Biliary parascarosis in a foal

Abstract Migration of Ascaris lumbricoides through the papilla of Vater in humans, and entry into the biliary tree, is well‐recognised. Ascaris suum and Toxocara vitulorum have been recovered from the liver of swine and buffalo. We necropsied a Persian Kurdish filly at age 6 months, weighing ∼100 kg. Death evidently was caused by oleander (Nerium oleander) intoxication. An 8‐cm adult male Parascaris was found at the lobar‐left hepatic bile duct junction. We suggest that the nematode entered anteriorly into the hepatic tree, via the duodenum, major duodenal papilla, bile duct, left hepatic duct and finally the lobar duct. Considering the brief 4‐h elapsed time between death and necropsy, and the 18‐cm distance from the major duodenal papilla to the location of the parasite, we conclude that entry into the biliary tree likely occurred ante‐mortem. We advise consideration of Parascaris infection in differential diagnosis of equine hepatic and pancreatic dysfunction.


BACKGROUND
Infections by Parascaris univalens and P. equorum are common in horses (Nielsen, 2016), with high prevalence among foals aged less than one year (Scala et al., 2021). The life cycle of Parascaris is direct; no intermediate hosts are involved. Mature females occupy the small intestine, where they can shed hundreds of thousands of eggs each day. In the environment, the infective second stage larva (L2) is formed within the egg.
Following ingestion of the infective stage by the host, the released L2 larvae penetrate the small intestinal wall, beginning a somatic migration via the bloodstream through the liver, heart and lungs. From the respiratory system, mucosal secretions transport the larval stage upward to the larynx, to be swallowed. The 4th stage larvae arrive in the small intestine approximately 3 weeks post-infection, resulting in a prepatent period of 10-16 weeks (Nielsen & Reinemeyer, 2018;.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Small intestinal equine ascarids occasionally are recovered in low numbers from the stomach or cecum (Nielsen, 2016). Adult Parascaris in the equine liver or bile ducts have not been reported previously, insofar as the authors are aware. By contrast, there are many reports of Ascaris lumbricoides migration into the bile or pancreatic ducts of humans (John & Petri, 2006). Migration from the intestine through the ampulla of Vater into the biliary system of humans is a wellknown complication of A. lumbricoides infection (Khuroo & Zargar, 1985). In most cases, the worms return to the duodenum in 1-14 days (Das et al., 2007). However, complications such as biliary colic and obstructive jaundice have been reported, consequent to complete or partial obstruction of the bile duct, ascending and pyogenic cholangitis, cholecystolith formation, cholecystitis, intrahepatic abscess and pancreatitis (Fallah & Motahhari, 1998;Sandouk et al., 1997 Oleander leaves were not found in the stomach. Approximately 100 adult Parascaris were found in the small intestine. Liver biliary ducts were examined thoroughly for Fasciola or other trematodes, which were not observed. An 8-cm adult male Parascaris was found at the junction of the lobar and left hepatic ducts ( Figure 1). Evidently, the parasite had entered the hepatic tree at its anterior end, and possible invasion pathway included duodenum, major duodenal papilla, bile duct, left hepatic duct and lobar duct. Considering the brief 4-h interval between death and necropsy, and the 18 cm distance from the major duodenal papilla to the parasite's location, entry into the biliary tree very likely was ante-mortem.
Sections of lung, liver and left ventricle of the heart were submitted for histopathological examination. The tissue specimens were processed routinely and stained with haematoxylin and eosin (H&E).
Stained sections were examined with light microscopy and photographed with an attached digital camera.
Cardiac lesions included severe multifocal necrosis and fragmentation of ventricular cardiomyocytes, microvascular congestion and interfibrillar oedema. Lung tissue revealed severe vascular congestion, interstitial haemorrhage and oedema, and an acute inflammatory (polymorphonuclear) infiltrate. Necrosis and detachment of bronchiolar respiratory epithelium were observed. Liver lesions included cellular degeneration, multifocal coagulative necrosis in acinar periportal and transitional zones, acute inflammation, venous congestion, oedema and distension of sinusoids and predominately mononuclear (lymphocytic) infiltrate (see Figure 2).

DISCUSSION
This first observation of adult Parascaris in the biliary tree of an equine host suggests parasite involvement in hepatopancreatic disease similar to human hepatobiliary and pancreatic duct ascariasis which is known to cause obstructive jaundice, pyogenic cholangitis, cholecystitis and pancreatitis (Fallah & Motahhari, 1998;Sandouk et al., 1997). Only a few reports have described migration of livestock ascarids into host biliary or pancreatic ducts [Ascaris suum in swine (Prchal, 1953) Toxocara vitulorum in buffalo (Srivastava & Sharma, 1981)]. We found just one previous report of Parascaris in an aberrant location in the horse, in the left ventricle of the heart (Pinto & Vaz, 1938).
The rarity of biliary parascarosis in equids could have an anatomical explanation. The horse common hepatic duct (∼5 cm long and 1-1.5 cm wide) is formed at the ventral aspect of the portal fissure by joining of the right and left hepatic ducts. The duct passes obliquely between the two layers of mesoduodenum, opens into the duodenum 12-15 cm from the pylorus, and empties into the hepatopancreatic ampulla. This anatomical arrangement forms a valve that prevents regurgitation of intestinal contents into the duct (Getty, 1975;Khalil et al., 2005).
In swine, A. suum can migrate into the main bile ducts, gallbladder, hepatic bile ducts, pancreatic duct and pancreas. Longer duration of occupation has been linked directly to impairment of hepatic and pancreatic function (Prchal, 1953). In horses, however, only hepatic lesions have been reported in association with migrating Parascaris larvae (Brown & Clayton, 1979). Macroscopic observations included focal haemorrhages and small, white, diffuse or nodular lesions. Histological findings have included eosinophilic and lymphocytic infiltration, portal triad fibrosis, thrombosis and lymphoreticular nodules (Brown & Clayton, 1979). Elevated liver enzymes or clinical signs of liver disease have not been associated with equid parascarosis (Nielsen, 2016). However, biliary obstruction by Parascaris has been suggested as a consideration in differential diagnosis of liver disease (Milne, 1990).

