Posts Tagged ‘infectious disease’
By: Ashley Parker, Ph.D.
Tuberculosis (TB) is a disease transmitted via droplets from the throat and lungs of infected individuals, and is caused mainly by the bacterium Mycobacterium tuberculosis. According to the 2015 Global TB report published by the World Health Organization (WHO), TB affects millions of people every year and ranks alongside the human immunodeficiency virus (HIV) as the leading cause of death worldwide; in addition, 9.6 million new cases of TB were estimated in 2014. We typically think of TB as a disease that is spread from person-to-person; however Meera Senthilingam, writer for CNN, recently published an article about the transmission of TB from infected animals to humans, highlighting the spread of tuberculosis via a contaminated food source that originated in a cow infected with Mycobacterium bovis.
Although M. bovis causes less than 2% of the total number of TB cases in the United States (less than 230 cases per year), according to the Centers for Disease Control and Prevention (CDC), the organism is also found in cattle and other animals such as bison, elk, and deer. “An increase in the number of cattle-associated cases in the U.S. was found to be near the Mexico border and among the Hispanic communities,” and was reported to be associated with the ingestion of unpasteurized milk and dairy products such as raw cheese, according to a speaker at the 46th World Conference on Lung Health. In California, the incidence of tuberculosis caused by M. bovis has increased recently. Of the approximately 19,000 patients who were enrolled in the states’ tuberculosis registry between 2003 and 2011, 3.4% of 2,384 cases were infected with M. bovis in 2003, increasing to 5.4% of 1,808 cases in 2011, with six cases having an association with at least one parent or guardian born in Mexico (Gallivan M, et al.). In an effort to manage the incidence and spread of bovine TB, the state of California is implementing strategies to limit the demand and distribution of unpasteurized milk and dairy products.
In other countries such as the United Kingdom, bovine TB is a major challenge for cattle farming industries, particularly in the west and southwest regions of England. In an effort to eradicate bovine TB, the UK government has developed actions outlined in their Bovine TB Strategy for England and UK Bovine TB Eradication Program, which include testing cattle herds for bovine TB and controlling TB in herds when detected, controlling the disease in badgers, improving biosecurity and husbandry on farms, developing TB vaccines for cattle, vaccinating badgers against TB, helping other industry sectors to deal with TB in non-bovine species, and developing the comprehensive bovine TB research program. According to a report by the CDC, many countries, particularly developing countries with limited resources, lack the ability to report all TB cases because of the difficulties with identifying suspected cases and establishing a diagnosis, and issues with recording and reporting cases. Another study presented at the 46th Union World Conference on Lung Health suggested that improper diagnosis and inadequate treatment was occurring in developing regions. In this study, “3,595 cattle and 266 livestock workers in Nigeria were screened for bovine TB; 10.4% of individual cattle, 42.9% of herds, 4.6% of butchers, and 6.1% of marketers were positive for tuberculosis.” There were major concerns about bacterial resistance, considering M. bovis is naturally resistant to pyrazinamide, a first line drug used as a standard treatment. Unfortunately, the CDC reports, of the 55 African countries, only 7 apply disease control measures as part of a test-and-slaughter policy and consider bovine TB to be a notifiable disease, while the remaining 48 apply inadequate control strategies or fail to control the disease. This leaves 85% of cattle and 82% of the human population exposed to bovine TB that is inadequately controlled or not controlled at all. In general, evaluation of M. bovis is not a routine part of laboratory testing for tuberculosis complex isolates, therefore most patients with the disease are not recognized. According to an article by Elizabeth Talbot, MD, the initial diagnostic approach for M. tuberculosis is also standard for M. bovis, including acid-fast staining, mycobacterial culture of relevant specimens, molecular testing for mycobacterial DNA, tuberculin skin test, and interferon gamma release assays. However additional tests should be requested in settings where M. bovis has high incidence rates or may be suspected, in an effort to properly identify the species. These tests include susceptibility testing, biochemical assays, and genomic analysis.
The spread of human M. bovis is a recognizable public health issue that is capturing attention in the United States and abroad. Although this organism primarily poses challenges in developing countries, the WHO recognized the importance and potential threat of human M. bovis in 1950 in the report of the Expert Committee on Tuberculosis. Recently, collaborative efforts have been made to eliminate bovine TB, involving WHO’s Division of Emerging and other Communicable Diseases Surveillance and Control, Veterinary Public Health program of the WHO Regional Office for the Americas, Pan American Health Organization, and additional working groups including the Food and Agriculture Organization of the United Nations, Office International des Epizooties Consultation on Animal Tuberculosis Vaccines. Successful vaccinations for cattle (developed in 1998 by WHO and organizations listed above) are currently being used in some countries. Plans to eradicate the disease are underway in specific countries, and are also part of a global 10-year plan, but will require better epidemiological surveillance to identify high risk areas, and properly implement control and elimination programs. Also, educating and notifying the public about the potential risk factors will help in the prevention of bovine TB.
