Q Fever

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Q Fever

Introduction

Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

BIBLIOGRAPHY

Introduction

Q fever is a disease of humans and some animals that is caused by a bacterium called Coxiella burnetii. The infection is a zoonosis—it is passed to humans by contact with infected animals that are not usually harmed by the organism. The animals typically affected are sheep, cattle, and goats. Q fever can occur and clear quickly (this type is called an acute infection), or can persist for a much longer time (this is called a chronic infection).

WORDS TO KNOW

ACUTE: An acute infection is one of rapid onset and of short duration, which either resolves or becomes chronic.

GRAM-NEGATIVE BACTERIA: All types of bacteria identified and classified as a group that does not retain crystal-violet dye during Gram's method of staining.

ZOONOSES: Zoonoses are diseases of microbiological origin that can be transmitted from animals to people. The causes of the diseases can be bacteria, viruses, parasites, and fungi.

Disease History, Characteristics, and Transmission

Q fever was first described in Australia in 1935 by the physician Edward H. Derrick (1898–1976) in people working in an Australian slaughterhouse. At the time, the cause for the illnesses was unknown; hence the term Q, which was short for Query. In 1937, C. burnetii was isolated and identified. The following year, the same organism was isolated from ticks in Montana, leading researchers to suspect a tick-mediated animal-human connection. The U.S. researchers also showed that the microbe was a type of bacterium called a rickettsia. Rickettsia are important from the standpoint of infectious diseases. As an example, other rickettsia are responsible for the potentially serious diseases called Rocky Mountain spotted fever and trench fever.

C. burnetti is a gram-negative organism, meaning it has two membranes surrounding the inner contents of the cell. In addition, the bacterium requires a host cell in order to grow and divide. This is similar to viruses. However, unlike viruses, which are not considered to be alive, C. burnetii is living and can survive, but cannot grow and divide, when not in a host cell.

The bacteria can survive for a long time in the natural environment, as they are not easily killed by heat, dryness, and even chemical compounds that readily kill other bacteria. This makes it more likely that the bacteria will be spread to those who come into contact with them.

Q fever results from inhalation of the bacteria. Infections have been traced to the inhalation of bacteria dislodged into the air from dry hay or a dusty barnyard. Only a few living organisms need be inhaled to establish an infection. This route of infection is different from other rickettsial diseases, where the bacteria are transferred from animal to human by tick bites. People who are most a trisk of acquiring Q fever are those who are around animals like goats, sheep, and cattle, since these animals can naturally harbor the bacterium. The bacteria can be present in the milk, urine, amnioticfluid, and feces of the animals. Also, bacteria canbe present in amniotic fluid and the placenta, and so can be spread to people who help in the birth of animals. Veterinarians, processing plant workers, and livestock farmers are more susceptible to Q fever than the general population.

For reasons that are not clear, only about 50% of those people who inhale the bacteria display symptoms. The symptoms include a sudden and high fever, a flulike sickness, severe headache, nausea with vomiting, abdominal pain, and a general feeling of being unwell. People can lose weight during their illness, which can take some time to regain following their recovery. Only 1–2% of those with the milder form of Q fever die of the illness.

A serious lung infection (pneumonia) can develop in 30–50% of people with Q fever. Liver damage including hepatitis can also occur. These symptoms usually ease in several months. However, a more persistent form of Q fever can develop, resulting in debilitating damage to heart valves due to the longer-lasting infection that kills up to 60% of those who acquire the chronic infection.

There are two different forms of C. burnetii that differ in the types of molecules present on the outer surfaces of their cells. The two forms have been designated phase I and phase II. The phase I form is associated with the chronic form of Q fever.

The short-term form of Q fever does not always immediately lead to the longer form; indeed, the chronic form of Q fever can develop in the absence of the milder form of the disease. The time lag between the short-term and chronic forms of Q fever can be as long as several decades.

Scope and Distribution

The bacterium responsible for Q fever occurs worldwide. Countries such as Australia and the United States with a heavier emphasis on livestock agriculture, or which have a greater prevalence of animals that naturally harbor the bacterium, have a higher occurrence of the disease.

Treatment and Prevention

Diagnosis of Q fever most typically involves the detection of antibodies to C. burnetii or genetic material from the bacterium. Growing the organism is difficult, so detection of the bacterium itself is not typically accomplished. Following diagnosis, treatment consists of antibiotic therapy. Typically, this is effective, although the therapy will be necessary for years when the infection is chronic. Heart valve damage can require replacement of the defective tissue.

A vaccine for Q fever exists. As of 2007, it is available in Australia and parts of Europe, but is not yet widely available in North America. Beginning in 2001, people at risk in Australia could be vaccinated. North Americans identified at higher risk of Q fever can also now be vaccinated. Similarly, a vaccine for animals exists, but is not yet in widespread use in North America.

Prevention of the transmission of the bacterium to humans involves wearing masks when around domestic livestock and the prompt disposal of the placenta and other tissues resulting from the birth process.

IN CONTEXT: SOCIAL AND PERSONAL RESPONSIBILITY

The Division of Viral and Rickettsial Diseases at the Centers for Disease Control and Prevention (CDC) states that the following measures should be used in the prevention and control of Q fever:

Educate the public on sources of infection.
Appropriately dispose of placenta, birth products, fetal membranes, and aborted fetuses at facilities housing sheep and goats.
Restrict access to barns and laboratories used in housing potentially infected animals.
Use only pasteurized milk and milk products.
Use appropriate procedures for bagging, autoclaving, and washing of laboratory clothing.
Vaccinate (where possible) individuals engaged in research with pregnant sheep or live C. burnetii.
Quarantine imported animals.
Ensure that holding facilities for sheep should be located away from populated areas. Animals should be routinely tested for antibodies to C. burnetii, and measures should be implemented to prevent airflow to other occupied areas.
Counsel persons at highest risk for developing chronic Q fever, especially persons with pre-existing cardiac valvular disease or individuals with vascular grafts.

SOURCE: Centers for Disease Control and Prevention, National Center for Infectious Diseases, Division of Viral and Rickettsial Diseases

Impacts and Issues

Q fever can be a potentially serious disease because it can be spread from animals to people. In the United States, cases of the illness have been required to be reported to the Centers for Disease Control and Prevention since 1999. Imported livestock are also monitored for the presence of the bacterium, since transfer to other domestic animals could occur unknowingly in the absence of development of any symptoms in these hosts.

Why only about 50% of infected people display symptoms of infection is still unclear, but is important to learn if vaccines are to be fully protective. Research is underway to try and distinguish factors associated with people, the bacterium, or both that help some people ward off the consequences of infection. Additionally, it is not clear why Q fever does not persist for a long time in some people, but becomes a chronic, destructive, and potentially life-threatening condition in others.