What are the other Names for this Condition? (Also known as/Synonyms)

• Human Ehrlichial Infection, Sennetsu Type
• Neorickettsia Sennetsu Infection
• Sennetsu Neorickettsiosis

What is Sennetsu Fever? (Definition/Background Information)

• Neorickettsia sennetsu, a bacterium belonging to the Anaplasmataceae family, causes Sennetsu Fever in humans. This infection is classified under the category ‘ehrlichiosis’
• Sennetsu Fever is a rare and non-contagious infection that is endemic to some southeast Asian countries. The exact prevalence of Sennetsu Fever is not known; however, individuals of all ages may be affected
• Certain types of fish have been identified as the vector of Neorickettsia Sennetsu bacterium. In the endemic regions, eating raw, undercooked, or fermented fish is common; thus, allowing the bacteria to infect humans
• Once in the body, the bacteria enter the bloodstream and invade the lymphatic system and certain white blood cells (particularly the macrophages and monocytes). The bacteria live inside these specialized immune cells and may cause a decrease in the number of white blood cells. 
• Notwithstanding the above, an inflammatory response may be elicited in the liver in response to the infection, causing abnormalities in liver enzymes
• A sudden onset of high fever, muscle aches, headache, nausea, vomiting, enlarged liver and spleen are some known symptoms of Sennetsu Fever. The symptoms may begin about 1-2 weeks after consuming infected fish
• A diagnosis of the condition is undertaken based on a physical examination, presenting symptoms, and an understanding of the individual’s eating habits. Blood tests, to check for white blood cell numbers, and a polymerase chain reaction (PCR) test to confirm the infection are usually performed
• Typically, the treatment for this bacterial infection is using antibiotics belonging to the tetracycline family. The duration of treatment of Sennetsu Fever may be determined by the severity of symptoms
• Sennetsu Fever can be prevented by abstaining from eating raw, undercooked, or fermented fish. The prognosis for the infection is good with prompt treatment, provided the affected individual is generally healthy

Who gets Sennetsu Fever? (Age and Sex Distribution)

• Sennetsu Fever is reported in some southeast Asian countries, where fish is a staple food, and eating raw fish is common. Such countries include Japan, Laos, Philippines, and Thailand
• Males and females of all ages may be infected with the bacterium causing the infection

What are the Risk Factors for Sennetsu Fever? (Predisposing Factors)

• The primary risk factor for developing Sennetsu Fever is eating raw, undercooked, or fermented fish
• Individuals who have reduced immunity (such as those with HIV infection, on cancer treatment, transplant patients on immune-suppressor drugs, etc.) may be more susceptible to Sennetsu Fever after consumption of undercooked fish 

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Sennetsu Fever? (Etiology)

Sennetsu Fever is caused by infection of Neorickettsia sennetsu bacterium. The following sequence of events is known to cause infections in humans:

• The bacteria infect a type of flatworms called flukes
• The fish carry the pathogenic bacteria, as the flukes are parasitic in fish
• When humans consume such fish without properly cooking it to eliminate the bacteria (and flatworms), they are infected
• The bacteria enter the bloodstream, and subsequently, the lymphatic system. The lymphatic system transports white blood cells throughout the body. The white blood cells are the ‘soldiers’ of the body, and they fight any infections
• In humans, Neorickettsia sennetsu specifically targets monocytes and macrophages, which are specialized white blood cells involved in destroying invading microbes
• The invasion of the white blood cells by these pathogenic bacteria may lead to a reduction in the numbers of white blood cells (known as leukopenia)
• Additionally, the bacteria may grow in membrane-bound cavities inside organs and tissues, such as bone marrow, lymph nodes, liver, spleen, kidneys, lungs, and the cerebrospinal fluid

Sennetsu Fever is not contagious; it does not spread from one individual to another.

What are the Signs and Symptoms of Sennetsu Fever?

The symptoms of Sennetsu Fever may begin approximately 1-2 weeks after infection, and may vary in type and severity among individuals. The common signs and symptoms include:

• Sudden onset of high fever, chills
• Sore throat (pharyngitis)
• Swollen lymph nodes
• Severe headaches
• Muscle pain, joint pain
• Nausea and vomiting
• Lack of appetite
• Enlarged liver and spleen (hepatosplenomegaly)

How is Sennetsu Fever Diagnosed?

The diagnosis of Sennetsu Fever is made using the following tools:

• Complete physical examination and assessment of symptoms
• Seeking information about the affected individual’s food habits (whether he/she has consumed uncooked or under-prepared fish), travel history, and if he/she has visited any southeast Asian countries
• Blood tests to evaluate blood cell count
• Liver function tests: An inflammatory response in liver cells is observed in Sennetsu Fever, with an increase in the enzyme known as hepatic transaminase is noted
• Polymerase chain reaction (PCR) test to identify and confirm Neorickettsia sennetsu 

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Sennetsu Fever?

Some potential complications of Sennetsu Fever may include: 

• Prolonged illness
• Problems with the function of liver
• Meningitis
• Possibility of repeat infections: It has been reported that antibodies to the bacterium are not found in an individual’s system when checked 44 months after acute illness following infection. This would make the individual prone to more episodes of Sennetsu Fever, since contracting the infection once, does not appear to render the individual resistant to the causative bacterium

How is Sennetsu Fever Treated?

The treatment for Sennetsu Fever may be commenced before the blood test results are procured, if a healthcare provider suspects Neorickettsia sennetsu infection.

• Typically, the tetracycline class of antibiotics (such as doxycycline, minocycline) is used to treat this condition. In severe cases, an affected individual may need hospitalization
• Infected pregnant women may be prescribed a different antibiotic, since the tetracycline family of antibiotics may be harmful to the fetus

How can Sennetsu Fever be Prevented?

It is possible to prevent Sennetsu Fever by ensuring the following steps:

• Not consuming raw, undercooked, or fermented fish in regions of the world (southeast Asian) where the condition is endemic
• Being aware of potential illnesses/infections in the region of the world one is planning to visit

What is the Prognosis of Sennetsu Fever? (Outcomes/Resolutions)

• The prognosis of Sennetsu Fever is determined by the overall health of the affected individual, and prompt treatment upon diagnosis
• If the individual is healthy and treatment is promptly provided, the outcome is favorable
• However, a lack of treatment can result in complications, prolonging the recovery process and necessitating hospitalization

Additional and Relevant Useful Information for Sennetsu Fever:

• Babesiosis is a rare and severe tick-borne disease, caused by a parasite. The ticks (blacklegged ticks, deer ticks, or bear ticks) are carriers to parasites of the genus babesia

The following link may help you find useful additional information on babesiosis:

http://www.dovemed.com/diseases-conditions/babesiosis/