Zoonotic Diseases Practice Questions

Q: Transovarian transmission is a feature of which disease?

Scrub fever. **Explanation** **Transovarian transmission** refers to the passage of a pathogen from a female vector to its offspring via the eggs. This mechanism allows the pathogen to persist in the environment even in the absence of a vertebrate host. **Why Scrub Typhus (Scrub Fever) is correct:** Scrub typhus is caused by *Orientia tsutsugamushi* and is transmitted by the bite of the larval stage (chigger) of **Leptotrombidium mites**. Since only the larvae feed on mammals, the bacteria must be passed from the adult female mite to her eggs (transovarian transmission) and subsequently to the larvae to maintain the life cycle. The mite acts as both the vector and the primary reservoir. **Why the other options are incorrect:** * **Epidemic Typhus (*Rickettsia prowazekii*):** Transmitted by the human body louse. The louse dies from the infection and does not pass the bacteria to its offspring. * **Endemic Typhus (*Rickettsia typhi*):** Transmitted by the rat flea (*Xenopsylla cheopis*). While it can persist in flea populations, transovarian transmission is not the primary epidemiological feature compared to scrub typhus. * **Trench Fever (*Bartonella quintana*):** Also transmitted by the human body louse; no transovarian transmission occurs. **High-Yield Clinical Pearls for NEET-PG:** * **Vector for Scrub Typhus:** Larval mite (Chigger). * **Pathognomonic Sign:** An **eschar** (a black, necrotic scab) at the site of the chigger bite. * **Weil-Felix Reaction:** Scrub typhus shows a positive reaction with **OX-K** (negative for OX-2 and OX-19). * **Drug of Choice:** Doxycycline is the gold standard for all rickettsial diseases.

Q: A patient presents with chills, fever, body rashes, delirium, and subsequent coma, which began shortly after a louse bite. A provisional diagnosis of vasculitis due to rickettsial infection is considered. Which of the following is the most likely causative agent?

Rickettsia prowazekii. **Explanation:** The clinical presentation of fever, chills, a characteristic rash, and neurological symptoms (delirium/coma) following a **louse bite** is classic for **Epidemic Typhus**, caused by ***Rickettsia prowazekii***. **Why Option C is Correct:** *Rickettsia prowazekii* is transmitted by the **human body louse** (*Pediculus humanus corporis*). The pathogen multiplies in the gut of the louse and is excreted in feces; infection occurs when the host rubs louse feces into the bite wound. A hallmark of this disease is the "typhus state," where patients progress from delirium to stupor and coma (the word *typhos* means "cloudy" or "stuporous"). The underlying pathology is widespread **vasculitis** due to the organism's tropism for endothelial cells. **Why Other Options are Incorrect:** * **A. *Rickettsia typhi*:** Causes Endemic (Murine) Typhus. It is transmitted by **rat fleas**, not lice, and generally presents with milder symptoms. * **B. *Rickettsia rickettsii*:** Causes Rocky Mountain Spotted Fever. It is transmitted by **ticks** and is characterized by a rash that typically starts on the wrists and ankles before spreading centrally. * **C. *Rickettsia akari*:** Causes Rickettsialpox. It is transmitted by **mites** and is characterized by a localized eschar at the bite site followed by a papulovesicular rash. **NEET-PG High-Yield Pearls:** * **Brill-Zinsser Disease:** A recrudescent (latent) form of Epidemic Typhus that occurs years after the primary infection with *R. prowazekii*. * **Weil-Felix Reaction:** A heterophile agglutination test used for diagnosis. *R. prowazekii* reacts with **OX-19**. * **Drug of Choice:** Doxycycline is the gold standard treatment for all rickettsial infections.

Q: Rocky mountain spotted fever is caused by which species of Rickettsia?

