# Survival and infectivity of Paragonimus westermani Metacercariae in soy sauce–marinated crayfish

## TL;DR

This study shows that marinating crayfish in soy sauce with high salt does not reliably kill lung fluke parasites, which can still infect people and cause disease.

## Contribution

The study demonstrates that traditional marination methods may not inactivate P. westermani metacercariae, highlighting a food safety risk.

## Key findings

- P. westermani metacercariae can survive in soy sauce with up to 20% NaCl for several weeks.
- Borderline metacercariae still retain infectivity with 33.7% worm recovery in dogs.
- Complete inactivation requires 60 days in 10% NaCl or 30 days in 20% NaCl soy sauce.

## Abstract

Paragonimus westermani, a zoonotic lung fluke, causes respiratory symptoms resembling tuberculosis. In Asia, human infections typically occur through the consumption of raw or marinated freshwater crabs or crayfish containing P. westermani metacercariae. With increasing global food trade and occasional exposure during international travel, cases have been reported in non-endemic regions, raising significant food safety concerns. In this study, naturally infected freshwater crayfish (Cambaroides similis) were collected from Haenam, South Korea. Crayfish were marinated in soy sauce containing either 10 % or 20 % sodium chloride (NaCl) and stored at 4 °C for 1–60 days. P. westermani metacercariae were recovered at each time point and morphologically classified as viable, borderline (uncertain viability), or dead. To assess infectivity, 100 P. westermani metacercariae from each group were orally inoculated into beagle dogs (n = 3 per group), and worm recovery was assessed after 12 weeks. After 14 days of marination, the survival rates of P. westermani metacercariae were 83.3 % in 10 % NaCl and 2.0 % in 20 % NaCl soy sauce. Complete inactivation occurred after 60 days in 10 % NaCl and 30 days in 20 % NaCl. Infectivity tests showed worm recovery rates of 82.5 % (viable), 33.7 % (borderline), and 0 % (dead). These findings indicate that even high-salt, cold-storage marination does not guarantee parasite inactivation. Viable P. westermani metacercariae can persist in marinated crayfish under commonly used culinary conditions. These results underscore the risk of foodborne lung fluke infections and emphasize the need for clearer public health guidance regarding the consumption of undercooked or inadequately processed freshwater crustaceans.

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•Paragonimus westermani metacercariae survive in soy sauce–marinated crayfish.•High-salt marination (up to 20 % NaCl) does not ensure parasite inactivation.•Infectivity persists even after partial morphological degradation.•Borderline metacercariae can infect all animals, with ∼30 % worm recovery.•Traditional marination methods pose a risk of foodborne paragonimiasis.

Paragonimus westermani metacercariae survive in soy sauce–marinated crayfish.

High-salt marination (up to 20 % NaCl) does not ensure parasite inactivation.

Infectivity persists even after partial morphological degradation.

Borderline metacercariae can infect all animals, with ∼30 % worm recovery.

Traditional marination methods pose a risk of foodborne paragonimiasis.