Scrub Typhus - Causative Agent, Symptoms,Treatment and Prevention

Scrub Typhus/ Typhus Fever

Scrub typhus, also known as bush typhus, is a mite-borne disease caused by bacteria Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi).  Scrub typhus infection is spread to people through bites of infected chiggers or larval mites.

Scrub typhus is the most common disease among rickettisial disease in man, known as tsutsugamushi diseases. It has been derived from japanese word.

 

Tsutsuga – meaning something small and dangerous; illness

Mushi - meaning creature; insect

 

Human get Scrub typhus infection through bites of infected chiggers (larval mites). The symptoms of scrub typhus are fever, headache, body aches, lesion at bite site , macular rash rash lymphadenopathy

Epidemiological Triad

Agent – The causative agent of scrub typhus is rickettisia (Orientia  tsutsugamushi ); Gram-negative bacterium , belongs to rickettsiaceae family.

 

Host – Human accidently get infected. Rickettisia tsutsugamushi servive in mites (larval mites). Chiggers are both reservoir and vector  for Orientia tsutsugamushi that belongs to leptotrombidium akamushi and  leptotrombidium deliense.

 

Environment – Rainy season

 

 

 

How Human get Infected?

 

Orientia  tsutsugamushi found in harbour (part of a body of water) areas where heavy scrub vegetation's occur and chiggers get infected .

Orientia tsutsugamushi is spread by trombiculid mite larvae (chiggers). scrub typhus Infection high during wet season when the mites lay their eggs, the larva (chigger) that feeds on rural rodents, including rats, field mice.

Human get accidentally get infected by chigger bite or When travelling scrub typhus infected areas.

 

 

Mode of Transmission 

 

Transmitted by bites of infected larval mites (chiggers).

 

 

Causes of Scrub Typhus

 

Scrub typhus is spread by bite of chiggers (infected larval mites) which are found in areas of heavy scrub vegetation.

After an incubation period of  5 - 20 days (10-12 days) , symptoms of scrub typhus start suddenly and include fever, chills, headache,  body ach,  lymphadenopathy. At onset of fever, an eschar  developed at the site of the chigger bite.

Scrub typhus Eschar Formation

 

After the bite of chigger mite, at bite site of skin develop Eschar.  Eschar is a painless, necrotic lesion Escher (piece of dead tissue)  of the skin at the site of a bit. At begins appear red that vesiculates and ruptures and form dark region at the site of the chigger bite, called eschar.

 

 

Incubation period

 

The incubation period of scrub typhus is about 5 to 20 days (10-12 days) after the initial bite of chigger.

 

Clinical Manifestation

                                                                                     

Symptoms of scrub typhus usually begin within 10 days of being bitten by infected chiggers. Signs and symptoms include:

1. Fever 104-105 degree F with chills,

2. Cough

3. Malaise

4. Headache,

5. Conjunctiva irritation- Infection of mucus membrane lining of eye

6. Eschar at site of chigger bite – Formed wound at site of chiggar bite

7. Maculopapular rash

8. Myalgia - Body aches and pain in a muscle

9. Lymphadenopathy - Enlargement of lymph nodes

 10. Prostration - state of extreme physical exhaustion

 

In severe case

 

1. Increased pulse rate

2. Decreased blood pressure

3. Loss of consciousness - Mental changes, ranging from confusion to coma

4. Spleenomegaly - Enlargement of spleen

5. Twitching of muscles

6. Interstitial myocarditis

7.Interstitial pneumonitis

8. Lymphocytosis

9. Encephalitis,

10. Respiratory failure

11. Circulatory failure/organ failure

 

 

Pathophysiology of Scrub Typhus

 

1. Humans get infected by Chigger bite

2. Bacteria multiply in inoculation site and lead papule, ulcer, necrosis of skin and formed cause Eschar

3. Bacteria attach to endothelial cells lead to  vasculitis

4. Bacteria spread into the lymph node and replication in lymph nodes cause lymphadenopathy

5. Lead to enlargement  of liver and spleen

 

Laboratory Diagnosis

 

1. Detection of specific antibodies against scrub typhus in blood

2. Isolation of Rickettsiae from blood or other body tissues

3. Complement fixation test

4. Weil-felix test

5. Elisa test

6. Indirect immmunofluorescence assay

6. PCR for orientia tsutugamushi

 

 

Treatment of Scrub Typhus

 

No vaccine is available to prevent scrub typhus infection . To prevent and reduce the risk of scrub typhus infection by avoiding contact with infected chiggers. 

Scrub typhus cases should be treated with the antibiotic Doxycycline, Tetracycline, chloramphenicol

Antibiotics are most effective to treat infection.

Drug of choice –Tetracycline

Azithromycin drug is used in resistance cases of Scrub typhus.

 

Prevention and Control

 

1. Diagnosis and treatment

2. Use of insect repellents - used to prevent the chigger bite.

3. Environmental sanitation  - control the vector of scrub typhus and break the cycle of transmission of scrub typhus.

4. Prophylactic treatment - Single dose of chloramphenicol or tetracycline administered.

5. Wear Protective clothing

6. Avoid travelling those areas, where lots of vegetation and brush where chiggers may be found.

Murine Typhus is also rickettsial disease, know the mode of transmission of Murine typhus.