Tick-Borne Diseases Could Increase with Global Warming

Some scientists believe that global warming could lead to increases in tick-borne diseases due to ticks spreading into previously unoccupied habitats.

There are about 15 tick-borne diseases caused by infection with Rickettsia bacteria. Related bacteria that cause Mediterranean spotted fever and Rocky Mountain spotted fever are transmitted by the brown dog tick, Rhipicephalus sanguineus, distributed widely around the world. The tick is well adapted to human environments and attaches to domestic dogs, but bites humans rarely.

One group of European scientists believe the brown dog tick may bring about the emergence of new human infections as average global temperatures increase, although they acknowledge that the risk of being bitten is small when another host is available to the ticks. But their research showed the ticks became aggressive to people before a domestic dog infested with them dies. This suggests that a lack of another host wasn’t the reason behind their behavior, and additional evidence points to unusually warm temperatures as the likely explanation.

Ticks need a humid environment to survive and are by nature aggressive, always looking for a host on which to attach. In warmer weather, the ticks could complete their life cycle faster, and higher temperatures could also mean that the air has more drying power. This kind of humidity-related stress can make ticks more eager to attach to a readily available source of blood.

Cholera Epidemic in Zimbabwe

The Zimbabwean government has declared a national emergency in the face of a cholera outbreak that has killed more than 560 people, to date. As of 1 Dec 2008, the Ministry of Health in Zimbabwe has reported a total of 11,735 cholera cases, affecting all provinces in the country. The overall case fatality rate is 4 percent but has reached up to 20-30 percent in remote areas.

Cholera is a severe diarrheal illness that spreads through contaminated water. Left untreated, it can cause death in a matter of hours.

The Limpopo River, which delineates the border between Zimbabwe and South Africa before flowing through Mozambique into the Indian Ocean, has tested positive for cholera, and appears to be the source of the epidemic.

The Vibrio cholerae bacteria occur naturally in coastal waters where they attach to tiny crustaceans called copepods. As many as 10,000 bacteria may adhere to a single crustacean. The bacteria travel with their hosts, spreading worldwide as the crustaceans follow their food source — certain types of algae and plankton that grow explosively when water temperatures rise. The rampant algae growth is further fueled by the urea found in sewage and in agricultural runoff.

Modern sewage and water treatment facilities have virtually eliminated cholera in industrialized nations; the last major cholera outbreak in the United States occurred in 1911. But the illness is still present in much of the world, particularly India and sub-Saharan Africa. The risk of epidemics is highest when poverty, war or natural disasters force people to live in crowded conditions without adequate sanitation.

The great irony is that unlike many infectious diseases, cholera is easily treated. Death results from severe dehydration, which can be prevented with a simple and inexpensive rehydration solution.

Although V. cholerae is the source of cholera infection, the deadly effects of the disease are the result of a potent toxin, CTX, that the bacteria produce in the small intestine. CTX binds to the intestinal walls, where it interferes with the normal flow of sodium and chloride. This causes the body to secrete enormous amounts of water, leading to diarrhea and a rapid loss of fluids and salts (electrolytes).

The UN children's agency, UNICEF, said in a statement: "The onset of the rainy season threatens to make the waterborne disease endemic, as the spread of cholera becomes increasingly unpredictable and the response is outpaced by the outbreaks. Harare (the capital of Zimbabwe), where the highest numbers of cholera cases have been reported, continues to experience serious water outages."

The cholera epidemic is now affecting 42 of Zimbabwe's 62 districts.

Dengue at Pandemic Levels

Dengue fever and dengue hemorrhagic fever (DHF) are viral diseases transmitted by Aedes mosquitoes, usually Aedes aegypti. The four dengue viruses (DEN-1 through DEN-4) are immunologically related, but do not provide cross-protective immunity against each other.

Dengue, a disease found in most tropical and subtropical areas of the world, has become the most common arboviral disease of humans. More than 2.5 billion persons now live in areas where dengue infections can be locally acquired. Epidemics caused by all four virus serotypes have become progressively more frequent and larger in the past 25 years. As of 2005, dengue fever is endemic in most tropical countries of the South Pacific, Asia, the Caribbean, the Americas, and Africa. Here are some of the latest reports:

Viet Nam: Heavy rains have again hit northern Viet Nam following the worst floods to hit the region in over 35 years. Authorities in the capital say they are trying to contain the spread of dengue fever after 180 cases of the mosquito-borne disease were reported by Hanoi hospitals in a 6 day period. The number of dengue cases is likely to rise as people store drinking water, thus providing more breeding sites for the dengue virus vector mosquito, Aedes aegypti.

