Kuwait Zoo Chimpanzee Dies of Hydatid Cyst as First Genetic Confirmation of Echinococcus Genotype G1 in the Species

A 32-year-old female common chimpanzee that died at the Kuwait Zoo in September 2025 after months of declining health has yielded the first genetically confirmed case of Echinococcus granulosus sensu stricto genotype G1 in a chimpanzee, and the first DNA-sequenced identification of any Echinococcus genotype in Kuwait. The animal, which had been imported from Nigeria 25 years earlier and had remained apparently healthy for most of its time in the zoo, succumbed after showing severe respiratory distress, and a post-mortem examination revealed a cyst roughly the size of a handball embedded in the hepatic umbilical fissure.

According to the authors, the chimpanzee had shared its cage with an adult male and was fed vegetables and fruits brought from the local market. Zoo records showed three episodes of respiratory distress between November 2024 and July 2025, and during the final six months of its life the animal became anorectic, depressed and lethargic, with pale conjunctival mucous membranes, a slightly distended abdomen and alopecia. Caretakers initially diagnosed gastrointestinal disturbances and bloat, and administered a liver tonic, stomachic and multivitamins without improvement. At the late stage of disease the chimpanzee was in a miserable condition, struggling to breathe, often gasping and grinding its teeth in pain.

The post-mortem findings pointed to severe hepatic disease. The cyst was lodged in the umbilical fissure of the liver, where it pressed on the bile duct, the pyloric opening of the stomach and the portal blood vessels. The liver itself appeared enlarged and congested, the bile duct and gall bladder were distended, and the subcutaneous fatty layer was deeply yellow in color, indicating severe jaundice. When the thick-walled cyst was incised, small thin-walled vesicles emerged; three of these fluid-filled daughter cysts were sent to the laboratory for identification.

Microscopic examination of the fluid and sediment from one daughter cyst revealed protoscoleces bearing a crown of characteristic hooks, the diagnostic larval armature of Echinococcus. One daughter cyst and several protoscoleces were preserved in 70 percent ethanol for molecular work. The team extracted total genomic DNA from a single protoscolex and amplified a fragment at the 3′ end of the mitochondrial nad1 gene, a target long favored for differentiating Echinococcus genotypes and well represented in public sequence databases. The polymerase chain reaction used the forward primer JB11 and the reverse primer Cyclo-trnNR, with an annealing temperature of 45 degrees Celsius, and an additional internal primer, JB12, assisted sequencing. Products were purified and cycle-sequenced, then run on a SeqStudio Genetic Analyzer, and the contiguous sequence was assembled with Sequencher software.

The resulting nad1 sequence was 765 nucleotides long and has been deposited in GenBank under accession number QB140010. A BLAST search against previously sequenced isolates showed that the sequence was almost identical to multiple G1 genotype sequences of E. granulosus sensu stricto, differing by only a single nucleotide from sequences derived mostly from sheep and cattle in Turkey, Iran and Armenia, and by only two nucleotides from G1 sequences from distant regions and different intermediate hosts, such as pigs in Argentina. The authors interpret this pattern as evidence of a highly homogenized genome in E. granulosus, resulting from extensive movement of its definitive and intermediate hosts around the world over a long period of time.

The identification carries broader significance because of how the E. granulosus species complex is organized. Based on genetic data, E. granulosus sensu lato, the causative agent of cystic echinococcosis, comprises genotypes traditionally designated G1 through G10, currently assigned to five distinct species: G1 to G3 form E. granulosus sensu stricto, G4 is E. equinus, G5 is E. ortleppi, G6 and G7 are E. intermedius, and G8 to G10 are E. canadensis. Among these, E. granulosus sensu stricto, particularly genotype G1, the sheep genotype, is the most common and is responsible for most human cystic echinococcosis cases worldwide. The parasite’s life cycle involves canid definitive hosts, while herbivorous and omnivorous mammals serve as intermediate hosts harboring the larval hydatid cyst. Humans are physiologically suitable intermediate hosts but ecologically dead ends, and non-human primates can likewise be involved as intermediate hosts, though they are unlikely to serve as a source of infection for definitive hosts.