F I G U R E 2 Light microscopic view of lesions in different organs following oleander intoxication. (a) Cardiac muscle shows myofibrillar necrosis (large arrow), sarcoplasmic fragmentation (small arrow), microvascular congestion (arrowheads) and interstitial oedema (asterisk). (b) Lung tissue demonstrates severe vascular congestion (asterisk) and interstitial haemorrhage (large arrows) along with leukocyte infiltration (small arrows) and interstitial oedema. Cellular necrosis and detachment of epithelium (arrowheads) is seen in bronchioles. (c) Liver shows hepatocellular necrosis (large arrow), central venous congestion (asterisk), oedema and distension of sinusoids (small arrows) along with mononuclear infiltration of leukocytes (arrowheads). Haematoxylin & Eosin, Magnification
The proximate cause of death in this report was oleander intoxication. Nerium oleander is an evergreen shrub that is cultivated worldwide as an ornamental plant. In ancient India, oleander was called Kajamaraka, 'the herb that makes the horse die' . Oleander poisoning can be fatal for humans and animals; the lethal dose (LD) of dried leaves varies by species. Lethal doses have been reported by body weight in cattle (50 mg/kg), goats (100 mg/kg) and sheep (250 mg/kg) (Ceci et al., 2020;Aslani et al., 2007;Oryan et al., 1996). Equids are more susceptible to oleander poisoning than ruminants; a single dose of 30 mg/kg was fatal for donkeys in an experimental study (Rezakhani & Maham, 1994).
Considering that fatal ingestion of oleander leaves can occur at 0.005% of an animal's body weight (Butler et al., 2016), the foal in the present report needed to consume just 0.5 kg of dried plant material.
It is believed that outmigration of A. lumbricoides from the intestinal lumen can be provoked by certain drugs and anaesthetic agents (John & Petri, 2006;Sanai & Al-Karawi, 2007). Since oleander contains a variety of glycosides that include neriifolin, thevetin A and B and oleandrin (Bandara et al., 2010), aberrant migration of Parascaris in the present instance could have been associated with glycoside content of the host's ingested food. Whether the Parascaris nervous system is susceptible to oleander glycoside toxicity is not known, although flavonol glycosides of ssazainfoin (Onobrychis viciifolia) can inhibit migration of Haemonchus contortus larvae in vitro (Barrau et al., 2005). Additionally, cyanogenic glycosides of some plants have been associated with anti-nematodal activity (Chitwood, 2002).
The recommended dose of fenbendazole is 7.5 mg/kg body weight, but resistance of gastrointestinal nematodes to anthelmintic compounds such as benzimidazoles is a common problem in Iran (Nemati et al., 2019). In particular, fenbendazole treatment failure was observed in three Iranian provinces namely Hamedan, Yazd and Azarbaiajan Sharghi (Ashrafzadeh et al., unpublished). Most regional farmers are not aware of this serious issue, and nonprescribed treatment with anthelmintics seems to be important for emergence of anthelmintic resistance . Hence, in the present case, the recent anthelmintic dose could have had a sublethal effect on the parasite.
Microscopic examination of heart, lung and liver revealed histopathology that is consistent with oleander intoxication in experimental studies (Aslani et al., 2007;Oryan et al., 1996;Khordadmehr et al., 2017) and naturally occurring oleander toxicosis in animals (Ceci et al., 2020;. Relevant findings have included myocardial necrosis and haemorrhage; effusion in pleural, peritoneal, and pericardial cavities; hepatocellular necrosis and hepatitis; gastrointestinal haemorrhage and oedema; pulmonary congestion; and renal infarction, necrosis, and congestion Renier et al., 2013;Bazargani et al., 2008). However, when sudden death occurs in oleander-intoxicated animals, gross or microscopic lesions are observed rarely, due to insufficient elapsed time for development of an extensive inflammatory response (Aslani, 2018). The observed inflammatory foci in the liver parenchyma may have resulted from Parascaris larval migration in the organ rather than the effects of the ingested toxic plant.

CONCLUSION
Herein, the first observation of an adult Parascaris in the liver of a horse is presented. Although finding one adult without associated pathology does not allow casual conclusion it suggested that parascarosis should be considered in the differential diagnosis of foals and horses with hepatopancreatobiliary disease.

ACKNOWLEDGEMENT
Authors are grateful to Dr. Dennis F. Lawler (Illinois State Museum, USA) for English revision of the text.

FUNDING INFORMATION
The authors received no funding.

CONFLICT OF INTEREST STATEMENT
The authors declare that they have no competing interests.

ETHICS STATEMENT
Not applicable.

DATA AVAILABILITY STATEMENT
All data generated or analysed during this study are included in this published article and its additional files.