What is the most likely specimen and organism for a patient with eosinophilia and enlarged spermatic cord after returning from India?

Eosinophilia, which is a high level of eosinophils in the blood, often indicates a parasitic infection, especially in regions where certain helminths or filarial infections are more prevalent. The patient's travel history to India further suggests exposure to tropical and subtropical conditions where such infections are common.

In this case, the presence of an enlarged spermatic cord raises the suspicion for a filariasis infection, commonly caused by Wuchereria bancrofti, which can result in lymphatic filariasis. This condition is characterized by lymphatic obstruction and can lead to swelling in the scrotal region, including the spermatic cord.

Thick blood films are specifically suited for detecting the presence of microfilariae, the larval stage of filarial worms, in the bloodstream. This method allows for a more effective visualization of these small organisms, which can confirm a diagnosis of filariasis.

Other options, such as specimens for Leishmania or Babesia, are less likely because these organisms do not typically cause eosinophilia as a prominent feature and do not correlate with the specific symptoms described (enlarged spermatic cord). Similarly, Trichomonas vaginalis is known to cause urogenital infections but