Rickettsia rickettsii. **Explanation:** **Rocky Mountain Spotted Fever (RMSF)** is caused by ***Rickettsia rickettsii***. It is the most severe and frequently reported rickettsial illness in the Western Hemisphere. The organism is transmitted to humans through the bite of infected **Ixodid (hard) ticks**, specifically *Dermacentor variabilis* (American dog tick) and *Dermacentor andersoni* (Rocky Mountain wood tick). **Analysis of Options:** * **Rickettsia rickettsii (Correct):** The causative agent of RMSF. It characteristically involves the vascular endothelium, leading to a classic triad of fever, headache, and a centripetal rash (starting on wrists/ankles and spreading to the trunk). * **Rickettsia typhi:** Causes **Endemic (Murine) Typhus**, transmitted by the rat flea (*Xenopsylla cheopis*). * **Rickettsia conorii:** Causes **Boutonneuse fever** (also known as Kenya tick typhus or Indian tick typhus). It is characterized by a "tache noire" (black eschar) at the site of the tick bite. * **Rickettsia akari:** Causes **Rickettsialpox**, transmitted by the house mouse mite (*Liponyssoides sanguineus*). **High-Yield NEET-PG Pearls:** 1. **Rash Pattern:** In RMSF, the rash is **centripetal** (periphery to center). In Epidemic Typhus (*R. prowazekii*), the rash is **centrifugal** (trunk to extremities, sparing palms/soles). 2. **Weil-Felix Reaction:** This is a heterophile agglutination test using *Proteus* antigens. RMSF shows a positive reaction with **OX-19 and OX-2**. 3. **Drug of Choice:** **Doxycycline** is the gold standard treatment for all rickettsial infections, regardless of the patient's age. 4. **Obligate Intracellular:** Rickettsiae are obligate intracellular gram-negative bacilli that do not stain well with Gram stain; **Giemsa or Gimenez stains** are preferred.

Q: Which of the following is NOT true regarding Chlamydia psittaci?

It causes non-gonococcal urethritis.. ### Explanation **Why Option B is the Correct Answer:** *Chlamydia psittaci* is primarily a respiratory pathogen and does **not** cause non-gonococcal urethritis (NGU). NGU is caused by **_Chlamydia trachomatis_** (Serotypes D-K), *Ureaplasma urealyticum*, and *Mycoplasma genitalium*. *C. psittaci* causes Psittacosis (Ornithosis), a zoonotic atypical pneumonia characterized by fever, headache, and a dry cough. **Analysis of Incorrect Options:** * **Option A:** *C. psittaci* is indeed endemic in birds (parrots, pigeons, poultry). Humans get infected by inhaling dried bird excreta or dust from feathers. * **Option C:** Like all Chlamydiae, *C. psittaci* is an **obligate intracellular parasite**. It cannot grow on artificial agar but can be grown in "specified laboratory media" such as **cell cultures** (e.g., McCoy or HeLa cells), yolk sacs of embryonated eggs, or experimental animals. * **Option D:** **Tetracyclines (Doxycycline)** are the first-line treatment for all Chlamydial infections, including Psittacosis. Macrolides (Azithromycin) are an alternative. **High-Yield Clinical Pearls for NEET-PG:** * **Horder’s Spots:** A rare clinical sign of Psittacosis consisting of rose-colored spots on the face. * **Splenomegaly:** Unlike most atypical pneumonias, Psittacosis is frequently associated with splenomegaly. * **Diagnosis:** Serology (Complement Fixation Test or Microimmunofluorescence) is the gold standard. * **Inclusion Bodies:** *C. psittaci* produces diffuse, irregular inclusion bodies (LCL bodies) that **do not contain glycogen** (unlike *C. trachomatis*) and are therefore **iodine-negative**.

Q: Which of the following species of Brucella tends to produce a more acute and aggressive presentation?

B. melitensis. **Explanation:** Brucellosis is a zoonotic infection caused by small, Gram-negative coccobacilli. While all species cause a similar clinical syndrome (undulant fever, arthralgia, and hepatosplenomegaly), their virulence and severity vary significantly based on the species. **Why B. melitensis is correct:** **Brucella melitensis** (found in goats and sheep) is the most virulent and common species causing human brucellosis worldwide. It is associated with a **more acute, severe, and aggressive clinical presentation**, often leading to higher rates of complications like osteomyelitis and endocarditis. Its high pathogenicity is attributed to its ability to evade the host immune system more effectively than other species. **Analysis of Incorrect Options:** * **B. suis (Pigs):** This species is the second most virulent. It tends to cause a chronic infection characterized by **suppurative (abscess-forming) lesions** in organs like the liver and spleen. * **B. abortus (Cattle):** This is the most widespread species but generally causes a **milder, more insidious** disease with fewer complications compared to *B. melitensis*. * **B. canis (Dogs):** This species is the least common cause of human infection and typically results in a **mild or subclinical** illness. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** Bone marrow culture (more sensitive than blood culture). * **Standard Serology:** Standard Agglutination Test (SAT); a titer of >1:160 is significant. * **Castaneda’s Medium:** A specialized biphasic medium used for blood cultures to reduce the risk of laboratory-acquired infections. * **Treatment:** The WHO recommends **Rifampicin + Doxycycline** for 6 weeks. For neurobrucellosis or endocarditis, a triple regimen including an Aminoglycoside is used.

