Travel medicine: A closer look at the world
map Are you looking for information on diseases
with regional patterns? In this Chalk Talk episode, we’ll provide you with a general
overview and brief introduction on diseases to consider. This includes distribution patterns,
modes of transmission, and main symptoms. So, what are we waiting for? Let’s go explore
the map of the world. Schistosomiasis is a parasitic disease acquired
by contact with contaminated freshwater. It’s caused by schistosoma trematodes, also
known as blood flukes. The parasites usually live in freshwater, where they mature into
snails. The infectious larvae, also termed cercaria, can penetrate the skin when humans
come into contact with contaminated water. This can cause a pruritic maculopapular rash
at the point of entry, commonly known as swimmer’s itch. The parasites then migrate to the liver.
Apart from a local reaction, most infections are asymptomatic; however, in some individuals,
the eggs or adult worms are recognized by the immune system, resulting in Katayama fever,
an acute form of schistosomiasis. Symptoms include fever, cough, and angioedema. Depending
on the schistosoma type, adult worms migrate to the intestine or bladder, resulting in
two main forms of chronic schistosomiasis. These forms occur in response to egg deposition
and are the result of chronic inflammation. Intestinal schistosomiasis presents with abdominal
pain and bloody diarrhea, whereas clinical findings in urogenital schistosomiasis are
dysuria and hematuria. If the eggs enter the bloodstream, they’re transported to other
organs such as the liver, kidney, or central nervous system. Schistosomiasis is the leading
cause of portal hypertension worldwide. The regional distribution of the different
chronic forms depends on the distribution pattern of the parasite. Intestinal schistosomiasis
is prevalent in South America and Asia, whereas urogenital schistosomiasis is more common
in the Middle East and Northern Africa. Both forms are frequently observed in other regions
of Africa. The only preventative measure against infection
is to avoid contact with freshwater in endemic areas. Schistosomiasis can be effectively
treated with the anthelmintic praziquantel. The most historically feared disease by travellers
is malaria. It clinically presents with nonspecific findings
such as fever, nausea, and vomiting after an incubation period of 1 to 6 weeks. Despite
its prevalence in Africa, South America, and Southeast Asia, approximately 90% of more
than 200 million annual cases of malaria occur in Africa. Several types of malaria exist,
which are caused by different Plasmodium species. Among these, Plasmodium falciparum is the
most common, accounting for approximately three-quarters of cases worldwide. The female
Anopheles mosquito acts as a vector, transferring sporozoites through their bite. The sporozoites
enter the bloodstream of the human host and migrate to the liver. After maturation, they
re-enter the bloodstream and invade erythrocytes, which rupture and release merozoites that
induce febrile inflammatory response. As a preventative measure, travellers are
strongly advised to use exposure prophylaxis, such as mosquito repellents and mosquito nets.
In addition, chemoprophylaxis can be used. The drug of choice depends on the destination
and duration of stay, and considers the current status of drug resistance. However, antimalarial
drugs don’t prevent infection. Instead, they alleviate clinical manifestations by
attacking developmental forms of the parasite. Due to the strong adverse effects of chemoprophylaxis,
a detailed look at the local risk of malaria should be made. As a general rule of thumb,
there’s no risk of malaria infection in locations with temperatures below 15°C, which
are in various high altitude areas in the tropics.
Another mosquito-borne febrile disease is dengue fever. It’s caused by infection with
dengue virus and is primarily transmitted by the Aedes aegypti mosquito. Therefore,
the risk areas of dengue infection cover most of the distribution areas of Aedes aegypti.
Dengue is found in tropical and subtropical regions worldwide, especially in Southeast
Asia, but also in central and South America, Africa, Oceania, and Northeast Australia.
Although approximately 90% of infected individuals remain asymptomatic, a severe course with
hemorrhagic fever occurs in 1–2% of cases. Dengue hemorrhagic fever is characterized
by bleeding, shock, and organ dysfunction, and can be fatal. Progression to severe forms
occur especially in patients with either concurrent infection with different serotypes of dengue
virus or in patients immune to one or more serotypes as a result of previous infection.
