Bacteria, Viruses and Health
A 38 year old man named Brian visited his local doctor complaining of high fever, malaise, loss of appetite and headache. Patient history revealed that Brian is a photojournalist for a travel magazine. In the past 30 days Brian has traveled on assignment to Italy, London, and France. Brian is very careful not to drink local water when traveling and he only eats well cooked foods. He did mention being bit by a ferret on the street of France, but the animal seemed fine and the owner took it away after the incident. Brian did not seek medical care because he thought it would be too complicated to deal with while overseas and the bite was very small. He does have pain and itching at the site of the animal bite. Lab tests on Brian’s blood did not show the presence of any gram-positive or gram-negative bacteria.
1. What microorganism do you believe is to blame for this illness (be specific)? Provide background information on this organism, history, morphology, virulence factors, toxins, etc.
I believe that Lyssavirus rabies is responsible for Brian’s illness. The rabies virus is neurotropic and is part of the rhabdovidae family and small mammals are especially susceptible to this disease but it can be transmitted to any mammal including humans. “Rabies has been noted in history since about 2000 BC when owners of rabid dogs were cautioned against getting bitten. The word rabies is derived from the Latin word rabies, which meant ‘madness or rage.’ In the 15th century, Italian physician Girolamo Fracastoro studied rabies and concluded that it was a communicable disease transmitted to people by direct contact with saliva from infected animals. He termed the disease “rabies.” In 1895, after studying the data presented by Fracastoro centuries before, Louis Pasteur was able to produce a vaccine against the disease-causing viruses without actually discovering or isolating the viruses. The virus that causes rabies is Lyssavirus (Lyssa is the Greek goddess of madness, rage, and frenzy) rabies, a cylindrical or bullet-shaped virus that is enveloped and contains a negative-sensed RNA that makes up its genetic material.” (MedicineNet, 2012)
This transmission electron micrograph reveals the bullet-shaped morphology of the rabies virus. Courtesy of: http://www.ppdictionary.com/viruses/rabies.htm
2. What information from the patient’s symptoms contributed to your decision? Did this information allow you to rule out any other possible culprits? What information from the patient’s history and/or lab samples that contributed to your decision? Support your answers with factual evidence and logical reasoning.
Brian’s symptoms consisted of a high fever, malaise, loss of appetite and a headache which are consistent with a systemic infection of some etiology. Brian’s bite wound itself had localized inflammation since itching and pain were associated with it. Considering the patient’s history, it is unlikely that his symptoms are due to fungal, prionic, or parasitic infection(s) but are not entirely ruled out due to his recent travels and potential exposure to pathogens of this nature despite his diligence to avoid exposure. Brian’s blood cultures showed that there was no Gram positive or Gram negative bacteria at the site of the bite wound which was indicative that bacteria was not responsible for his symptoms. The next logical option was that his infection was viral in nature. Given the type of animal the bite was received from, and their susceptibility as carriers of disease, the etiology of Brian’s infection can most likely be traced back to the ferret he came in contact with. Ferret saliva can carry both bacteria and viruses making it capable of transmitting a potential pathogen if the integrity of the skin is compromised. Furthermore, itching and pain at the wound site, fever, and headache are all classic symptoms of the early stage of rabies in humans. “After the first exposure (in most people, an animal bite), the symptoms of itching or discomfort like pins or needles pricking the skin occur at the bite area. In addition, the person may develop fever and a headache. Investigators suggest these symptoms may last from about two days to weeks. This is the acute phase or the acute incubation phase of the disease.” (MedicineNet, 2012) In addition to this evidence, Brian’s infection is consistent with the known timeline of exposure to the development of symptoms in humans. According to the history given, it is unclear whether the ferret was quarantined or experienced latent neurological stages of the illness which ultimately resulted in death. It is unclear if public health officials in France have been made aware of the incident so it is assumed that the animal is not available for necropsy and thus cannot contribute to any diagnostic decisions.
3. What is the epidemiology of this disease? Identify risk factors for this disease and describe the disease course/outcome in humans.
