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Rare zoonotic diseases

Lesser-known illnesses

Introduction


From COVID-19 possibly coming from livestock in Wuhan market to HIV resulting from numerous transmissions between African primates, it seems that zoonotic diseases are difficult to control. They occur when pathogenic microorganisms are spread from animals to humans or vice-versa. Their impact on human civilization is alarming because they are responsible for 2.5 billion cases of illness and 2.7 million deaths in humans annually around the world. Although there is a lot of information regarding more familiar zoonotic diseases such as rabies and malaria, this article focuses on those that may be less discussed as they could become more problematic in the future.


Crimean-Congo haemorrhagic fever (virus)


To begin, Crimean-Congo haemorrhagic fever (CCHF) is a viral disease, which spreads when humans are bitten by ticks carrying the virus along with farmers killing infected livestock. It is endemic in more than 30 European, African and Asian countries with the exact factors contributing to the increased cases of CCHF being a mystery. 


Diagnosing the disease involves detecting the virus through Enzyme-linked immunosorbent assay (ELISA), real time polymerase chain reaction (RT-PCR) along with detecting IgM and IgG antibodies using ELISA. As for the treatment options for CCHF, they are finite as there are no available vaccines and the only antiviral drug used against the virus is ribavirin, which prevents replication of various DNA and RNA viruses in-vitro. Given all this information, it is evident that extensive research is necessary to better understand the disease holistically and design drugs that can stop more fatalities associated with CCHF.


Trichinellosis (parasite)


The next zoonotic disease to address is trichinellosis or trichinosis, which is caused by Trichinella spiralis and so it is a parasitic infection. It can spread by eating poorly prepared meat such as pork and mammals like horses and wild carnivores are typically the reservoirs of infection. Its epidemiology in humans seems to be limited because it has 10,000 cases and 0.2% death rate annually. Moreover, an important factor that can contribute to the spread of trichinellosis is culture because certain communities have dishes containing raw meat. For example, a review referenced more than 600 outbreaks, 38,797 infections and 336 deaths in humans between 1964 and 2011 in China. 


As for diagnosing trichinellosis, it is challenging because it has general signs. With this in mind, the common method to spot the disease is detecting IgG antigens that work against Trichinella spiralis. On the other hand, its major drawback is getting a false negative in early trichinellosis infection. Like CCHF, trichinellosis is not as prevalent compared to other zoonotic diseases but it can have devastating impacts on specific countries, so increasing the supply of antiparasitic drugs like albendazole and/or mebendazole would be beneficial to stop the spread of Trichinella spiralis. 


Brucellosis (bacteria)


The next zoonotic disease which is caused by a bacterial pathogen is brucellosis and is common worldwide, though certain places have higher prevalence of the disease compared to others. The pathogen can be transmitted through various ways such as direct contact with infected animal tissue on broken skin and consuming contaminated meat or dairy. Interestingly, it has been linked to childhood pulmonary infections as 18 out of 98 brucellosis patients have experienced such symptoms, but this is rare. 


The graph above indicates that when brucellosis occurs in animals, it has a high likelihood of being passed onto humans. For example, the years 2004-2007 could be when brucellosis cases were most frequent. This could have been alleviated through specific antibiotics used to treat brucellosis that include rifampin, doxycycline and streptomycin. Similar to trichinellosis, brucellosis diagnosis can be difficult because the symptoms can vary and are not exclusive to one disease, suggesting that different laboratory techniques are needed to find brucellosis in patients.   


Conclusion


It looks like there is a recurring pattern of the zoonotic diseases outlined in this article occurring in developing countries as opposed to developed countries. As such, there have to be more effective interventions to prevent their ramifications on populations living in these countries. For this to occur, there has to be sufficient information, awareness, and education of these rarer zoonotic diseases to begin with. Furthermore, the current treatments for CCHF, trichinellosis and brucellosis may be unsuccessful due to the threat of antimicrobial resistance, hence finding alternative treatments for the aforementioned zoonotic diseases is vital in the future. 



By Sam Jarada

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