A live-attenuated vaccine is currently available in some endemic countries; however, it isn’t
recommended for travellers. Dengue prevention is limited to avoiding mosquito
exposure in endemic areas. Aedes mosquitoes are also involved in the
transmission of another haemorrhagic fever, yellow fever. This disease is currently more
localized than dengue fever and malaria. Most yellow fever infections occur in sub-Saharan
Africa between 15 degrees north and 18 degrees south of the equator. Other regions of risk
for travellers are the tropical regions of northern South America. This region is also
referred to as the “yellow fever belt”. The disease is caused by yellow fever virus,
which can result in viral hemorrhagic fever. Clinical manifestations include liver dysfunction,
renal failure, disseminated intravascular coagulation, and shock.
The most effective preventative measure against yellow fever is vaccination, with a single-dose
vaccine available that provides lifelong protection. Some countries require travellers coming from
yellow fever endemic areas to provide proof of vaccination.
The protozoan parasite Trypanosoma brucei is restricted to sub-Saharan Africa, giving
rise to a disease that is best known as “sleeping sickness”, or African trypanosomiasis. The
parasites are transmitted by the tsetse fly. There are two different forms of the disease
that are caused by different pathogens: The West African form and East African form, which
are designated by their geographic distributions. Patients initially present with painful, red
swelling at the site of the bite. This is followed by a hemolymphatic phase, where the
patients develop intermittent fever, lymph node swelling, anemia, and immune reactions
in different organ systems such as the central nervous system and the cardiac system. The
neurological phase begins a few months to years after infection in the case of West
African trypanosomiasis or within a few weeks in case of East African trypanosomiasis. Clinical
findings include headache, daytime somnolence, which gives rise to its name sleeping sickness,
ataxia, delayed hyperesthesia, cachexia, and eventually coma.
The only preventative measure is to avoid exposure by using insect repellents, wearing
long sleeve clothing, and avoiding areas inhabited by the tsetse fly.
As the protozoan parasite Trypanosoma is not limited to Africa, it should come as no surprise
that an American form of trypanosomiasis exists. The disease is widely known as Chagas disease.
Chagas disease is endemic in Central and South America and is transmitted by the triatomine
bug, also known as kissing bug. Infections reported in Northern America and Europe are
either imported or infrequently acquired through blood transfusion, organ transplantation,
or vertical transmission from mother to fetus. Shortly after infection, patients develop
a characteristic, local skin lesion at the site of the bite, which is also known as a
chagoma. The acute phase of infection manifests with
nonspecific symptoms such as fever, malaise, and generalized lymphadenopathy. The asymptomatic
intermittent phase is followed by a chronic phase with the development of cardiomyopathy
characterized by arrhythmias, megaesophagus, and megacolon. In contrast to sleeping sickness,
the central nervous system is rarely affected in Chagas disease.
Prophylactic measures for travelers are preventing exposure to the vector by using insect repellents
and bed nets treated with insecticides. A disease that poses a risk for individuals
travelling to the Northern hemisphere is Lyme disease, also termed borreliosis. Lyme disease
is caused by bacteria of the Borrelia type, which are transmitted by ticks. The vector
is most prevalent in areas endemic for Lyme disease. Infected ticks can be found in the
Northeastern and upper Midwestern US and Europe, as well as in Russia.
If left untreated, Lyme disease can proceed in three stages, beginning with an early localized
rash, eventually causing a systemic infection involving joints, skin, and central nervous
system. As there is no vaccine available against Lyme
disease, preventative measures comprise of preventing exposure to ticks, as well as the
immediate removal of the tick after biting. Removal lowers the risk of infection, as transmission
usually occurs after an attachment time between 12 and 24 hours. In addition, close observation
of the bite site is advised, because the presence of a classical erythema migrans may indicate
infection. However, not all cases of Lyme disease are accompanied by erythema. Lyme
disease can be treated with antibiotics, with early treatment resulting in the highest success
rates. Therefore, any sign of infection should signal the start of further diagnostics and,
if indicated, treatment. Another viral infectious disease to be on
the lookout for in the Northern hemisphere is tick-borne encephalitis, which is caused
by tick-borne encephalitis virus, in short TBEV. Apart from it’s regional distribution,
transmission is more frequent during summer, with infection rates highest during this period.