The report is also the first molecular characterization of Echinococcus in Kuwait, despite the country being an area where cystic echinococcosis is endemic in humans and animals. The authors note that no molecular analysis of Echinococcus genotypes had previously been conducted in the country. As far as they know, cystic echinococcosis has not been reported in non-human primates in the wild, likely because of the difficulty of sampling and examining wild animals, but many publications have documented the disease in captive primates, including rhesus macaques, pig-tailed macaques, red-tailed guenons, ring-tailed lemurs, red-ruffed lemurs, baboons and great apes. A chimpanzee in a zoo in California was previously reported to be infected with a hydatid cyst that perforated its abdominal wall, but no clinical or pathological details were provided and the cyst was not genotyped. Genetic data for E. granulosus sensu lato in non-human primates remain very limited; besides the present case, genotype G1 has been reported in ring-tailed lemurs and a red-tailed guenon, while genotype G5 was detected in one ring-tailed lemur in the United Kingdom and genotype G4 was documented in both a red ruffed lemur and a ring-tailed lemur.

How the Kuwait chimpanzee became infected could not be determined with certainty, and the authors outline three possibilities. The animal may have been exposed through the feces of canid final hosts, although screening of wild canid feces in the zoo for taeniid eggs using a flotation technique returned negative results. Alternatively, the chimpanzee might have acquired the infection in Nigeria before its arrival in Kuwait 25 years ago; little is known about the duration of infection and the timing of symptom onset in non-human primates, but hydatid cysts have been detected in experimentally infected vervet monkeys and baboons 15 to 28 months after infection, and assuming the incubation period in chimpanzees is comparable to that in humans, it could last many years. The authors also note their previous report of echinococcosis in a vervet monkey born and raised in the same zoo, which suggests infection after arrival in Kuwait is possible. A third possibility is contaminated food brought from the local market, since vegetables and fruit contaminated with taeniid eggs from markets in Europe have been shown to pose a threat to captive primates, and the authors suggest the same may be true in Kuwait.

The epidemiological context in Kuwait favors transmission between dogs and livestock. Stray dogs infected with E. granulosus are considered the most likely source of contamination of vegetables, and an earlier study found that 23 percent of examined stray dogs in Kuwait were infected with the parasite. Among livestock, sheep have been documented as the most important intermediate hosts in the country, and the finding of genotype G1, the sheep genotype, in the chimpanzee is consistent with that conclusion. Genotype G1 is common across Middle East countries, where socioeconomic factors, human activities and sheep husbandry practices facilitate transmission. In Kuwait, most sheep are free-range and graze in extensive contact with shepherd dogs in the desert and remote areas around cities, while stray and guard dogs often access livestock farms and backyard gardens. Mutton is the preferred meat, home slaughtering is common particularly on religious and social occasions, and Bedouins feed dogs with sheep entrails; the bodies of dead sheep are often left in the desert, making them available to dogs and wild canids alike. The authors suggest this scenario may result in a sylvatic life cycle of the parasite, but they emphasize that this point needs further investigation.

The report also underscores the public health dimension of environmental contamination. High prevalence of E. granulosus infection in dogs has been found to correlate with frequently reported human cystic echinococcosis cases in Bedouin communities, and an earlier estimate placed the incidence of human cystic echinococcosis in Kuwait at 3.6 cases per 100,000, a figure its authors considered an underestimation of the true incidence. In the present case, the large size of the cyst and its position in the umbilical fissure of the liver were the determinants of the lesions and clinical signs, producing a typical case of hepatic cystic echinococcosis comparable to that observed in humans. Because E. granulosus infection usually remains asymptomatic for months or years and symptoms appear at the latest stages of disease, antemortem diagnosis is difficult and the prognosis is poor. The authors therefore recommend that apparently healthy captive primates in zoos be examined serologically, and by radiology where necessary, so that cases of cystic echinococcosis can be diagnosed early enough for suitable medical intervention, and they call for regular monitoring of the prevalence of Echinococcus in livestock and in domestic and wild canids in Kuwait.

Subject of Research: Molecular identification of Echinococcus granulosus sensu stricto genotype G1 causing a fatal hydatid cyst in a chimpanzee at the Kuwait Zoo

Article Title: First molecular characterization of Echinococcus granulosus sensu stricto genotype G1 from a common chimpanzee (Pan troglodytes) in the Kuwait Zoo

Article References: El-Azazy, O. M. E., Abouelella, A. G., Aryan, F. A. M., Kinsella, J. M., Tahrani, L. M. A., & Tkach, V. V. (2026). First molecular characterization of Echinococcus granulosus sensu stricto genotype G1 from a common chimpanzee (Pan troglodytes) in the Kuwait Zoo. Acta Parasitologica, 71(6), Article 242. https://doi.org/10.1007/s11686-026-01422-x

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01422-x

Keywords: cystic echinococcosis, Echinococcus granulosus, genotype G1, hydatid cyst, chimpanzee, Kuwait Zoo, nad1 gene, zoonosis, molecular characterization, environmental contamination, stray dogs, Kuwait