Pakistan: Within 48 hours, 154 fresh cases of dengue fever were confirmed in the government hospitals in Punjab on 6 Nov 2008. The Punjab Health Department said that the number of dengue patients has soared to 437.

South Pacific: Samoa, Tonga, Kiribati, New Caledonia, and Palau have reported high levels of dengue fever. In Fiji, there are about 2000 people infected from a population of just over 900 000. It is probable that a new dengue virus serotype is circulating in these areas and that existing immunity from previous infections by other dengue virus serotypes is not protective.

Mexico: There have been 32 confirmed cases of classical dengue fever in Parque Hundido and surrounding neighborhoods of the Gomez Palacio municipality of Durango. The Parque Hundido neighborhood continues to be the area most affected by dengue, not only in the Gomez Palacio area, but in the whole of the Comarca Lagunera. Comarca Lagunera is the large metropolitan area located on the border between the states of Coahuila and Durango that includes 15 municipalities.

Authorities are emphasizing the need for standard precautions - eliminating all possible water catchments, such as buckets, tubs, flower vases, and bottles; cleaning up patios; putting mosquito larvicide in water-based heat pump systems; opening windows when fumigation machines pass by; and using insect repellants and
insecticides in the house.

Dengue fever is characterized by sudden onset after an incubation period of 3-14 days (most commonly 4-7 days) of high fevers, severe frontal headache, and joint and muscle pain. Many patients have nausea, vomiting, and a maculopapular rash, which appears 3-5 days after onset of fever and can spread from the torso to the arms, legs, and face. The disease is usually self-limited, although convalescence can be prolonged. Most patients report a nonspecific viral syndrome or a flu-like illness. Asymptomatic infections are also common. Although these patients do not experience symptoms at the time of the acute infection, the immunity that results increases the risk for DHF during a subsequent infection. Approximately 1% of patients with dengue infection progress to DHF. As the patient’s fever resolves, usually 3-5 days following the onset of fever, patients may develop leaky capillaries, which allow serum proteins and fluid to accumulate in the pleural and abdominal cavities. Thrombocytopenia and hemorrhagic manifestations, which can range from microscopic hematuria or increased menstrual flow to hemetemesis, are part of the syndrome. Neutropenia, elevated liver enzymes, and disseminated intravascular coagulation are also common. The case-fatality ratio for DHF averages about 5% worldwide, but can be kept below 1% with proper clinical management. Dengue shock syndrome is the progression of DHF to a hypotensive state. Despite the name, the progression of DHF to DSS is primarily due to capillary leakage rather the hemorrhaging.

Rare Jamestown Canyon Virus Strikes in Mississippi

The Mississippi State Department of Health reported a case of Jamestown Canyon virus (JCV) in Lamar County today. The clinical details of the case were not made available; however, symptoms of infection can vary from none to encephalitis.

JCV is endemic and widely distributed in the USA from the Rocky Mountains eastward, causing sporadic cases of febrile disease and encephalitis in humans. Cases of JCV infection occur occasionally in Mississippi; most recently in 2006.

JCV circulates among deer, horses, and other large wild and domestic mammals by way of mosquito bites. It can also be transmitted to humans by the same mechanism. The virus is relatively rare, but may be carried by several types of mosquito, including the tree hole mosquito, Ochlerotatus (Aedes) triseriatus.

JCV is one of 14 related viruses belonging to the California encephalitis virus species. This is one of a large number of species comprising the genus Bunyavirus of the family Bunyaviridae.

A New Deadly Virus in Africa

The deaths of three people due to a mysterious disease in Zambia and South Africa have demanded the attention of the South African government and the US Centers for Disease Control (CDC).

Preliminary tests indicated that the mystery disease was caused by a virus from the family that includes Lassa fever, the United Nations World Health Organization (WHO) said.

Investigations began after an office employee at a safari tour company in Zambia died on September 14 in a hospital in Johannesburg, South Africa, two days after undergoing a medical evacuation from Zambia.

A paramedic who cared for that patient was later admitted to hospital in Johannesburg and died on October 2, and a nurse who was also involved in the care of the first patient died on October 5.

The three experienced fever, headaches, diarrhea and myalgia that developed into rash and hepatic dysfunction followed by rapid deterioration and death.

A fourth case has now been confirmed to be a nurse who had close contact with one of the earlier cases. She has been admitted to a hospital in South Africa.

Arenaviruses cause chronic infections in some wild African mice. The infected mice excrete the virus in their urine, which can then contaminate human food or house dust. Viruses similar to the Lassa fever virus have been found in rodents in Africa; but other than those in West Africa, they have not been found to cause diseases in humans. It remains to be determined whether this is a previously unrecognized member of the arenaviruses.