Medical Science Test 1 Nddc Scholarship

The *Ixodes* tick (commonly known as the deer tick or black-legged tick) is a well-known vector for several pathogens. While it is most famous for transmitting the bacteria that cause Lyme disease, it is also the primary vector for *Babesia*, a malaria-like protozoan parasite that infects red blood cells and causes Babesiosis. *Leishmania donovani* is transmitted by sandflies, and *Giardia lamblia* is typically contracted through the ingestion of contaminated water. The *Ixodes* tick provides a necessary environment for *Babesia* to complete its life cycle before being passed to a mammalian host during a blood meal.

Chagas' disease, also known as American Trypanosomiasis, is caused by the protozoan parasite *Trypanosoma cruzi*. It is primarily transmitted to humans through the faeces of triatomine bugs (also known as 'kissing bugs'). Nifurtimox and Benznidazole are the standard antiparasitic drugs used to treat the infection, especially during the acute phase. *Naegleria* is associated with primary amoebic meningoencephalitis, *Schistosoma* causes Schistosomiasis (bilharzia), and *Wucheria bancrofti* is a roundworm that causes lymphatic filariasis (elephantiasis). The link between *Trypanosoma cruzi* and the specific treatment of Chagas' disease is a fundamental concept in tropical medicine.

Cryptococcus neoformans is an encapsulated yeast, Candida albicans is a common opportunistic fungus, and Tinea nigra is a superficial fungal infection of the skin. Chlamydiae, however, are a group of obligate intracellular bacteria. While they were once historically confused with other organisms due to their unique life cycle, they possess bacterial characteristics such as a cell wall containing peptidoglycan, DNA and RNA, and susceptibility to antibiotics like tetracycline, which do not affect fungi.

Adenoviruses, Papovaviruses (such as HPV), and Poxviruses (such as Variola) all contain DNA as their primary genetic material. Caliciviruses, which include the Norovirus (responsible for many outbreaks of gastroenteritis), are actually positive-sense, single-stranded RNA viruses. They are non-enveloped and have a characteristic cup-shaped morphology under electron microscopy, which is where their name, derived from the Latin 'calix' for cup, originates.

Reoviruses, Orthomyxoviruses (influenza), and Deltaviruses all utilise RNA for their genetic blueprints. Herpesviruses, which include Herpes Simplex Virus (HSV) and Varicella-Zoster Virus (VZV), belong to a large family of enveloped, double-stranded DNA viruses. They are known for their ability to establish lifelong latent infections in their hosts, periodically reactivating to cause symptoms.

Poxviruses, Adenoviruses, and Herpesviruses all possess linear, double-stranded DNA. Papovaviruses (a group that includes Papillomaviruses and Polyomaviruses) are distinct because their double-stranded DNA is circular rather than linear. This circular structure is essential for their replication cycle within the nucleus of the host cell and for their ability to integrate into the host's genome in some instances of oncogenic transformation.

Togaviruses, Retroviruses, and Picornaviruses all have single-stranded linear RNA genomes. Bunyaviruses are unique among this group because their genome is segmented into three parts (Small, Medium, and Large) and the RNA is circular in configuration within the virion, rather than being a single linear strand. This segmentation allows for genetic reassortment, similar to what is seen in influenza viruses.

The Tzanck test is used for the rapid diagnosis of vesicular lesions caused by Alphaherpesviruses, specifically Herpes Simplex Virus type 1 (HSV-1), type 2 (HSV-2), and Varicella-Zoster Virus (VZV). It involves taking a scraping from the base of a fresh vesicle. HHV-8 (Human Herpesvirus 8), also known as Kaposi's Sarcoma-associated Herpesvirus, does not typically present with the same type of vesicular lesions and its diagnosis relies on biopsy and PCR rather than Tzanck smear cytology.

E. coli is the leading cause of UTIs, followed by other Gram-negative rods like Klebsiella and Pseudomonas (the latter often seen in hospital-acquired infections). Haemophilus species, such as *Haemophilus influenzae*, are primarily associated with respiratory tract infections, meningitis, and epiglottitis. While they are Gram-negative, they rarely colonise the urinary tract and are not considered standard uropathogens.

The Optic nerve (II) provides vision, the Oculomotor nerve (III) controls most eye movements and the pupil, and the Abducens nerve (VI) controls the lateral rectus muscle for outward eye movement. The Facial nerve (VII), while it controls the muscles for closing the eyelid (orbicularis oculi) and lacrimation (tearing), does not directly move the eyeball or provide vision. It is primarily the nerve of facial expression and taste for the anterior two-thirds of the tongue.