real population of patients must be much more than 12,520 because every infected patient carries the CE for several years without symptoms.

When a patient of ECE is diagnosed, he or she can be treated medically [1]. However, it is difficult and impractical to detect symptomless ECE. If a system for diagnosis of ECE is established, emergency surgical intervention could be reduced in Uzbekistan. The system should be supported by both serodiagnostic test and radiological or ultrasound images [1,6]. The serodiagnostic system using ELISA is essential and critical for upgraded management of both CE and ECE [7,8].

The Republican Research Center of Emergency Medicine Samarkand Branch summarized records of CE patients by the involved organs (Table 2). The liver (69.0%) and the lungs (22.2%) were commonly involved, and 7 (1.5%) were cerebral CE. Other organs were involved but not frequently. Multiorgan infection might have been but not specified in this summary. The findings by organs were same in general as previously described [1,2].

Table 2.

Number of patients who received surgery of cystic echinococcosis in the Republican Research Center of Emergency Medicine, Samarkand Branch, 2005-2010

Between 1990 and 2002, the sheep was reported with cyst positive rates from 45.1% to 62.2% in Uzbekistan [3]. Also high rates of cattle (24.3-45.5%), pigs (6.0-8.0%), camels (25.4-35.0%), and donkeys (32.0-38.5%) were reported positive [3]. Our positive rate of 3.6% was much lower than that of the previous report. At present, it is not easy to explain the big difference. Just it is inferred that our study examined all sheep at an abattoir in Tashkent for one year while the previous ones were sampled in most hyperendemic local regions. It is difficult to directly compare data of separate studies of different locality, sampling, and timing. Although the positive rate was 3.6%, it is an enough evidence of active transmission of E. granulosus in Uzbekistan.

The infection rate of dogs is another important parameter in epidemiology because the dogs seed eggs of E. granulosus, and the eggs from them are infecting humans and sheep. The dogs were reported as 7.9% positive among village dogs and 20.1% among farm dogs in Uzbekistan [3]. The population of infected dogs in a community should be estimated to monitor accurately the infection force of E. granulosus. Since Uzbekistan is the most frequent country of imported CE cases in Korea, accurate and updated epidemiological parameters are required for proper management of the disease [9].

In conclusion, the 8,014 emergency patients in 2002-2010 confirm that CE is an important infectious disease in Uzbekistan. Also the infection rate of 3.6% among sheep is an evidence of active transmission of E. granulosus between sheep and dogs. CE is a helminthic zoonosis of public health priority in Uzbekistan.