**Core Concept**
Inclusion conjunctivitis is a type of conjunctivitis caused by certain bacterial and viral pathogens, characterized by the presence of inclusion bodies in the conjunctival epithelial cells. This condition is often associated with sexually transmitted infections.

**Why the Correct Answer is Right**
Chlamydia trachomatis is the primary causative agent of inclusion conjunctivitis, particularly in newborns who acquire the infection from their mother during birth. This bacterium belongs to the Chlamydiaceae family and is known to cause a range of ocular and systemic infections. The inclusion bodies, which are actually elementary bodies of the Chlamydia organism, can be visualized in the conjunctival epithelial cells using a Giemsa stain or immunofluorescence. The pathogenesis of inclusion conjunctivitis involves the attachment of Chlamydia to the conjunctival epithelial cells, followed by the formation of inclusion bodies and the release of infectious elementary bodies.

**Why Each Wrong Option is Incorrect**
**Option B:** Chlamydia psittaci is primarily associated with psittacosis, a respiratory disease transmitted from birds to humans, and is not a common cause of inclusion conjunctivitis.
**Option C:** Herpes simplex virus is a common cause of herpetic keratitis and epithelial keratitis, but not inclusion conjunctivitis.
**Option D:** Gonorrhoea, caused by Neisseria gonorrhoeae, is a sexually transmitted infection that can cause conjunctivitis, but it is not associated with inclusion bodies in the conjunctival epithelial cells.

**Clinical Pearl / High-Yield Fact**
Inclusion conjunctivitis is often bilateral and can be accompanied by systemic symptoms such as fever and respiratory distress in newborns. Treatment involves the use of antibiotics, such as azithromycin or erythromycin, and supportive care to manage symptoms.

**✓ Correct Answer: A. Chlamydia trachomatis**