Approximately 90% of infections remain asymptomatic; however, the remaining 10% initially show
flu-like symptoms and fever. After a fever-free interval, the central nervous system is affected,
typically manifesting as meningoencephalitis. Treatment of meningoencephalitis is supportive
and based on the severity of symptoms, but usually leads to full recovery.
As a preventive measure, vaccines against TBEV are available; however, they are only
recommended to individuals travelling to endemic regions where they’re more likely to be
exposed to ticks. Preventative measures to avoid tick bites are generally advised. Immediate
removal of the tick after biting doesn’t further reduce the risk of infection with
TBEV, as the virus is transferred directly after biting.
One well-known disease that occurs on a global scale is rabies. The disease is often fatal
and is caused by lyssaviruses, which include the rabies virus.
In encephalitic rabies, initial symptoms include agitation, confusion, and hypersalivation,
followed by coma and death. Rabies is usually transmitted through the
bite of an infected animal, most likely a dog or a bat. The regions high at risk for
rabies infection are Africa and South-East Asia; however, transmission through wild animals
can occur in almost all geographical locations, including central and South America, and Europe.
As there is no drug available against rabies virus infection, prophylaxis is highly recommended.
Pre-exposure rabies vaccination is ideal; however, treatment consisting of post-exposure
vaccination and rabies immunoglobulin after suspected exposure is particularly effective.
So, let’s summarize what we’ve just covered. Individuals preparing to travel should be
informed about potential risks in the countries that they’re travelling to. This includes
determining whether the regions are at risk for diseases that can be prevented by administering
a vaccine prior to departure. Also, it’s usually quite helpful to be cautious
about drinking water sources and food, especially if it’s not well cooked. For any outdoor
activities, it’s advisable to minimize exposure to insects, which are often vectors of pathogens.
We do admit that it’s difficult to remember all of this information. But don’t worry;
it’s all available in our library. So, let’s see how much you know about these
travel-relevant diseases in our quiz.
With their annoying hums, buzzing wings, and irritating bites, mosquitos can keep you awake all night. These tiny creatures have been sucking blood for 200,000,000 years. Besides what a nuisance mosquitos are, they are also responsible for spreading several viral diseases, like yellow fever, dengue, chikungunya,
and the Zika virus. If you’ve never heard of Zika until now,
you’re not alone. The Zika virus is a mosquito-borne disease spread by the Aedes Aegypti mosquito. In order to transmit Zika, a female mosquito carrying the virus must first find a human host, by following traces of
carbon dioxide, odor, and body temperature in the air. When a mosquito bites, it inserts its needle-like proboscis into the skin. The proboscis is made of two tubes – One tube injects saliva containing an enzyme that prevents the host’s blood from clotting; while the other tube pumps blood out. Once the mosquito bites, the virus is transmitted instantly to the host. If you live in an area prone to mosquitos, the risk of transmitting the virus increases. Once a person becomes infected with Zika, mild symptoms may begin to develop within a few days, Including: fever, rash, conjunctivitis and joint pain. Fortunately hospitalization is very rare, and the disease usually clears up within a week. Besides mosquitos, Zika can also be transmitted through: blood transfusions, sexual intercourse, and from mother to unborn child during pregnancy. While Zika is problematic for everyone, the most serious concern is its effect on a developing fetus. Since the Brazilian outbreak began in May 2015, Over 4,000 babies have been born with microcephaly, a serious condition in which a baby is born with an underdeveloped brain and a smaller-than-normal head. Scientists believe there may be a link between Zika and microcephaly, but more information is still needed. Fortunately, there are some simple steps you can take to protect yourself and your family: Eliminate mosquito breeding locations by
emptying containers where standing water has accumulated. Spray insecticide around ponds, Light citronella candles, and wear EPA certified insect repellant when outdoors. Stay in places with air conditioning, and make sure your windows and doors are screened in. and… wear long sleeves and long pants. If you’re pregnant, consider postponing travel to places where Zika is spreading. Check the CDC’s website for the most up-to-date travel recommendations. So remember, while there isn’t a vaccine or medication for Zika yet, you can reduce your risk by staying informed, and doing your best to avoid mosquitos.