Q: Stalactite growth in ghee broth is due to?

Yersinia pestis. **Explanation:** **Yersinia pestis** (the causative agent of Plague) exhibits a characteristic growth pattern in liquid media, specifically **Ghee broth** or broth with a layer of oil. When inoculated, the bacteria grow as delicate, hanging pellicles that extend downwards from the surface, resembling **stalactites**. This occurs because the organism is non-motile and tends to grow in chains or clumps that adhere to the oil droplets at the surface before sinking slowly. **Analysis of Options:** * **Haemophilus influenzae:** Requires X factor (hemin) and V factor (NAD) for growth. On solid media, it shows "satellitism" around *S. aureus*, but it does not produce stalactite growth. * **Corynebacterium diphtheriae:** Characteristically grown on Loeffler’s Serum Slope or Potassium Tellurite Agar. In liquid media, it may form a surface pellicle, but it lacks the specific stalactite morphology. * **Treponema pallidum:** This is an obligate spirochete that **cannot be grown on artificial culture media**. It is maintained via serial passage in rabbit testes (Nichol’s strain). **High-Yield Clinical Pearls for Yersinia pestis:** 1. **Safety Pin Appearance:** Shows bipolar staining with Wayson or Giemsa stain. 2. **Temperature Regulation:** It is non-motile at 37°C but **motile at 25°C** (though some strains remain non-motile). 3. **Culture:** Grows on Blood Agar as "Copper-beaten" or "Hammered silver" colonies. 4. **Vector:** Primarily transmitted by the Rat Flea (*Xenopsylla cheopis*).

Q: A 9-year-old boy presents with a migratory rash with central clearing on the back of his neck. The child had recently been on vacation with his family and had gone hiking. The child's pediatrician observes the rash and suspects an infection with Borrelia burgdorferi. Which of the following is thought to be a virulence factor of this organism?

Expression of outer surface proteins. **Explanation:** The clinical presentation describes **Lyme disease**, caused by the spirochete *Borrelia burgdorferi*. The "migratory rash with central clearing" is the classic **Erythema Chronicum Migrans**, typically transmitted via the bite of the *Ixodes* tick. **1. Why the correct answer is right:** *Borrelia burgdorferi* relies heavily on the differential expression of **Outer Surface Proteins (Osps)** to survive and transition between the tick vector and the mammalian host. * **OspA** is expressed while the bacteria reside in the tick's midgut (helping them adhere to the gut). * **OspC** is upregulated during the tick's blood meal, allowing the bacteria to migrate to the salivary glands and infect the human host. These proteins are essential for immune evasion and tissue attachment, making them primary virulence factors. **2. Why the incorrect options are wrong:** * **Option A & C:** *Borrelia* is primarily an **extracellular** pathogen. It does not typically grow intracellularly in leukocytes or localize in the reticuloendothelial system (unlike *Leishmania* or *Histoplasma*). * **Option D:** Spirochetes like *Borrelia* do not possess classic **LPS (Endotoxin)** found in Gram-negative bacteria. While they have lipoproteins that trigger inflammation, "endotoxin release" is not their characteristic virulence mechanism. **NEET-PG High-Yield Pearls:** * **Vector:** *Ixodes* tick (also transmits Babesia and Anaplasma). * **Reservoir:** White-footed mouse (larvae/nymphs); White-tailed deer (adult ticks). * **Diagnosis:** Clinical (for Erythema Migrans); Serology (ELISA followed by Western Blot) for later stages. * **Treatment:** **Doxycycline** is the drug of choice. Amoxicillin is used in children <8 years or pregnant women. Ceftriaxone is used for neurological or cardiac manifestations.

Q: Rat bite fever may be caused by which of the following organisms?