Ferrets are capable of contracting the raccoon and skunk strains of the virus in the U.S. and the fox strain in Europe. Despite their propensity to contract and transmit diseases, it is highly unusual that a ferret would infect a human with rabies through a bite exposure but it is not impossible or absolutely unheard of. Cats, dogs and livestock represent the largest rabies risks to humans due to our close contact with them. Also, there is a low incidence of rabies vaccinations for domestic animals in many countries making it endemic in parts of the world. Bats, skunks, foxes and raccoons represent the largest rabies risks in the wild but again, the virus can be transmitted to any mammal. There are two ways to contract rabies, bite and non-bite exposures with an infected mammal. “Exposure requires that there be infective virus and penetration of the virus into wounds or mucous membranes. Non-bite exposures include scratches, licks, inhalation of aerosols and other events that lead to contamination of an open wound or mucous membrane.” (Rabies and the Domestic Ferret, 2009) The fact that the owner of the ferret that bit Brian took the animal away after the incident could be attributed to the owner’s knowledge that the ferret was not immunized. Most responsible ferret owners are aware of the potential risks that ferrets can pose and that euthanasia can sometimes be the result of a bite investigation if a ferret is not vaccinated for rabies. Most likely the owner was aware of this and to avoid any trouble he took the ferret away. It’s also possible that the owner noticed that the ferret had been acting strangely and realized that the ferret may have contracted rabies after the bite occurred and took him away to avoid trouble.
4. What steps can be taken to treat the illness? How and why are the treatments effective (or ineffective)? Are there any concerns or other complications of this disease?
Due to Brian’s exposure, symptoms and the lack of knowledge regarding the state of the ferret, cleansing of the wound and immediate preemptive treatment with rabies immune globulin and a rabies vaccine schedule should be administered to avoid late stage neurologic involvement while laboratory RT-PCR tests confirm this diagnosis through the detection of rabies antibodies in Brian’s blood. “As of 2010, the CDC recommends additional doses (injections) of rabies vaccine [Imrab 3] on the third, seventh, and 14th day after exposure. This schedule is for people who have had no previous treatment (vaccination) against rabies. For people previously vaccinated against rabies, only two doses of the vaccine are recommended; one as soon as possible after the exposure (no rabies immune globulin is recommended) and one more three days later. The reason human rabies immune globulin is used (and sometimes even injected into the bite area) is that it immediately attacks the virus and slows or stops viral progression through the nerves. [The rabies] vaccine is used to stimulate the body’s immune response enough to make the body develop enough of an immune response to eventually kill all of the virus population in the body.” (MedicineNet, 2012) Brian should be continually monitored for anxiety, stress, tension, delirium, drooling, convulsions, exaggerated sensation at the bite site, excitability or combativeness, hallucinations, loss of feeling in an area of the body, loss of muscle function, muscle spasms, numbness and tingling, restlessness, insomnia, and difficulty swallowing as these are indicative of the progression of neurological involvement and thus the latent stages of illness which will require more intensive supportive care and may lead to death. Containment and quarantine are only necessary in late stage human cases where the infected individual is a danger to themselves and/or their caregivers and require substantial supportive care and additional infection control standards. Human-to-human transmission of rabies is rare and mostly occurs through organ transplantation. The prognosis for patients who receive immediate treatment is extremely good. However, death is usually imminent for patients who display the latent stages of illness.
Management of Bites to Humans, Animal Bites and Rabies Risk - Minnesota Dept. of Health. (n.d.). Minnesota Department of Health. Retrieved March 20, 2012, from http://www.health.state.mn.us/divs/idepc/diseases/rabies/risk/human.html
Rabies. (n.d.). MedicineNet. Retrieved March 20, 2012, from www.medicinenet.com/rabies/article.htm
Rabies and the Domestic Ferret. (n.d.). Kansas State University. Retrieved March 20, 2012, from www-personal.ksu.edu/~sprite/RABIES.HTML
Table 1: Human Rabies Risk Evaluation: Species of the Biting Animal. (n.d.). Minnesota Department of Health. Retrieved March 20, 2012, from www.health.state.mn.us/divs/idepc/diseases/rabies/risk/table1.pdf
Woerpel, R., & Rosskopf, W. (n.d.). Ferret Facts . Animal Health Center . Retrieved March 20, 2012, from http://www.caringtogether.com/exotics/ferrets.html