By: Amy Kullas, PhD
On June 29 of this year, the California Senate passed SB277, one of the nation’s strictest vaccination laws. The very next day, California’s governor, Edmund Brown, Jr., signed the bill into law. SB277 transforms California – previously one of the most liberal states in terms of vaccination requirements – into one of the strictest. This bill makes California the third state (after Mississippi and West Virginia) to eliminate religious and other personal exemptions for vaccination. Under the bill, unvaccinated children without a medical exemption would have to study at home or in organized, private home-schooling groups rather than attend public school. Beginning January 1, 2016, schools will begin verifying that children entering kindergarten or advancing to seventh grade for the upcoming school year are vaccinated. On and after July 1, 2016, in order to attend public or private schools, students will need to have received vaccines for: diphtheria, Haemophilus influenza type b (Hib meningitis), measles, mumps, pertussis (whooping cough), poliomyelitis, rubella (German measles), tetanus, hepatitis B and varicella (chickenpox).
Infectious diseases are not new and have been killing since the dawn of mankind. However, in the 18th century, a revolutionary scientific innovation was identified: vaccination. Edward Jenner is accepted as the ‘grandfather’ of the modern vaccine. After hearing stories of how dairymaids were seemingly naturally protected from smallpox after having suffered from cowpox, he hypothesized that cowpox could be used as a deliberate mechanism of protection. In May of 1796, Jenner located a dairymaid, who had fresh lesions on her hands and arms and inoculated a young boy with material drawn from one of her pustules. The boy reportedly developed mild symptoms, but after about 10 days felt much better. That July, Jenner inoculated that same boy again, this time with pustules from a fresh smallpox lesion. After no disease development, Jenner concluded that the boy was protected from smallpox based on his earlier exposure to cowpox. This groundbreaking discovery of transmitted protection was the start the concept of immunization.
The controversy around eliminating the “personal belief exemption” was ignited in California after a measles outbreak started in at Disneyland last December and quickly spread to seven states and internationally into Canada and Mexico. Though the outbreak sickened approximately 150 people in the United States, fortunately no deaths were reported. The majority of the individuals infected by the measles outbreak were either unvaccinated (71 or 45%) or their vaccination status was unknown (60 or 38%). Only 28 people or a dismal 18% had reported receiving the measles vaccine! Further, of the U.S. residents who caught measles and were unvaccinated, 29 (43%) gave philosophical or religious objections to vaccination while 27 (40%) were ineligible because they were too young to receive the full course of vaccines, or they had a medical condition that prevented vaccination. Amidst the measles outbreak, Californian senators, Barbara Boxer and Dianne Feinstein wrote to state health officials, saying that “while a small number of children cannot be vaccinated due to an underlying medical condition, we believe there should be no such thing as a philosophical or personal belief exemption, since everyone uses public spaces…. As we have learned in the past month, parents who refuse to vaccinate their children not only put their own family at risk, but they also endanger other families who choose to vaccinate.”
Dr. Annie Sparrow, Deputy Director Human Rights and Assistant Professor of Global Health at Icahn School of Medicine at Mount Sinai in New York, highlighted another important consequence of infectious diseases making a global comeback: “measles, long forgotten, is ‘back’ in the United States and far too few doctors know how to recognize it.” Alarmingly, if people go to their doctor or to the hospital when they’re feeling sick and a diagnosis at that early stage is missed, the number of people potentially exposed to the disease could increase exponentially. Many early symptoms of diseases often present themselves in similarly with fever, rash, or both, making a diagnosis difficult. Doctors may also no longer consider some of the formerly common childhood diseases, since they have been generally accepted as eradicated due to vaccine development, and this unintentional oversight could have grave public health consequences.
Vaccination is an extremely effective strategy for preventing infectious diseases. However, this strategy is only successful when the vast majority of individuals are immunized against a particular pathogen in order to offer some protection to individuals who are not medically able to receive the vaccine. When a high percentage of the population is vaccinated, it becomes more difficult for the infectious diseases to spread because there are so few people who could potentially be infected in a concept called community immunity or herd immunity. The people who are unable to get vaccinated for medical reasons include infants, pregnant women, and immunocompromised individuals. But for those individuals who are healthy enough to get vaccines, but choose not to, why don’t they vaccinate?
The misguided “anti-vaccination movement” began with a paper published by Andrew Wakefield in The Lancet in 1998. The impact of this now-retracted paper still ripples through the scientific community and beyond, to within the general public in the United States. In the paper, the authors alleged that eight children (out of a very small sample size of 12) developed autism and bowel disease shortly after receiving the measles, mumps and rubella (MMR) vaccine. However, the MMR vaccine had been widely used since 1968, which begs the question of why would it take 30 years for this ‘association’ to be made? After numerous researchers continually failed to replicate Dr. Wakefield’s results, the scientific community uncovered that it was a fraudulent study. However, it still took over 10 years for the retraction to be published. Wakefield has since lost his medical license and in 2010 wrote a book disputing the charges against him. He has been described as the “father of anti-vaccine movement.” Because Dr. Wakefield’s fraudulent conclusions continue to be perpetuated by some, the medical community, scientists, and lawmakers must take a united stance to correct the damage done by one paper.
By signing SB277, the Californian government has mandated vaccinations for all school-aged children regardless of their parents’ personal or religious beliefs. Kudos to California, West Virginia, and Mississippi for passing such strict vaccination laws! My hope is that the other 47 states and the District of Columbia will follow suit for the good of us all.