Streptobacillus moniliformis. **Explanation:** **Rat-bite fever (RBF)** is a systemic zoonotic illness transmitted through the bite or scratch of an infected rodent. It is caused by two distinct bacteria: **Streptobacillus moniliformis** (most common in North America/Europe) and **Spirillum minus** (common in Asia, where it is known as *Sodoku*). 1. **Why Option B is Correct:** * *Streptobacillus moniliformis* is a pleomorphic, Gram-negative, non-motile coccobacillus that grows in chains (streptos = twisted/chain). * **Clinical Presentation:** It typically presents with fever, vomiting, headache, and a characteristic maculopapular rash on the palms and soles, often complicated by migratory polyarthralgia. * **Haverhill Fever:** This is the name given to the illness when *S. moniliformis* is acquired through the ingestion of contaminated milk or water rather than a bite. 2. **Why Other Options are Incorrect:** * **A. Leptospira canicola:** Causes Leptospirosis (Weil’s disease). While transmitted via animal urine (often dogs or rats), it presents with jaundice, renal failure, and conjunctival suffusion, not the classic RBF syndrome. * **C. Borrelia recurrentis:** The causative agent of **Louse-borne Relapsing Fever**, transmitted by the human body louse (*Pediculus humanus corporis*). * **D. Yersinia:** *Yersinia pestis* causes the Plague (transmitted by rat fleas), while *Y. enterocolitica* causes enterocolitis. Neither causes Rat-bite fever. **High-Yield Pearls for NEET-PG:** * **Microscopy:** *S. moniliformis* shows "string of beads" appearance in culture. * **Culture:** It is fastidious and requires blood, serum, or ascitic fluid for growth; it is inhibited by **Sodium Polyanethol Sulfonate (SPS)**, a common anticoagulant in blood culture bottles. * **Differential:** If the question mentions a long incubation period (1–4 weeks) and prominent lymphadenopathy without arthritis, think **Spirillum minus (Sodoku)**.

Question 1

Transovarian transmission is a feature of which disease?

Accepted Answer

Scrub fever

Answer

Epidemic typhus

Answer

Endemic typhus

Answer

Trench fever

Question 2

A patient presents with chills, fever, body rashes, delirium, and subsequent coma, which began shortly after a louse bite. A provisional diagnosis of vasculitis due to rickettsial infection is considered. Which of the following is the most likely causative agent?

Accepted Answer

Rickettsia prowazekii

Answer

Rickettsia typhi

Answer

Rickettsia rickettsiae

Answer

Rickettsia akari

Question 3

A 50-year-old paddy farmer presented to the emergency room in shock. Attendants claim that he had sudden onset of fever with difficulty in breathing about 2 days ago and subsequently also developed hemoptysis. Sputum sample was collected, and Wayson staining was done. The organism isolated was indole positive, methyl red positive, and Voges-Proskauer positive, and fermented glucose, mannitol, and maltose. It also did not hydrolyze urea. Stalactite growth was seen in the ghee broth. What is the drug of choice for the above condition and which vector transmits the disease?

Accepted Answer

Vector: 3 / Drug of choice: Streptomycin

Answer

Vector: 1 / Drug of choice: Streptomycin

Answer

Vector: 3 / Drug of choice: Ampicillin

Answer

Vector: 2 / Drug of choice: Gentamycin

Question 4

Rocky mountain spotted fever is caused by which species of Rickettsia?

Accepted Answer

Rickettsia rickettsii

Answer

Rickettsia typhi

Answer

Rickettsia conorii

Answer

Rickettsia akari

Question 5

Which of the following statements is TRUE?

Accepted Answer

Hantavirus pulmonary syndrome is caused by inhalation of rodent feces.

Answer

Kyasanur Forest Disease (KFD) is caused by the bite of a wild animal.

Answer

Lyssavirus is transmitted by ticks.

Answer

Yellow fever is transmitted by Anopheles mosquito.

Question 6

Which of the following is NOT true regarding Chlamydia psittaci?

Accepted Answer

It causes non-gonococcal urethritis.

Answer

It is endemic in birds.

Answer

It can be grown in a specified laboratory medium.

Answer

Tetracycline is the treatment of choice.

Question 7

Which of the following species of Brucella tends to produce a more acute and aggressive presentation?

Accepted Answer

B. melitensis

Answer

B. suis

Answer

B. abortus

Answer

B. canis

Question 8

Stalactite growth in ghee broth is due to?

Accepted Answer

Yersinia pestis

Answer

Haemophilus influenzae

Answer

Corynebacterium diphtheriae

Answer

Treponema pallidum

Question 9

A 9-year-old boy presents with a migratory rash with central clearing on the back of his neck. The child had recently been on vacation with his family and had gone hiking. The child's pediatrician observes the rash and suspects an infection with Borrelia burgdorferi. Which of the following is thought to be a virulence factor of this organism?

Accepted Answer

Expression of outer surface proteins

Answer

Intracellular growth in leukocytes

Answer

Localization in reticuloendothelial cells

Answer

Endotoxin release

Question 10

Rat bite fever may be caused by which of the following organisms?

Accepted Answer

Streptobacillus moniliformis

Answer

Leptospira canicola

Answer

Borrelia recurrentis

Answer

Yersinia

Zoonotic Diseases — MCQs

Zoonotic Diseases — MCQs

On this page

Practice by Chapter

Want unlimited practice?